Association of a common allelic polymorphism (C677T) in the methylene tetrahydrofolate reductase gene with a reduced risk of osteoporotic fractures. A case control study in Danish postmenopausal women

Genetic variants modify the associations of concentrations of methylmalonic acid, vitamin B-12, vitamin B-6, and folate with bone mineral density

BACKGROUND

Elevated plasma homocysteine has been found to be associated with an increased risk of osteoporosis, especially hip and vertebral fractures. The plasma concentration of homocysteine is dependent on the activities of several B vitamin-dependent enzymes, such as methylenetetrahydrofolate reductase (MTHFR), methionine synthase (MTR), methionine synthase reductase (MTRR), and cystathionine β-synthase (CBS).

OBJECTIVES

We investigated whether genetic variants in some of the genes involved in 1 carbon metabolism modify the association of B vitamin-related measures with bone mineral density (BMD) and strength.

METHODS

We measured several B vitamins and biomarkers in participants of the Framingham Offspring Study, and performed analyses of methylmalonic acid (MMA) continuously and <210 nmol/L; pyridoxal-5'-phosphate; vitamin B-12 continuously and ≥258 pmol/L; and folate. The outcomes of interest included areal and volumetric BMD, measured by DXA and quantitative computed tomography (QCT), respectively. We evaluated associations between the bone measures and interactions of single nucleotide polymorphism with a B vitamin or biomarker in Framingham participants (n = 4310 for DXA and n = 3127 for QCT). For analysis of DXA, we validated the association results in the B-PROOF cohort (n = 1072). Bonferroni-corrected locus-wide significant thresholds were defined to account for multiple testing.

RESULTS

The interactions between rs2274976 and vitamin B-12 and rs34671784 and MMA <210 nmol/L were associated with lumbar spine BMD, and the interaction between rs6586281 and vitamin B-12 ≥258 pmol/L was associated with femoral neck BMD. For QCT-derived traits, 62 interactions between genetic variants and B vitamins and biomarkers were identified.

CONCLUSIONS

Some genetic variants in the 1-carbon methylation pathway modify the association of B vitamin and biomarker concentrations with bone density and strength.  These interactions require further replication and functional validation for a mechanistic understanding of the role of the 1-carbon metabolism pathway on BMD and risks of fracture.

3'-UTR Polymorphisms of MTHFR and TS Associated with Osteoporotic Vertebral Compression Fracture Susceptibility in Postmenopausal Women

Postmenopausal osteoporosis is one of the most prominent diseases in postmenopausal women and it is increasing in prevalence with the aging population. Furthermore, osteoporosis and osteoporotic vertebral compression fractures (OVCFs) are related to mortality and decreased quality of life. Therefore, searching for biomarkers that are able to identify postmenopausal women who are at high risk of developing OVCFs is an effective strategy for improving the quality of life of patients and alleviating social and economic burdens. In this study, we investigated methylenetetrahydrofolate reductase (MTHFR) and thymidylate synthase (TS) gene polymorphisms in postmenopausal women with OVCF. We recruited 301 postmenopausal women and performed genotyping for the presence of MTHFR 2572C>A, 4869C>G and TS 1100C>T, 1170A>G. Genotyping was analyzed using the polymerization chain reaction restriction fragment length polymorphism assay. MTHFR 2572C>A and TS 1100C>T were associated with the prevalence of osteoporosis (MTHFR 2572CC versus CA+AA: odd ratio [OR] adjusted age, hypertention [HTN], and diabetes mellitus [DM] = 0.49, p = 0.012) and the occurrence of OVCFs (MTHFR 2572CC versus CA+AA: OR adjusted age, HTN, and DM = 0.38, p = 0.013; TS 1100CC versus CT+TT: OR adjusted age, HTN, and DM = 0.46, p = 0.02). Our novel finding is the identification of MTHFR and TS genetic variants that decrease susceptibility to OVCFs. Our findings suggest that polymorphisms in the MTHFR and TS genes are associated with susceptibility to osteoporosis and OVCFs in postmenopausal women.

Association of blood lead levels with methylenetetrahydrofolate reductase polymorphisms among Chinese pregnant women in Wuhan city

BACKGROUND

Pregnancy is an important stimulus of bone lead release. Elevated blood lead levels (BLLs) may cause adverse pregnancy outcomes for mothers and harmful lead effects on fetuses. However, the reports about maternal BLL changes during pregnancy are conflicting to some extent. This article is to explore the variations in BLLs among pregnant women. The relationships of BLLs with methylenetetrahydrofolate reductase (MTHFR) gene C677T, A1298C, and G1793A polymorphisms, which are associated with bone resorption, were also studied. A total of 973 women, including 234, 249, and 248 women in their first, second, and third trimesters, respectively, and 242 non-pregnant women, were recruited at the Wuhan Women and Children Medical Health Center.

METHODS

BLLs were determined using a graphite furnace atomic absorption spectrometer. Single-nucleotide polymorphisms of MTHFR were identified with the TaqMan probe method.

RESULTS

The geometric mean (geometric standard deviation) of BLLs was 16.2 (1.78) μg/L for all participants. All the studied MTHFR alleles were in Hardy-Weinberg equilibrium. Multiple-linear regression analysis revealed the following results. Among the pregnant women, those that carried MTHFR 677CC (i.e. wild-genotype homozygote) and 1298CC (i.e. mutant-genotype homozygote) exhibited higher BLLs than those that carried 677CT/TT (standardized β = 0.074, P = 0.042) and 1298AC/AA (standardized β = 0.077, P = 0.035) when other covariates (e.g., age, no. of children, education and income, etc.) were adjusted. The BLLs of pregnant women consistently decreased during the pregnancy and these levels positively correlated with BMI (standard β = 0.086-0.096, P<0.05).

CONCLUSIONS

The 1298CC mutant-type homozygote in the MTHFR gene is a risk factor for high BLLs among low-level environmental lead-exposed Chinese pregnant women, whose BLLs consistently decreased during gestation.

Association of Methylene Tetrahydrofolate Reductase Polymorphism with BMD and Homocysteine in Premenopausal North Indian Women

BACKGROUND AND AIM

Osteoporosis (OP) is a common nutrigenomic disease associated with various genetic components. Observational studies have indicated that mildly elevated homocysteine was a strong risk factor for osteoporotic fractures. Yet there is no clear biologic mechanism for an effect of homocysteine on bone.The aim of this study was to investigate the association of MTHFR C677T and A1298C polymorphisms, and to verify the association of these polymorphisms with bone mineral density and homocysteine in premenopausal women of northern India.

MATERIAL AND METHODS

We included 402 north Indian patients with altered BMD, both Osteopenic (OPN) and Osteoporosis, and normal controls. Genotype identification for MTHFR C677T and A1298C polymorphisms were analyzed by PCR-RFLP method, correlated with Bone Mineral Density (BMD), Homocysteine (Hcy), Folate and Vitamin B12.

RESULTS

The study groups did not differ in terms of age, weight and body mass indices. Prevalence of Genotype frequencies (GFs) for MTHFRC677T OP were (n: 402): CC 361 (89.8%), CT 25 (6.22%), TT 16 (3.98%) and that for MTHFR A1298C were (n: 402) AA 353(87.81%), AC 29(7.21%), CC 20(4.98%). Folate was significantly lower in the OP group than those in both the other groups, while there was no significant difference in Hcy in the OP group relative to OPN, as compared to controls.

CONCLUSION

The GFs for MTHFR C677T and A1298C polymorphisms were not different between both groups. In conclusion, polymorphism of the MTHFR 677T is associated with small differences in BMD with folate levels. Further, more investigations should be done in larger studies for other epigenetic pathways, that may increase the risk of Osteoporosis.

Polymorphism of SLC25A32, the folate transporter gene, is associated with plasma folate levels and bone fractures in Japanese postmenopausal women

AIM

Elevation of homocysteine is associated with an increased risk for bone fractures. We previously reported that the methylenetetrahydrofolate reductase (MTHFR) gene polymorphism is associated with homocysteine levels and fracture. The association between the fracture and folate levels or their related gene polymorphisms is not completely clear. We speculated that the SLC25A32 gene, the mitochondrial inner membrane folate transporter, also could be implicated in the regulation of folate metabolism and fracture.

METHODS

A total of 851 Japanese postmenopausal women participated in the association study between the single nucleotide polymorphism genotype and plasma homocysteine or folate. We also tested the association between the candidate single nucleotide polymorphism and 663 postmenopausal women.

RESULTS

The AA genotype of rs2241777 single nucleotide polymorphism at the 3'UTR region in the SLC25A32 gene was associated with lower plasma folate concentration compared with the other genotypes in 851 postmenopausal women. A total of 674 postmenopausal ambulatory Japanese women were followed up for 5.5 ± 0.1 years (mean ± SE). The AA genotype groups also showed an apparently higher rate and earlier onset of incident fractures than the other genotypes. A total of 407 participants had >70% young-adult mean bone mineral density at the start of the observation.

CONCLUSIONS

These results show that the SLC25A32 gene polymorphism could be a risk factor for lower folate concentration and future fracture.

Association of the MTHFR C677T polymorphism and bone mineral density in postmenopausal women: a meta-analysis

Osteoporosis is a condition characterized by low bone mineral density (BMD) and micro-architectural changes in the bone tissue. The risk of osteoporosis is partly determined by genetic factors. The role of C677T polymorphism of methylenetetrahydrofolate reductase (MTHFR) gene has been investigated in postmenopausal osteoporosis. However, the relationship between MTHFR polymorphism and BMD is still controversial. We carried out a meta-analysis of 5,833 subjects to evaluate the association of MTHFR and BMD in postmenopausal women. Databases of MEDLINE, Web of Science, Scopus and CNKI were retrieved for all publications relating to MTHFR polymorphism and BMD in postmenopausal women. Five eligible studies were selected for meta-analysis. All these articles studied the association of MTHFR polymorphism and BMD of the femoral neck and lumbar spine in postmenopausal women. Our analysis suggested that postmenopausal women with the TT genotype had lower femoral neck BMD than the women with the CC/CT genotype, and the weighted mean difference (WMD) was -0.01 g/cm(2) [95% confidence interval (CI): (-0.01, -0.01), P < 0.01]. However, BMD of the lumbar spine of postmenopausal women with the TT genotype was not significantly different from that of women with the CC/CT genotype. In the random effects model, the WMD between the TT and TC/CC genotype was -0.01 g/cm(2) [95% CI: (-0.04, 0.01), P = 0.32]. The C677T polymorphism of the MTHFR gene is associated with BMD of the femoral neck in postmenopausal women. Women with the TT genotype of the MTHFR gene have lower BMD, suggesting that the TT genotype may be a risk factor for postmenopausal osteoporosis.

Association of MTHFR C667T polymorphism with bone mineral density and fracture risk: an updated meta-analysis

This meta-analysis investigated the association of C677T polymorphism in MTHFR gene with bone mineral density (BMD) and fracture risk. The results suggested that C677T polymorphism was marginally associated with fracture risk. In addition, this polymorphism was modestly associated with BMD of lumbar spine, femoral neck, total hip, and total body, respectively.

INTRODUCTION

The methylenetetrahydrofolate reductase (MTHFR) gene has been implicated in the regulation of BMD and, thus, may serve as a potential risk factor for the development of fracture. However, results have been inconsistent. In this study, a meta-analysis was performed to clarify the association of C677T polymorphism in MTHFR gene with BMD and fracture risk.

METHODS

Published literature from PubMed and EMBASE were searched for eligible publications. Pooled odds ratio (OR) or weighted mean difference (WMD) and 95% confidence interval (CI) were calculated using a fixed- or random-effects model.

RESULTS

Twenty studies (3,525 cases and 17,909 controls) were included in this meta-analysis. The TT genotype of C677T polymorphism was marginally associated with an increased risk of fracture under recessive model (TT vs. TC + CC: OR = 1.23, 95% CI 1.04-1.47). Using this model, similar results were found among East Asians (OR = 1.40, 95% CI 1.07-1.83), female subpopulation (1.27, 95% CI 1.04-1.55), cohort studies (OR = 1.24, 95% CI 1.08-1.44), and subjects younger than aged 60 years (OR = 1.51, 95% CI 1.10-2.07). In addition, under homogeneous co-dominant model, there was a modest association of C677T polymorphism with BMD of lumbar spine (WMD = -0.017 g/cm(2); 95%CI, -0.030-(-0.005) g/cm(2)), femoral neck (WMD = -0.010 g/cm(2); 95% CI -0.017-(-0.003) g/cm(2)), total hip (WMD = -0.013 g/cm(2), 95% CI -0.022-(-0.004) g/cm(2)), and total body (WMD = -0.020 g/cm(2); 95% CI -0.027-(-0.013) g/cm(2)), respectively.

CONCLUSIONS

This meta-analysis suggested that C677T polymorphism was marginally associated with fracture risk. In addition, this polymorphism was modestly associated with BMD of lumbar spine, femoral neck, total hip, and total body, respectively.

The association between plasma homocysteine levels, methylation capacity and incident osteoporotic fractures

BACKGROUND

An elevated level of plasma homocysteine (Hcy) is a known risk factor for osteoporotic fractures. In addition, Hcy is related to DNA-methylation metabolism. To determine whether the association between Hcy and fractures is explained by an altered methylation capacity, we investigated the associations between levels of s-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) and fracture risk.

METHODS

We studied 503 females aged 55 years and over from the Rotterdam Study (RS) in whom plasma Hcy, SAM and SAH levels were measured. Bone mineral density (BMD) at the hip was assessed using DXA. Incident fractures were recorded over a mean period of 7.0 years. Cox proportional hazards analysis and linear regression were used to assess relationships between plasma metabolite levels, incident osteoporotic fractures and BMD.

RESULTS

Over a total of 3502 person-years of follow-up, 103 subjects sustained at least one osteoporotic fracture. Whereas incidence of osteoporotic fractures was associated with quartiles of Hcy (p=0.047), it was not associated with quartiles of SAM, SAH or SAM/SAH-ratio (all p for trend>0.6). Stepwise linear regression showed that SAM/SAH-ratio, but not Hcy, was independently associated with hip BMD (β=0.073, p=0.025).

CONCLUSION

Since SAM, SAH and SAM/SAH-ratio were not associated with osteoporotic fractures, alterations in methylation capacity most likely do not appear to be an important factor in the association between Hcy and fractures.

The IL6 gene polymorphism -634C>G and IL17F gene polymorphism 7488T>C influence bone mineral density in young and elderly Japanese women

Osteoporosis is an important public health problem because of the significant morbidity and mortality associated with its complications, particularly fractures. An important clinical risk factor in the pathogenesis of osteoporosis is the presence of genetic polymorphisms in susceptibility genes. However, few studies have investigated the relevance of these polymorphisms in premenopausal women. Recent studies have demonstrated interactions between bone and immune cells, and that cytokines produced by immune cells regulate bone turnover. In this study, we examined the associations between bone mineral density (BMD) and polymorphisms in genes encoding interleukin (IL)-6 (-634C>G; rs1800796), tumor necrosis factor (TNF)-α (-308G>A; rs1800629), IL-17F (7488T>C; rs763780), transforming growth factor (TGF)-β (869T>C; rs1800470), osteoprotegerin (OPG; 163A>G; rs3102735) and methylenetetrahydrofolate reductase (MTHFR; 677C>T; rs1801133) in young and elderly Japanese women. Whole-body, lumbar spine (L(1) or L(2)-L(4)), and femoral neck BMD were measured in 100 young subjects (18-23 years), and 100 elderly subjects (60-83 years). Whole-body, lumbar spine, and femoral neck BMD were 1.13±0.06, 1.14±0.12, and 1.00±0.11 g/cm(2), respectively, in young subjects, and 0.92±0.09, 0.86±0.15, and 0.63±0.10 g/cm(2), respectively, in elderly subjects. The frequencies of the IL-6 CC, CG, and GG genotypes were 48%, 49%, and 3%, respectively. The frequencies of the IL17F TT, TC, and CC genotypes were 79%, 15%, and 6%, respectively, in young subjects. Polymorphisms of the IL-6 and IL17F genes were significantly associated with BMD. To our knowledge, this is the first report to examine these associations in a cohort of 200 Japanese women.

Serum homocysteine and asymmetric dimethylarginine levels in patients with premature ovarian failure: a prospective controlled study

OBJECTIVE

To investigate serum homocysteine and asymmetric dimethylarginine (ADMA) levels in patients with premature ovarian failure (POF).

STUDY DESIGN

A total of 69 women, 32 with POF and 37 apparently healthy women were included in the study. Fasting blood samples were drawn to measure serum homocysteine and ADMA levels using ELISA method.

RESULTS

The study and control group had a mean age of 37.3 + 2.6, 37.5 + 2.5 years; a mean homocysteine level of 13.54 + 5.19, 12.71 + 3.99 mmol/l and a mean ADMA level of 1.32 + 0.27, 1.26 + 0.36 mmol/l, respectively. There were no statistically significant differences between the two groups in terms of homocysteine and ADMA levels (with p values of 0.465 and 0.423, respectively). A negative significant correlation was found between estradiol and ADMA (p <0.05).

CONCLUSION

Homocysteine and ADMA levels did not change in comparison with the control group, which suggests that estrogen deficiency in patients with POF does not have any effect on homocysteine and asymmetric dimethylarginine levels.

Analysis of three functional polymorphisms in relation to osteoporosis phenotypes: replication in a Spanish cohort

Osteoporosis is a complex disease involving many putative genetic factors. Association analysis of functional SNPs in candidate genes is an important tool for their identification. However, this approach is affected by limited power, population stratification, and other drawbacks that lead to discordant results. Replication in independent cohorts is essential. We performed association analyses of three functional polymorphisms previously associated with bone phenotypes--namely, Ala222Val in MTHFR, Ile1062Val in LRP6, and -13910C>T in LCT--in a cohort of 944 postmenopausal Spanish women, all of them with lumbar spine (LS) bone mineral density (BMD) data and most with femoral neck (FN) BMD and fracture data. We found significant differences between genotypes only for the MTHFR polymorphism and vertebral factures, with an OR of 2.27 (95% CI 1.17-4.38) for the TT vs. CC/CT genotypes, P = 0.018. We present genotype and allele frequency data for LCT -13910C>T for a Spanish population, where the T allele (conferring lactase persistence) has a frequency of 38.6%. Genotype frequencies were consistent with observed clines in Europe and with the prevalence of lactase nonpersistence. The LCT -13910C>T polymorphism was significantly associated with height and weight, such that T allele carriers were 0.88 cm taller (95% CI 0.08-1.59 cm, P = 0.032, adjusted by age) than CC individuals and TT homozygotes were 1.91 kg heavier than CC/CT individuals (95% CI 0.11-3.71 kg, P = 0.038, adjusted by age). In conclusion, no significant association was observed between the studied polymorphisms and LS BMD or FN BMD in postmenopausal Spanish women, and only MTHFR Ala222Val was associated with vertebral fractures.

Bone morphogenetic protein-2 activity is regulated by secreted phosphoprotein-24 kd, an extracellular pseudoreceptor, the gene for which maps to a region of the human genome important for bone quality

The material properties of bone are the sum of the complex and interrelated anabolic and catabolic processes that modulate formation and turnover. The 2q33-37 region of the human genome contains quantitative trait loci important in determining the broadband ultrasound attenuation (an index of trabecular microarchitecture, bone elasticity, and susceptibility to fracture) of the calcaneus, but no genes of significance to bone metabolism have been identified in this domain. Secreted phosphoprotein-24 kd (SPP24 or SPP2) is a novel and relatively poorly characterized growth hormone-regulated gene that maps to 2q37. The purpose of this review is to summarize the status of research related to spp24 and how it regulates bone morphogenetic protein (BMP) bioactivity in bone. SPP24 codes for an extracellular matrix protein that contains a high-affinity BMP-2-binding transforming growth factor-beta receptor II homology 1 loop similar to those identified in fetuin and the receptor itself. SPP24 is transcribed primarily in the liver and bone. High levels of spp24 (a hydroxyapatite-binding protein) are found in bone, and small amounts are found in fetuin-mineral complexes. Full-length secretory spp24 inhibits ectopic bone formation, and overexpression of spp24 reduces murine bone mass and density. Spp24 is extremely labile to proteolysis, a process that regulates its bioactivity in vivo. For example, an 18.5-kd degradation product of spp24, designated spp18.5, is pro-osteogenic. A synthetic cyclized Cys(1)-to-Cys(19) disulfide-bonded peptide (BMP binding peptide) corresponding to the transforming growth factor-beta receptor II homology 1 domain of spp24 and spp18.5 binds BMP-2 and increases the rate and magnitude of BMP-2-mediated ectopic bone formation. Thus, the mechanism of action of spp18.5 and spp24 may be to regulate the local bioavailability of BMP cytokines. SPP24 is regulated by growth hormone and 3 major families of transcription factors (nuclear factor of activated T cells, CCAAT/enhancer-binding protein, Cut/Cux/CCAAT displacement protein) that regulate mesenchymal cell proliferation, embryonic patterning, and terminal differentiation. The gene contains at least 2 single nucleotide polymorphisms. Given its mechanism of action and sequence variability, SPP24 may be an interesting candidate for future studies of the genetic regulation of bone mass, particularly during periods of BMP-mediated endochondral bone growth, development, and fracture healing.

No association between hip geometry and four common polymorphisms associated with fracture: the Danish osteoporosis prevention study

Both osteoporosis and hip geometry are independently associated with fracture risk. There is a significant genetic contribution to the risk of osteoporosis, and evidence provided by twin studies has suggested that hip geometry may also in part be genetically programmed. Polymorphisms in a number of genes, including those coding for methylene-tetrahydrofolate reductase (MTHFR c.677C > T), the purinergic P2X(7) receptor (Glu496Ala and Ile568Asn), and the low-density lipoprotein receptor-related protein 5 (LRP5 exon 9 [c.266A > G]), have been associated with an increased fracture incidence and/or reduced bone mineral density (BMD). The aim of the present study was to test whether these polymorphisms influence hip structural geometry in perimenopausal women. The four polymorphisms were genotyped in 800 healthy recently perimenopausal women never using hormone replacement therapy. BMD of the femoral neck was measured using a Hologic QDR-2000 densitometer and femoral neck axis length, neck width, neck shaft angle, and femoral head diameter were measured from the screen images. Genotype frequencies were compatible with Hardy-Weinberg equilibrium. No significant differences between homozygotes for the minor allele and carriers of the common allele regarding parameters of hip geometry were demonstrated. According to the anthropometric characteristics of the subjects, only body height in the MTHFR TT genotype group was significantly different from the combined CT/CC genotype group (P < 0.05). The geometric dimensions of the proximal femur in perimenopausal women are not associated with the MTHFR c.677C > T, P2X(7) (Glu496Ala), P2X(7) (Ile568Asn), and LRP5 exon 9 (c.266A > G) polymorphisms.

Associations between methotrexate treatment and methylenetetrahydrofolate reductase gene polymorphisms with incident fractures in Japanese female rheumatoid arthritis patients

Several case reports have described associations between pathological nonvertebral fractures and low-dose methotrexate (MTX) in rheumatoid arthritis (RA) patients. Furthermore, a significant association between the C677T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene and incident fractures has been reported in postmenopausal women. We attempted to determine whether MTX use and MTHFR polymorphisms are associated with incident fracture risk in Japanese female RA patients. DNA samples, laboratory data, and clinical data were obtained from 731 female RA patients more than 50 years old as part of the Institute of Rheumatology Rheumatoid Arthritis (IORRA) observational cohort study. Genotyping of the MTHFR polymorphisms C677T and A1298C was performed using TaqMan SNP Genotyping Assays. MTX use, MTHFR polymorphisms, and other potential risk factors predictive of fracture were analyzed by Cox proportional hazards regression models, including time-dependent covariates. During 78 months from October 2000 to March 2007, 25 and 90 patients developed vertebral and nonvertebral fractures, respectively. Patients with nonvertebral fractures were more likely to take MTX (P = 0.011; odds ratio, 1.77; 95% confidence interval, 1.13-2.76) compared to patients without fractures. Although the C677T and A1298C polymorphisms were not significantly associated with incident fracture risk, MTX use, age, disease duration, and Japanese health assessment questionnaire score were significantly (P < 0.05) and independently associated with nonvertebral fracture incidence. Our results suggest that MTX use is associated with a nonvertebral fracture risk, whereas MTHFR polymorphism status does not appear to be a clinically useful marker for predicting fracture risk in Japanese female RA patients.

Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism is associated with spinal BMD in 9-year-old children

The C677T MTHFR polymorphism has been associated with lumbar spine and hip BMD. In older adults, the genetic effect has been reported in women only. However, in younger adults, this influence may only be present in men. This study is the first to investigate associations between the C677T MTHFR polymorphism and bone phenotypes in children. Regression analyses were used to study the relationship between MTHFR genotype and bone phenotypes derived from total body DXA scans in children 9.9 yr of age from the Avon Longitudinal Study of Parents and Children (ALSPAC). A total of 5816 children had both genetic and DXA data for the total body less head region (TBLH) and 3196 for the spine. A strong association was observed between the C677T MTHFR genotype and spine BMD (p < 0.001; 0.10 SD decrease per T allele). There was some evidence that this genetic effect was stronger in boys compared with girls (p = 0.04 for sex interaction). In contrast, there was no association between the C677T MTHFR genotype and TBLH BMD. The association between MTHFR genotype and spine BMD was attenuated particularly in girls by high maternal dietary intakes of vitamin B(6) and folate during pregnancy but not by child dietary intakes at 7 yr. To the extent that these findings reflect known influences of C677T MTHFR genotype on plasma homocysteine levels, our results suggest that the latter is an important regulator of spinal BMD in childhood.

Genetic variation in candidate osteoporosis genes, bone mineral density, and fracture risk: the study of osteoporotic fractures

Candidate osteoporosis gene variants were examined for associations with fracture risk and bone mineral density (BMD). A total of 9,704 white women were recruited at four U.S. clinical centers and enrolled into the Study of Osteoporotic Fractures, a longitudinal cohort study. Genotyping of 31 polymorphisms from 18 candidate osteoporosis genes was performed in 6,752 women. Incident radiographic fractures were identified at the third and eighth examinations compared with the baseline examination. BMD was measured at the total hip by dual-energy X-ray absorptiometry. Analyses were adjusted for age, clinic site, and self-reported ethnicity. During a mean follow-up of 14.5 years, a total of 849 hip, 658 vertebral, and 2,496 nonhip/nonvertebral fractures occurred in 6,752 women. Women carrying the ALOX15_G48924T T/T genotype had a higher rate of hip fracture (hazard ratio [HR] = 1.33;95% confidence interval [95% CI] = 1.00-1.77) compared with the G/G genotype. Compared with those carrying the PRL_T228C T/T genotype, women with either the C/C (HR = 0.80; 95% CI = 0.67-0.95) or C/T (HR = 0.81; 95% CI = 0.68-0.97) genotype had a lower rate of nonvertebral/nonhip fractures. Women carrying the BMP2_A125611G G/G genotype had a higher rate of vertebral fracture (odds ratio [OR] = 1.51; 95% CI = 1.03-2.23) compared with the A/A genotype. Women with the ESR1_C1335G G/G genotype had a higher rate of vertebral fracture (OR = 1.64; 95% CI = 1.07-2.50) compared with the C/C genotype. Compared with those with the MMP2_C595T C/C genotype, women with the C/T (OR = 0.79; 95% CI = 0.65-0.96) or T/T (OR = 0.44; 95% CI = 0.27-0.72) genotype had a lower rate of vertebral fracture. In conclusion, polymorphisms in several candidate genes were associated with hip, vertebral, and nonhip/nonvertebral fractures but not with total hip BMD in this large population based cohort study.

Genetics of osteoporosis

Osteoporosis is a frequent skeletal disorder, particularly among postmenopausal women. It affects approximately 30% of women and 12% of men above 50 years of age. It is characterized by reduced bone mass and alterations in bone microarchitecture that result in impaired bone strength and a propensity to fracture. Decreased bone mass is the consequence of an imbalance in the bone remodeling process, resulting from complex interactions between acquired and genetic factors. The former include physical activity, nutrition and other lifestyle habits, as well as the skeletal effects of some diseases and drug therapies. Genetic factors have been extensively studied during the past 15 years. We will review some important studies that exemplify the advances and the difficulties in this research field.

Relation of folates, vitamin B12 and homocysteine to vertebral bone mineral density change in postmenopausal women. A five-year longitudinal evaluation

Elevation of homocysteine is associated with an increased risk for bone fractures. Whether the risk is due to homocysteine or to the reduced levels of cofactors necessary for its metabolisation, such as folates or vitamin B12, is not completely clear. In this study we wanted to determine whether in postmenopausal women, levels of folates, homocysteine or vitamin B12 are predictive of the rate of vertebral bone mineral density (BMD) change. The study was conducted at the centre for the menopause of our university hospital. Between September 2001 and March 2002, 161 healthy postmenopausal women volunteered for a cross-sectional evaluation of BMD and levels of serum folates, homocysteine and vitamin B12. Women were recalled for a second evaluation of vertebral BMD after about 5 years. Women having used anti-resorptive therapies for more than 1 year were excluded. The analysis was possible in 117 postmenopausal women. The annual rate of vertebral BMD change was independently related to levels of folates (coefficient of regression (CR): 2.040; 95%CI: 0.483, 3.596; p=0.011), and initial BMD values (CR: -0.060; 95%CI: -0.117, -0.003; p=0.040). No significant relation was found between the change of vertebral BMD and homocysteine or vitamin B12. BMD values at the first (r=0.225; p=0.016) and the second (r=0.206; p=0.027) evaluation were related to levels of folates, but not of homocysteine or of vitamin B12. These data suggest an important role for folates deficiency in the vertebral BMD decline of postmenopausal women.

The synergistic effect of bone mineral density and methylenetetrahydrofolate reductase (MTHFR) polymorphism (C677T) on fractures

A functional polymorphism in methylenetetrahydrofolate reductase (MTHFR) has been identified at codon 677 (C677T). The T-allele variant (valine type) has lower enzyme activity than the wild type (C-allele or alanine type), resulting in a slightly elevated homocysteine level, which has been recently recognized as a risk factor for fracture. However, whether subjects bearing the T allele have higher susceptibility to fractures is still controversial. We have investigated the effects of MTHFR polymorphism on fracture susceptibility in Japanese postmenopausal women. A total of 502 postmenopausal ambulatory Japanese women were followed up for 5.1 +/- 3.4 (mean +/- SD) years, and a total of 155 patients with incident fractures (121 patients with vertebral fractures and 34 cases with fractures at other sites) were recorded. When compared with the patients without any fractures, the patients with incident fractures were older, had more prevalent fractures, had higher urinary levels of bone turnover markers as well as plasma homocysteine level, but were shorter in body height and had lower bone mineral density. The prevalence of the TT genotype of MTHFR was significantly higher in the patients with incident fractures compared to the other genotypes. The subjects with the TT genotype had a higher incidence rate of fracture and higher plasma level of homocysteine than the subjects bearing the non-TT genotype. This relationship was observed in both osteoporotic and nonosteoporotic groups. The hazard ratio for TT genotype without osteoporosis, non-TT genotype with osteoporosis, and TT genotype with osteoporosis was 1.49 (0.91-2.45), 3.64 (2.50-5.29), and 7.21 (4.34-11.97), respectively, compared to the non-TT genotype without osteoporosis. A higher hazard ratio for the TT genotype with osteoporosis was still apparent after adjustment for age, body size, and number of prevalent vertebral fractures. These results indicate that the TT genotype of MTHFR may be a risk factor for future fracture in addition to the traditional risk factors.

Low dietary riboflavin but not folate predicts increased fracture risk in postmenopausal women homozygous for the MTHFR 677 T allele

The MTHFR C677T polymorphism is associated with mildly elevated homocysteine levels when folate and/or riboflavin status is low. Furthermore, a mildly elevated homocysteine level is a risk factor for osteoporotic fractures. We studied whether dietary intake of riboflavin and folate modifies the effects of the MTHFR C677T variant on fracture risk in 5,035 men and women from the Rotterdam Study. We found that the MTHFR C677T variant interacts with dietary riboflavin intake to influence fracture risk in women.

INTRODUCTION

The MTHFR C677T polymorphism is associated with mildly elevated homocysteine (Hcy) levels in the presence of low folate and/or riboflavin status. A mildly elevated Hcy level was recently identified as a modifiable risk factor for osteoporotic fracture. We studied whether dietary intake of riboflavin and folate modifies the effects of the MTHFR C677T polymorphism on BMD and fracture risk.

MATERIALS AND METHODS

We studied 5,035 individuals from the Rotterdam Study, >or=55 yr of age, who had data available on MTHFR, nutrient intake, and fracture risk. We performed analysis on Hcy levels in a total of 666 individuals, whereas BMD data were present for 4,646 individuals (2,692 women).

RESULTS

In the total population, neither the MTHFR C677T polymorphism nor low riboflavin intake was associated with fracture risk and BMD. However, in the lowest quartile of riboflavin intake, female 677-T homozygotes had a 1.8 (95% CI: 1.1-2.9, p = 0.01) times higher risk for incident osteoporotic fractures and a 2.6 (95% CI: 1.3-5.1, p = 0.01) times higher risk for fragility fractures compared with the 677-CC genotype (interaction, p = 0.0002). This effect was not seen for baseline BMD in both men and women. No significant influence was found for dietary folate intake on the association between the MTHFR C677T genotype and fracture risk or BMD. In the lowest quartile of dietary riboflavin intake, T-homozygous individuals (men and women combined) had higher (22.5%) Hcy levels compared with C-homozygotes (mean difference = 3.44 microM, p = 0. 01; trend, p = 0.02).

CONCLUSIONS

In this cohort of elderly whites, the MTHFR C677T variant interacts with dietary riboflavin intake to influence fracture risk in women.

Searching for genes underlying susceptibility to osteoporotic fracture: current progress and future prospect

INTRODUCTION

Osteoporotic fracture (OF) is a public health problem. It is a common practice in the genetics of osteoporosis that bone mineral density (BMD) was studied as a major surrogate phenotype in gene search for risk of OF (ROF) because of their high phenotypic correlation. However, some studies indicate that the genetic correlation between BMD and ROF is very low. This implies that most genes found important for BMD may not be relevant to ROF. Ideally, employing OF per se as a direct study phenotype can directly find the relevant genes underlying ROF.

EVIDENCE

Here, we summarized some evidence supporting ROF under moderate genetic control, and the current progress of molecular genetic studies employing OF as the direct study phenotype, then give our consideration on the future prospects in the genetics of ROF.

Genetics of osteoporosis

Osteoporosis is a common disease with a strong genetic component characterised by reduced bone mass and an increased risk of fragility fractures. Twin and family studies have shown that genetic factors contribute to osteoporosis by influencing bone mineral density (BMD), and other phenotypes that are associated with fracture risk, although the heritability of fracture itself is modest. Linkage studies have identified several quantitative trait loci that regulate BMD but most causal genes remain to be identified. In contrast, linkage studies in monogenic bone diseases have been successful in gene identification, and polymorphisms in many of these genes have been found to contribute to the regulation of bone mass in the normal population. Population-based studies have identified polymorphisms in several candidate genes that have been associated with bone mass or osteoporotic fracture, although individually these polymorphisms only account for a small amount of the genetic contribution to BMD regulation. Environmental factors such as diet and physical activity are also important determinants of BMD, and in some cases specific nutrients have been found to interact with genetic polymorphisms to regulate BMD. From a clinical standpoint, advances in knowledge about the genetic basis of osteoporosis are likely to be important in increasing the understanding of the pathophysiology of the disease; providing new genetic markers with which to assess fracture risk and in identifying genes and pathways that form molecular targets for the design of the next generation of drug treatments.

Plasma homocysteine, folate, and vitamin B 12 and the risk of hip fracture: the hordaland homocysteine study

Homocysteine and related factors were evaluated as risk factors for subsequent hip fractures among 4766 elderly men and women. High levels of homocysteine and low levels of folate predicted fracture, whereas vitamin B12 and genotypes were not related to fracture risk. High homocysteine may be a modifiable risk factor for hip fracture.

INTRODUCTION

Elevated plasma total homocysteine (tHcy) and deficiencies of folate and vitamin B12 are associated with risk of osteoporosis and fracture. We examined whether plasma levels of tHcy, folate, and vitamin B12 and the methylenetetrahydrofolate reductase (MTHFR) 677C-->T and 1298C-->T polymorphisms predicted hip fracture.

MATERIALS AND METHODS

This was a population-based prospective study of 2639 women and 2127 men who were 65-67 yr at enrollment in 1992-1993. Information on hip fracture was obtained from computerized records of discharge diagnoses from all hospitalizations in the region in the period between enrollment and November 30, 2005. Cox proportional hazard regression was used to estimate fracture risk according to levels of plasma tHcy, folate, and vitamin B12 and for different genotypes.

RESULTS

Over a median follow-up period of 12.6 yr, hip fracture was recorded in 184 (7.0%) women and 90 (4.2%) men. The adjusted hazard ratio (95% CI) for fracture in subjects with high (>or=15 microM) compared with low levels (<9.0 microM) of tHcy was 2.42 (1.43-4.09) among women and 1.37 (0.63-2.98) among men. Dose-response analyses indicated a positive association between plasma tHcy and risk of fracture in both sexes and a negative association between plasma folate and risk of fracture among women only. Plasma vitamin B12 level or MTHFR genotype was not significantly related to risk of fracture after adjustments for confounding factors. The association between tHcy and risk of hip fracture was only slightly weakened by adjustments for plasma levels of vitamin B12 and folate.

CONCLUSIONS

tHcy seems to be a predictor for hip fracture among elderly men and women. Folate was a predictor among women only, whereas vitamin B12 and MTHFR genotype did not predict hip fracture. Our data corroborate the hypothesis that homocysteine may play a role in the pathogenesis of osteoporotic fractures.

Impact of genetic variation on metabolic response of bone to diet

There is compelling evidence to suggest that both the development of bone to peak bone mass at maturity and subsequent loss depend on the interaction between genetic, hormonal, environmental and nutritional factors. The major part (≤80%) of the age-specific variation in bone turnover and bone density is genetically determined. However, the notion of genetic determinant is of little value unless the specific genes that are involved can be identified. Most work in this area of osteoporosis research has focused on the candidate gene approach, which has identified several candidate genes for osteoporosis, including genes encoding the vitamin D receptor (VDR), oestrogen receptors (α and β), apolipoprotein E, collagen type I α 1 and methylenetetrahydrofolate reductase, amongst many others. However, in general, findings from numerous studies of the association between such genes and various bone variables have been inconsistent. In addition to possible gene—gene interactions it is likely that there are interactions between these genes and certain environmental factors, especially nutrition, that may mediate expression of bone-related phenotypes. While these potential interactions add a level of complexity to our understanding of these apparent genetic effects on bone, identification of a role for genetic factors without knowledge of their interaction with nutrients can do little to advance prevention and treatment of osteoporosis. This information is especially important because, unlike genotype, diet and nutrition can be modified. The aim of the present review is to critically evaluate current knowledge relating to candidate genes for osteoporosis, with particular emphasis on their interaction with nutrients and dietary factors in determining bone health.

Association of the methylenetetrahydrofolate reductase C677T polymorphism and fracture risk in Chinese postmenopausal women

Osteoporotic fractures are a leading cause of disability and, indirectly, of death in the elderly population. Previous studies have shown that homocysteine level and the C677T polymorphism in the gene encoding methylenetetrahydrofolate reductase (MTHFR) may be involved in the development of osteoporosis and its related fracture in European populations. The aim of this study was to verify the association of this polymorphism with bone mineral density (BMD) and fractures in our 1899 Chinese postmenopausal women. The C677T T allele frequency in this population was 39.2%. The distribution of the MTHFR genotypes followed the Hardy-Weinberg equilibrium. BMD at total body, total hip or femoral neck did not significantly vary with MTHFR C677T genotype. The T allele carrier tended to have higher risk of having osteoporosis or osteopenia, but the difference was statistically insignificant. However, Poisson regression analysis revealed that the T allele carriers had an increased risk of fractures (RR=1.7, 95% CI=1.1-2.7, p=0.01) which occurred before or after menopause. As far as fracture incidence after menopause was concerned, the CT or TT genotype had more than twice the risk of the CC genotype (RR=2.5, 95% CI=1.2-4.9, p=0.009). This association was independent of age, physical activity, occupation, passive smoking, height, weight, years since menopause, and total hip BMD. Our data show that the MTHFR C677T polymorphism is an independent predictor of fracture risk, although it only had a weak effect on BMD. Further study on the mechanistic role that this polymorphism plays in the development of fractures may lead to better understanding of the etiology of osteoporotic fracture.

The association of homocysteine and its determinants MTHFR genotype, folate, vitamin B12 and vitamin B6 with bone mineral density in postmenopausal British women

We studied the association between plasma total homocysteine (tHcy), its determinants folate, vitamin B(12), vitamin B(6) and MTHFR genotype, and bone mineral density (BMD) in 328 postmenopausal British women. When the subjects were assigned to one of 3 groups (control, osteopenic or osteoporotic) according to their BMD at the os calcis, those in the osteoporotic group had, compared with the controls, a significantly lower serum folate concentration, a significantly higher % of current smokers and a significantly higher incidence of recent fracture. In the population as a whole, we found significant associations of BMD with tHcy (r=-0.130, p=0.033, log tHcy) and folate (r=0.132, p=0.025, log folate). The association of folate with BMD was maintained after correction for age, weight and height (r=0.124, p=0.042, log folate), but the association of tHcy with BMD weakened after correction for age, weight, height and creatinine (r=-0.117, p=0.059, log tHcy). Vitamins B(12) and B(6) were not associated with BMD, but were significantly associated with tHcy, vitamin B(12) (r=-0.34, p<0.0001), vitamin B(6) (r=-0.16, p=0.007), as was folate (r=-0.41, p<0.0001). There was an increasing frequency of the MTHFR TT genotype across the 3 BMD groups, but this did not attain significance. Individuals with the TT genotype had significantly higher plasma tHcy but there was no difference between the genotypes (CC, CT, TT) for folate or BMD. Smoking was associated with a highly significant reduction in BMD and lower weight, and a significant reduction in circulating folate and vitamin B(6) concentrations, but no change in tHcy or vitamin B(12) concentrations when compared with non-smokers. We conclude that low serum folate is a significant risk factor for osteoporosis, with plasma tHcy having a lesser effect. Both vitamins B(12) and B(6), by acting through tHcy, may also have an effect on the skeleton, albeit a weaker one than folate. Cigarette smoking is a strong determinant of BMD, and may act through effects on folate and vitamin B(6).

MTHFR polymorphism and bone mineral density: meta-analysis of published studies

The C677T (rs1801133) polymorphism of methylenetetrahydrofolate reductase (MTHFR) has been associated with bone status in some studies, but the results have been mixed. In order to have a better understanding of this issue, we performed a meta-analysis of studies about the association of the C677T polymorphism and bone mineral density (BMD). Eight studies analyzed the relationship with spine BMD. When their results were combined, individuals with TT genotype showed a small but significantly reduced BMD compared to those with TC and CC genotypes. The weighted mean difference (WMD) was 18.0 mg/cm2 (P = 0.001, 95% confidence interval [CI] 7.1-28.9), without statistical evidence for between-study heterogeneity (P = 0.28, I2 = 17%). Six studies analyzed femoral neck BMD. A test for heterogeneity was significant (P = 0.03, I2 = 56%). Individuals with TT alleles tended to have somewhat lower BMD, but the difference was not statistically significant. In random effects model, the WMD between the TT and TC/CC genotypes was 6.4 mg/cm2 (95% CI -7.8 to 21.2, P = 0.36). Total hip BMD was measured in four studies. They showed a significantly lower BMD in subjects with TT alleles: WMD 19.7 (95% CI 5.3-34.1) mg/cm2, P = 0.007, in comparison with TC/CC subjects. When we considered only studies on women, the WMD in BMD between TT and TC/CC genotypes was significant at the spine (22.1 mg/cm2, 95% CI 8.6-35.6; P = 0.001) and the femoral neck (15.5 mg/cm2, 95% CI 4.3-26.7; P = 0.007). There was no evidence for heterogeneity. The small number of studies did not allow a meaningful sex-stratified analysis of total hip BMD or a separate analysis of male data. In conclusion, the C677T polymorphism of the MTHFR gene is associated with small differences in BMD, at least in women.

Molecular genetic studies of gene identification for osteoporosis: a 2004 update

This review summarizes comprehensively the most important and representative molecular genetics studies of gene identification for osteoporosis published up to the end of December 2004. It is intended to constitute a sequential update of our previously published review covering the available data up to the end of 2002. Evidence from candidate gene association studies and genome-wide linkage studies in humans, as well as quantitative trait locus mapping animal models are reviewed separately. Studies of transgenic and knockout mice models relevant to osteoporosis are summarized. An important extension of this update is incorporation of functional genomic studies (including DNA microarrays and proteomics) on osteogenesis and osteoporosis, in light of the rapid advances and the promising prospects of the field. Comments are made on the most notable findings and representative studies for their potential influence and implications on our present understanding of genetics of osteoporosis. The format adopted by this review should be ideal for accommodating future new advances and studies.

The association between atopy and factors influencing folate metabolism: is low folate status causally related to the development of atopy?

BACKGROUND

Deficiency of folate has been associated with several disorders characterized by enhanced activation of the cellular immune system (non-allergic th1 type immune response). Whether folate status is also associated with atopic disease (allergic th2 type immune response) is unknown. We aimed at examining the association between atopy and markers of impaired folate metabolism, i.e. MTHFR(C677T) genotype, plasma total homocysteine, and dietary intakes of methionine, folates, and vitamins B12, B6, and B2.

METHODS

Cross-sectional population-based study of 1,671 male and female residents of Copenhagen County, Denmark, aged 30-60 years participating in a health examination during 1999-2001. Atopy was defined as positive levels of specific IgE against a panel of inhalant allergens. MTHFR(C677T) genotype was determined by PCR followed by restriction fragment length polymorphism analyses. Total homocysteine was measured by fluorescent polarization immunoassay. Dietary vitamin intakes were estimated from a semi-quantitative food frequency questionnaire.

RESULTS

The prevalence of atopy was associated with MTHFR(C677T) genotype. TT individuals had a significantly higher risk of atopy compared with CC/CT individuals [odds ratio 1.76, 95% confidence interval (95% CI) 1.19-2.60]. Additionally, gene-diet interaction effects were identified. Dietary markers were negatively associated with risk of atopy in persons with the TT genotype. Total homocysteine was not related to atopy (odds ratio per 5 mumol/l = 1.12, 95% CI 0.98-1.29).

CONCLUSIONS

The results suggest that an impaired folate metabolism may be causally related to the development of atopy.

MTHFR c.677C>T polymorphism as an independent predictor of peak bone mass in Danish men--results from the Odense Androgen Study

The MTHFR c.677C>T polymorphism has been shown to have significant effects on skeletal health in middle-aged to elderly women and men. Despite an accumulating amount of data on MTHFR genetics and the association between homocysteine levels and fracture, it remains unknown if MTHFR c.677C>T genotype affects bone mineral accretion in youth or bone loss in adulthood. The purpose of this cross-sectional study was to examine the effects of this common allelic polymorphism on peak bone mass and bone turnover. We performed MTHFR genotyping in 780 healthy Danish men, aged 20 to 29 years, participating in the Odense Androgen Study. BMD at the spine, hip and whole-body was measured using a Hologic QDR-4500 densitometer. Genotype frequencies were compatible with Hardy-Weinberg equilibrium. Spine BMD was significantly associated with genotype, with a decrease in BMD of 0.20 SD for each copy of the T-allele. Effects were independent of age, BMI, smoking and serum levels of vitamin D and IGF-I. Associations with BMD of the hip and whole body were short of statistical significance. MTHFR genotype showed no association with the bone turnover markers 1-CTP, bone specific alkaline phosphatase or osteocalcin. In conclusion, significant skeletal effects of this common polymorphism were present at the lumbar spine in men at the age of 25 years.

Association of PLOD1 polymorphisms with bone mineral density in a population-based study of women from the UK

The PLOD1 gene is situated within a quantitative trait locus for regulation of bone mineral density (BMD) on chromosome 1p36 and is a strong functional candidate for the regulation of BMD and bone quality. PLOD1 encodes the enzyme procollagen-lysine, 2-oxoglutarate 5-dioxegenase (lysyl hydroxylase; EC 1.14.11.4), which catalyses the hydroxylation of lysine residues during the posttranslational modification of type I collagen, the major protein of bone. We investigated the role of PLOD1 as a genetic determinant of osteoporosis by studying two coding polymorphisms located in exon 3 of the PLOD1 gene in relation to BMD and bone loss in a population-based cohort of 678 Scottish women. We observed a significant association between lumbar spine (LS) BMD and a polymorphism at nucleotide 386 (G386A) of PLOD1, which results in an alanine-threonine amino acid change at codon 99 (A99T). Heterozygotes for G386A had significantly reduced LS-BMD when compared with the other genotype groups, and the difference remained significant after correcting for confounding factors. A similar association was observed between LS-BMD and a conservative polymorphism at position 385 (C385T), but this was in strong linkage disequilibrium (LD) with G386A. There was no evidence for an allele dose effect for either polymorphism, and the strongest association was observed in heterozygotes. No association was found between PLOD1 alleles and femoral-neck BMD or bone loss, but the hydroxylysylpyridinoline to lysylpyridinoline ratio was significantly increased in G386A heterozygotes compared with other genotype groups, suggesting a functional effect of this polymorphism on enzyme activity. Our findings show that heterozygosity for the A99T variant of PLOD1 is associated with reduced LS-BMD and an altered ratio of hydroxylysylpyridinoline to lysylpyridinoline. Whilst further studies will be required to confirm and extend these observations, our studies raise the possibility that A99T heterozygosity might affect lysyl hydroxylase function and regulate bone mass.

Genetics of osteoporosis

Genetic factors play an important role in regulating bone mineral density and other phenotypes relevant to the pathogenesis of osteoporosis such as ultrasound properties of bone, skeletal geometry, and bone turnover. Progress has been made in identifying quantitative traits for regulation of bone mineral density by linkage studies in man and mouse, but relatively few causal genes have been identified. Dramatic progress has been made in identifying the genes responsible for monogenic bone diseases and it appears that polymorphisms in many of these genes also play a role in regulating bone mineral density in the general population. Advances in knowledge about the genetic basis of osteoporosis and other bone diseases offer the prospect of developing new markers for assessment of fracture risk and the identification of novel molecular targets for the design of new drug treatments for osteoporosis.

Homocysteine and vitamin B12 status relate to bone turnover markers, broadband ultrasound attenuation, and fractures in healthy elderly people

Hyperhomocysteinemia may contribute to the development of osteoporosis. The relationship of Hcy and vitamin B12 with bone turnover markers, BUA, and fracture incidence was studied in 1267 subjects of the Longitudinal Aging Study Amsterdam. High Hcy and low vitamin B12 concentrations were significantly associated with low BUA, high markers of bone turnover, and increased fracture risk.

INTRODUCTION

Hyperhomocysteinemia may contribute to the development of osteoporosis. Vitamin B12 is closely correlated to homocysteine (Hcy). The main objective of our study was to examine the association of Hcy and vitamin B12 status and the combined effect of these two with broadband ultrasound attenuation (BUA), bone turnover markers, and fracture.

MATERIALS AND METHODS

Subjects were 615 men and 652 women with a mean age of 76 +/- 6.6 (SD) years of the Longitudinal Aging Study Amsterdam (LASA). At baseline (1995/1996), blood samples were taken after an overnight fast for dairy products. Plasma Hcy was measured with IMx, serum vitamin B12 with competitive immunoassay (IA) luminescence, serum osteocalcin (OC) with immunoradiometric assay (IRMA), and urinary excretion of deoxypyridinoline (DPD) with competitive IA and corrected for creatinine (Cr) concentration. CVs were 4%, 5%, 8%, and 5%, respectively. BUA was assessed in the heel bone twice in both the right and left calcaneus. Mean BUA value was calculated from these four measurements. CV was 3.4%. After baseline measurements in 1995, a 3-year prospective follow-up of fractures was carried out until 1998/1999. Subjects were grouped by using two different approaches on the basis of their vitamin B12 concentration, normal versus low (<200 pM) or lowest quartile (Q1) versus normal quartiles (Q2-Q4), and Hcy concentration, normal versus high (>15 microM) or highest quartile (Q4) versus normal quartiles (Q1-Q3). Analysis of covariance was performed to calculate mean values of BUA, OC, and DPD/Cr(urine) based on the specified categories of Hcy and vitamin B12 and adjusted for several confounders (potential confounders were age, sex, body weight, body height, current smoking [yes/no], mobility, cognition). The relative risk (RR) of any fracture was assessed with Cox regression analysis. Quartiles were used when Hcy and vitamin B12 were separately studied in their relationship with fracture incidence.

RESULTS

Fourteen percent of the men and 9% of the women had high Hcy (>15 microM) and low vitamin B12 (<200 pM) concentrations. Women with vitamin B12 levels <200 pM and Hcy concentrations >15 microM had lower BUA, higher DPD/Cr, and higher OC concentrations than their counterparts. In men, no differences were found between the different Hcy and vitamin B12 categories in adjusted means of BUA, OC, or DPD/Cr(urine). Twenty-eight men and 43 women sustained a fracture during the 3-year follow-up period. The adjusted RR for fractures (95% CI) for men with high Hcy and/or low vitamin B12 concentrations was 3.8 (1.2-11.6) compared with men with normal Hcy and vitamin B12 concentrations. Women with high Hcy and/or low vitamin B12 concentrations had an adjusted RR for fractures of 2.8 (1.3-5.7).

CONCLUSIONS

High Hcy and low vitamin B12 concentrations were significantly associated with low BUA, high markers of bone turnover, and increased fracture risk.

Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism is associated with osteoporotic vertebral fractures, but is a weak predictor of BMD

Osteoporosis is a common disease with a strong genetic component. Linkage studies have suggested linkage between BMD and loci on chromosome 1. The MTHFR gene is located on chromosome 1. MTHFR catalyzes the conversion of 5,10-methylenetetrahydrofolate to 5-methylenetetrahydrofolate, which is used for homocysteine methylation to methionine. The rare genotype (TT) of the C677T polymorphism has previously been demonstrated to be associated with increased plasma homocysteine levels in individuals with inadequate plasma folate levels. Recently, the TT genotype has been found to be associated with reduced bone mass. We therefore examined if the C677T polymorphism in the MTHFR gene is associated with changes in bone mass and risk of osteoporotic fractures in 388 osteoporotic patients and 336 normal individuals. The distributions of the genotypes CC, CT and TT in women with osteoporotic vertebral fractures and normal controls were 43.5%, 42.2% and 14.3% and 52.0%, 42.0% and 8.0%, respectively, chi2 = 5.62, P = 0.06. Since studies of the functionality of this polymorphism have revealed that only the TT genotype is associated with biochemical changes, we also compared the prevalence of the TT genotype versus the CT- and CC genotypes in patients and controls and found that the TT genotype is significantly more common in women with vertebral fractures (14.3%) compared with normal controls (8.0%), chi2 = 4.31, P < 0.05. Logistic regression analysis demonstrated that vertebral fractures were significantly associated with BMD (lumbar spine) and height but only marginally with the MTHFR genotype (P = 0.06). Multiple linear regression analysis revealed that weight, age and the MTHFR polymorphism were predictors of lumbar spine BMD in women. However, age- and gender-corrected BMD of the lumbar spine and the hip was not significantly different between MTHFR genotypes. Furthermore, individuals with the TT genotype did not have BMD significantly lower than the combined group of individuals with the CT- or CC genotypes. In conclusion, we have demonstrated that the rare TT genotype of the C677T polymorphism in the MTHFR gene is associated with increased risk of osteoporotic fractures in women and a weak predictor of lumbar spine BMD.

Are effects of MTHFR (C677T) genotype on BMD confined to women with low folate and riboflavin intake? Analysis of food records from the Danish osteoporosis prevention study

We have previously found BMD and fracture risk to be significantly associated with the MTHFR (C677T) polymorphism in healthy postmenopausal women in the first years after menopause. Since then, other cohort studies have suggested that sufficient intake of riboflavin and/or folate may have the potential to prevent development of low BMD in women with the TT genotype. This could to some extent explain why this polymorphism is associated with low BMD or fracture in some study populations and not in others. It would also indicate that fractures associated with the TT genotype could be preventable by vitamin B supplementation. We have, therefore, reviewed baseline food record data from our original study to determine if BMD and fracture associations with the MTHFR genotype depended on the intake of folate, riboflavin, or other members of the vitamin B complex, associated with homocysteine metabolism. We analyzed genotype, BMD, and dietary records from 1700 healthy postmenopausal women who participated in the DOPS study. For the assessment of fracture risk, we used longitudinal observations from 854 women in the control group who remained compliant with their initial allocation of no treatment. Riboflavin intake was significantly correlated with femoral neck (FN) BMD in women with the TT genotype (r = 0.24, P < 0.01). FN and lumbar spine (LS) BMD were only associated with the MTHFR genotype in the lowest quartile of riboflavin intake. At the FN, similar threshold effects were shown for folate, vitamin B12, and vitamin B6. Among these vitamin B complex members, stepwise regression analysis identified riboflavin as the only significant predictor of FN BMD in the TT genotype. In conclusion, we confirm reports that BMD in the MTHFR TT genotype is only significantly reduced in the lowest quartile of riboflavin, B12, B6, and folate intake, at least at the time of menopause. Vitamin B supplementation would only be expected to benefit BMD in about 2% of the population, i.e., those with the TT genotype and low vitamin B intake.

Homocysteine and Osteoporotic Fracture Risk: A Potential Role for B Vitamins

Hyperhomocysteinemia (elevated plasma homocysteine levels) has been linked to increased risk of neural tube defects, cardiovascular disease, Alzheimer's dementia, pregnancy complications, and inflammatory bowel disease. Evidence for a role of hyperhomocysteinemia in the etiology of osteoporosis has recently been strengthened by the findings of two separate studies, which both reported that high homocysteine levels significantly increased risk of osteoporotic fracture. While the etiology of hyperhomocysteinemia is considered to be multifactorial (including genetic, nutritional, and lifestyle factors), a deficiency of one or more B vitamins certainly has a role. These vitamins are involved in the metabolism and clearance of homocysteine, and thus may have a protective effect against osteoporotic fracture risk.

Methylenetetrahydrofolate reductase polymorphism interacts with riboflavin intake to influence bone mineral density

Bone mineral density is a complex trait regulated by an interaction between genetic and environmental factors. Recent studies have identified a functional polymorphism affecting codon 677 of the methylenetetrahydrofolate reductase (MTHFR) gene that is associated with reduced bone mineral density (BMD) in Japanese and Danish postmenopausal women and increased risk of fracture in elderly Danish women. Since dietary B vitamins can influence circulating homocysteine (tHcy) levels, we examined the relationship among MTHFR genotype, B complex vitamins (folate, vitamin B12, vitamin B6 and riboflavin), BMD, and rate of change in BMD in a longitudinal study of 1241 Scottish women aged 45-54 years, at the time of initial study, who were followed up for a mean (SD) of 6.6 (0.7) years. There was no significant association between BMD and either MTHFR genotype or B complex vitamins when examined separately. However, we detected a significant interaction among quartile of energy-adjusted riboflavin intake, MTHFR 'TT' genotype, and BMD (P = 0.01 for baseline FN BMD, P = 0.02 for follow-up FN BMD). Increasing dietary riboflavin intake correlated with LS BMD and FN BMD in homozygotes for the MTHFR 'T' allele, which remained significant for FN after adjustment for confounders (r = 0.192, P = 0.036 for baseline; r = 0.186, P = 0.043 at follow-up) but not in the other genotypes. This raises the possibility that riboflavin intake and MTHFR genotype might interact to regulate BMD. Further work is required to determine if this association holds true for other populations and ethnic groups.

Association of plasma folate, plasma total homocysteine, but not methylenetetrahydrofolate reductase C667T polymorphism, with bone mineral density in postmenopausal Iranian women: a cross-sectional study

Polymorphisms of methylenetetrahydrofolate reductase (MTHFR) have been well documented to cause hyperhomocysteinemia, and recent studies suggest an association of C677T mutation of methylenetetrahydrofolate reductase with low bone mineral density (BMD). In this study, the association of plasma total homocysteine (Hcy), plasma folate, and vitamin B12 as well as methylenetetrahydrofolate reductase C667T polymorphism with bone mineral density at neck of femur and lumbar spine in 271 postmenopausal Iranian women was investigated. Bone mineral density was measured by dual-energy X-ray absorptiometry. Restriction fragment length polymorphism was used for genotyping the methylenetetrahydrofolate reductase polymorphism. Plasma total homocysteine, plasma folate, and vitamin B12 were also determined. The bone mineral densities at the neck of femur and lumbar spine together with other clinical characteristics among methylenetetrahydrofolate reductase genotypes (CC, CT, and TT) were examined. Bone mineral densities at both neck of femur (r = -0.18, P = 0.003) and lumbar spine (r = -0.16, P = 0.01) were significantly and negatively correlated with the logarithm of plasma total homocysteine. Bone mineral density at the lumbar spine was also significantly and positively associated with plasma folate (r = 0.14, P = 0.02). However, no correlation between methylenetetrahydrofolate reductase polymorphism with bone mineral density at neck of femur (r = -0.01, P = 0.81) and lumbar spine (r = -0.04, P = 0.51) was observed. The negative association of plasma total homocysteine with bone mineral density was no longer significant when adjusted for folate and vitamin B12. Plasma folate and age were the main predictors of plasma total homocysteine explaining 15.3% and 5.2% of the variance of plasma total homocysteine, respectively. Methylenetetrahydrofolate reductase polymorphism, however, was not associated with plasma folate (r = 0.086, P = 0.17) or vitamin B12 (r = 0.05, P = 0.4). Plasma folate was one of the main predictors explaining 3.0% and 1.7% of variance of the bone mineral density at femoral neck and lumbar spine, respectively. Results from this study suggest hyperhomocysteinemia as a result of folate deficiency, but not methylenetetrahydrofolate reductase polymorphism, is independently associated with low bone mineral density and may contribute to the pathogenicity of osteoporosis in postmenopausal Iranian women.

Homocysteine as a predictive factor for hip fracture in older persons

BACKGROUND

The increased prevalence of osteoporosis among people with homocystinuria suggests that a high serum homocysteine concentration may weaken bone by interfering with collagen cross-linking, thereby increasing the risk of osteoporotic fracture. We examined the association between the total homocysteine concentration and the risk of hip fracture in men and women enrolled in the Framingham Study.

METHODS

We studied 825 men and 1174 women, ranging in age from 59 to 91 years, from whom blood samples had been obtained between 1979 and 1982 to measure plasma total homocysteine. The participants in our study were followed from the time that the sample was obtained through June 1998 for incident hip fracture. Sex-specific, age-adjusted incidence rates of hip fracture were calculated for quartiles of total homocysteine concentrations. Cox proportional-hazards regression was used to calculate hazard ratios for quartiles of homocysteine values.

RESULTS

The mean (+/-SD) plasma total homocysteine concentration was 13.4+/-9.1 micromol per liter in men and 12.1+/-5.3 micromol per liter in women. The median duration of follow-up was 12.3 years for men and 15.0 years for women. There were 41 hip fractures among men and 146 among women. The age-adjusted incidence rates per 1000 person-years for hip fracture, from the lowest to the highest quartile for total homocysteine, were 1.96 (95 percent confidence interval, 0.52 to 3.41), 3.24 (0.97 to 5.52), 4.43 (1.80 to 7.07), and 8.14 (4.20 to 12.08) for men and 9.42 (5.72 to 13.12), 7.01 (4.29 to 9.72), 9.58 (6.42 to 12.74), and 16.57 (11.84 to 21.30) for women. Men and women in the highest quartile had a greater risk of hip fracture than those in the lowest quartile--the risk was almost four times as high for men and 1.9 times as high for women.

CONCLUSIONS

These findings suggest that the homocysteine concentration, which is easily modifiable by means of dietary intervention, is an important risk factor for hip fracture in older persons.

Effect of lifestyle factors on plasma total homocysteine concentrations in relation to MTHFR(C677T) genotype. Inter99 (7)

OBJECTIVE

To examine the associations between various lifestyle factors--smoking habits, physical activity, dietary habits, coffee, tea, and alcohol consumption--and homocysteine (tHcy) in relation to MTHFR(C677T) genotype.

DESIGN

Cross-sectional population-based study.

SETTING

Residents of Copenhagen County, Denmark.

SUBJECTS

A random sample of 6457 men and women aged 30-60 years drawn from the Civil Registration System and invited to a health examination in 1999-2001. A total of 2788 participants were included in the statistical analysis.

MAIN OUTCOME MEASURES

tHcy was measured using a Fluorescent Polarization Immuno Assay. MTHFR-genotype was determined by PCR and RFLP analysis. Information about lifestyle factors was obtained from a self-administered questionnaire.

RESULTS

Daily smoking, less healthy dietary habits, and coffee drinking were associated with elevated tHcy concentrations independent of other determinants. Wine consumption was related to tHcy in a J-shaped manner, whereas beer consumption was negatively associated with tHcy after multiple adjustments. Interaction was observed between smoking status and MTHFR-genotype, smoking status and sex, and beer consumption and age. The effect of smoking was more pronounced in persons with the TT genotype and in women. The effect of beer consumption was more pronounced at younger than at older ages.

CONCLUSIONS

Smoking status, dietary habits, coffee intake, wine, and beer consumption were major lifestyle determinants of tHcy. Changes in these lifestyle factors may reduce tHcy concentrations, thereby lowering cardiovascular risk in the general population.

SPONSORSHIP

Danish Medical Research Council, Danish Centre for Evaluation and Health Technology Assessment, and Danish Heart Foundation.

Association of a common polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene with bone phenotypes depends on plasma folate status

A study of a polymorphism in the MTHFR gene, plasma folate, and bone phenotypes in 1632 individuals revealed that the genotype effect on BMD and quantitative ultrasound was dependent on the level of folate. Our findings support the hypothesis that the association between an MTHFR polymorphism and bone phenotypes depends on folate status.

INTRODUCTION

Genome-wide screens using quantitative ultrasound (QUS) and BMD phenotypes have shown suggestive linkage on chromosome 1pter-1p36.3, a region containing the methylenetetrahydrofolate reductase (MTHFR) gene. Individuals homozygous (TT) for the MTHFR C677T polymorphism who have low plasma folate concentrations exhibit elevated plasma homocysteine (tHcy) concentrations that may compromise bone quality. We hypothesized that folate status might modify an association between the C677T polymorphism and bone, possibly by influencing homocysteine concentrations.

MATERIALS AND METHODS

QUS (broadband ultrasound attenuation [BUA], speed of sound, and quantitative ultrasound index) of the heel and BMD of the hip and spine were measured in 1632 male and female members of the Framingham Offspring Study (1996-2001). Participants were assessed for plasma folate concentration and genotyped for the MTHFR C677T polymorphism. TT participants were compared with individuals in the CC + CT group using analysis of covariance.

RESULTS

Adjusted mean QUS and BMD measures did not differ between C677T groups. Although all participants with plasma folate concentrations > or =4 ng/ml had approximately 2% higher QUS and BMD than those with folate <4 ng/ml, the association disappeared after controlling for tHcy. Suggestive interactions between folate status and the C677T group (CC + CT versus TT) were found for hip BMD (p < or = 0.05) and BUA (p = 0.11). Compared with CC + CT participants, TT individuals had lower mean BUA (p = 0.06) and Ward's area BMD (p = 0.08) within the folate <4 ng/ml group and significantly higher hip BMD (p < or = 0.05) within the folate > or =4 ng/ml group. For both folate groups, TT participants had higher age-adjusted mean plasma tHcy versus CC + CT participants. Controlling for tHcy in these models did not affect the statistical significance of the interaction effects.

CONCLUSIONS

Our findings support the hypothesis that the association between the C677T MTHFR polymorphism and bone phenotypes depends on folate status. The mechanism mediating the association, however, remains unclear, but may be partially caused by homocysteine effects on bone.

A common methylenetetrahydrofolate reductase (C677T) polymorphism is associated with low bone mineral density and increased fracture incidence after menopause: longitudinal data from the Danish osteoporosis prevention study

A polymorphism in the gene encoding methylenetetrahydrofolate reductase (MTHFR) has recently been associated with bone mineral density (BMD) in postmenopausal Japanese women. It is not known whether this effect is also present in European populations and whether it is caused by lower peak bone mass or accelerated postmenopausal bone loss. MTHFR genotyping was done in 1748 healthy postmenopausal Danish women participating in a prospective study of risk factors for osteoporosis. At the time of enrollment, 3-24 months after last menstrual period, the less prevalent genotype (TT, 8.7% of the population) was associated with significantly lower BMD at the femoral neck (ANOVA, p < 0.05), total hip (p < 0.01), and spine (p < 0.05 adjusted for lifestyle covariates, p = 0.06 without adjustment). The mean difference was between 0.1 and 0.3 SD, depending on measurement site. MTHFR genotype added significantly to prediction of BMD by weight and age. Fracture incidence was increased more than 2-fold in subjects with the TT genotype (risk ratio [RR], 2.6; 95% CI 1.2-5.6). This remained significant when the Cox analysis was controlled for BMD (RR, 2.4; 95% CI 1.1-5.2). No differences in serum osteocalcin, bone-specific alkaline phosphatase, and 25-OH-vitamin D were found between genotypes. The response to hormone replacement therapy (HRT) did not differ, but the association of the TT genotype with reduced BMD was maintained at the total hip after 5 years of HRT. The MTHFR TT genotype is associated with low BMD and increased fracture incidence in early postmenopausal women.