A gene conferring susceptibility to type 2 diabetes in conjunction with obesity is located on chromosome 18p11

CIDE Proteins in Human Health and Disease

Cell death-Inducing DNA Fragmentation Factor Alpha (DFFA)-like Effector (CIDE) proteins have emerged as lipid droplet-associated proteins that regulate fat metabolism. There are three members in the CIDE protein family—CIDEA, CIDEB, and CIDEC (also known as fat-specific protein 27 (FSP27)). CIDEA and FSP27 are primarily expressed in adipose tissue, while CIDEB is expressed in the liver. Originally, based upon their homology with DNA fragmentation factors, these proteins were identified as apoptotic proteins. However, recent studies have changed the perception of these proteins, redefining them as regulators of lipid droplet dynamics and fat metabolism, which contribute to a healthy metabolic phenotype in humans. Despite various studies in humans and gene-targeting studies in mice, the physiological roles of CIDE proteins remains elusive. This review will summarize the known physiological role and metabolic pathways regulated by the CIDE proteins in human health and disease.

A mosaic intragenic microduplication of LAMA1 and a constitutional 18p11.32 microduplication in a patient with keratosis pilaris and intellectual disability

The application of array-based comparative genomic hybridization and next-generation sequencing has identified many chromosomal microdeletions and microduplications in patients with different pathological phenotypes. Different copy number variations are described within the short arm of chromosome 18 in patients with skin diseases. In particular, full or partial monosomy 18p has also been associated with keratosis pilaris. Here, for the first time, we report a young male patient with intellectual disability, diabetes mellitus (type I), and keratosis pilaris, who exhibited a de novo 45-kb microduplication of exons 4-22 of LAMA1, located at 18p11.31, and a 432-kb 18p11.32 microduplication of paternal origin containing the genes METTL4, NDC80, and CBX3P2 and exons 1-15 of the SMCHD1 gene. The microduplication of LAMA1 was identified in skin fibroblasts but not in lymphocytes, whereas the larger microduplication was present in both tissues. We propose LAMA1 as a novel candidate gene for keratosis pilaris. Although inherited from a healthy father, the 18p11.32 microduplication, which included relevant genes, could also contribute to phenotype manifestation.

Psoriasis and comorbid diseases: Epidemiology

Psoriasis is a common chronic inflammatory disease of the skin that is increasingly being recognized as a systemic inflammatory disorder. Psoriatic arthritis is a well-known comorbidity of psoriasis. A rapidly expanding body of literature in various populations and settings supports additional associations between psoriasis and cardiometabolic diseases, gastrointestinal diseases, kidney disease, malignancy, infection, and mood disorders. The pathogenesis of comorbid disease in patients with psoriasis remains unknown; however, shared inflammatory pathways, cellular mediators, genetic susceptibility, and common risk factors are hypothesized to be contributing elements. As additional psoriasis comorbidities continue to emerge, education of health care providers is essential to ensuring comprehensive medical care for patients with psoriasis.

Genetics of Type 2 Diabetes: It Matters From Which Parent We Inherit the Risk

Type 2 diabetes (T2D) results from a co-occurrence of genes and environmental factors. There are more than 120 genetic loci suggested to be associated with T2D, or with glucose and insulin levels in European and multi-ethnic populations. Risk of T2D is higher in the offspring if the mother rather than the father has T2D. Genetically, this can be associated with a unique parent-of-origin (PoO) transmission of risk alleles, and it relates to genetic programming during the intrauterine period, resulting in the inability to increase insulin secretion in response to increased demands imposed by insulin resistance later in life. Such PoO transmission is seen for variants in the KLF14, KCNQ1, GRB10, TCF7L2, THADA, and PEG3 genes. Here we describe T2D susceptibility genes associated with defects in insulin secretion, and thereby risk of overt T2D. This review emphasizes the need to consider distorted parental transmission of risk alleles by exploring the genetic risk of T2D.

Hypothesis of the neuroendocrine cortisol pathway gene role in the comorbidity of depression, type 2 diabetes, and metabolic syndrome

Depression, type 2 diabetes (T2D), and metabolic syndrome (MetS) are often comorbid. Depression per se increases the risk for T2D by 60%. This risk is not accounted for by the use of antidepressant therapy. Stress causes hyperactivation of the hypothalamic–pituitary–adrenal (HPA) axis, by triggering the hypothalamic corticotropin-releasing hormone (CRH) secretion, which stimulates the anterior pituitary to release the adrenocorticotropin hormone (ACTH), which causes the adrenal secretion of cortisol. Depression is associated with an increased level of cortisol, and CRH and ACTH at inappropriately “normal” levels, that is too high compared to their expected lower levels due to cortisol negative feedback. T2D and MetS are also associated with hypercortisolism. High levels of cortisol can impair mood as well as cause hyperglycemia and insulin resistance and other traits typical of T2D and MetS. We hypothesize that HPA axis hyperactivation may be due to variants in the genes of the CRH receptors (CRHR1, CRHR2), corticotropin receptors (or melanocortin receptors, MC1R-MC5R), glucocorticoid receptor (NR3C1), mineralocorticoid receptor (NR3C2), and of the FK506 binding protein 51 (FKBP5), and that these variants may be partially responsible for the clinical association of depression, T2D and MetS. In this review, we will focus on the correlation of stress, HPA axis hyperactivation, and the possible genetic role of the CRHR1, CRHR2, MCR1–5, NR3C1, and NR3C2 receptors and FKBP5 in the susceptibility to the comorbidity of depression, T2D, and MetS. New studies are needed to confirm the hypothesized role of these genes in the clinical association of depression, T2D, and MetS.

Variation in genes related to hepatic lipid metabolism and changes in waist circumference and body weight

We analysed single nucleotide polymorphisms (SNPs) tagging the genetic variability of six candidate genes (ATF6, FABP1, LPIN2, LPIN3, MLXIPL and MTTP) involved in the regulation of hepatic lipid metabolism, an important regulatory site of energy balance for associations with body mass index (BMI) and changes in weight and waist circumference. We also investigated effect modification by sex and dietary intake. Data of 6,287 individuals participating in the European prospective investigation into cancer and nutrition were included in the analyses. Data on weight and waist circumference were followed up for 6.9 ± 2.5 years. Association of 69 tagSNPs with baseline BMI and annual changes in weight as well as waist circumference were investigated using linear regression analysis. Interactions with sex, GI and intake of carbohydrates, fat as well as saturated, monounsaturated and polyunsaturated fatty acids were examined by including multiplicative SNP-covariate terms into the regression model. Neither baseline BMI nor annual weight or waist circumference changes were significantly associated with variation in the selected genes in the entire study population after correction for multiple testing. One SNP (rs1164) in LPIN2 appeared to be significantly interacting with sex (p = 0.0003) and was associated with greater annual weight gain in men (56.8 ± 23.7 g/year per allele, p = 0.02) than in women (-25.5 ± 19.8 g/year per allele, p = 0.2). With respect to gene-nutrient interaction, we could not detect any significant interactions when accounting for multiple testing. Therefore, out of our six candidate genes, LPIN2 may be considered as a candidate for further studies.

The genetic contribution of CIDEA polymorphisms, haplotypes and loci interaction to obesity in a Han Chinese population

To investigate the association of tag-SNPs and haplotype structures of the CIDEA gene with obesity in a Han Chinese population. Five single nucleotide polymorphisms (SNPs) (rs1154588/V115F, rs4796955/SNP1, rs8092502/SNP2, rs12962340/SNP3 and rs7230480/SNP4) in the CIDEA gene were genotyped in a case-control study. Genotyping was performed using the sequenom matrix-assisted laser desorption/ionization time-of-flight mass spectrometry iPLEX platform. There were significant differences between the obese and control groups in genotype distributions of V115F (P < 0.001), SNP1 (P = 0.006) and SNP2 (P = 0.005). Carriers of V115F-TT, SNP1-GG and SNP2-CC genotypes had a 2.84-fold (95 % CI 1.73-4.66), 2.19-fold (95 % CI 1.09-4.38) and 4.37-fold (95 % CI 1.21-15.08) increased risk for obesity, respectively. Haplotype analysis showed that GTTC (SNP1/SNP2/V115F/SNP4) had 1.41-fold (95 % CI 1.02-1.95) increased risk for obesity; whereas, haplotype TTGC had 0.48-fold (95 % CI 0.24-0.96) decreased risk for obesity. Using the multifactor dimensionality reduction method, the best model including SNP1, SNP2, V115F and SNP4 polymorphisms was identified with a maximum testing accuracy to 59.32 % and a perfect cross-validation consistency of 10/10 (P = 0.011). Logistic analysis indicated that there was a significant interaction between SNP1 and V115F associated with obesity. Subjects having both genotypes of SNP1/GG and V115F/TT were more susceptible to obesity in the Han Chinese population (OR 2.66, 95 %: 1.22-5.80). Genotypes of V115F/TT, SNP1/GG and SNP2/CC and haplotype GTTC of CIDEA gene were identified as risk factors for obesity in the Han Chinese population. The interaction between SNP1 and V115F could play a joint role in the development of obesity.

Association of the cell death-inducing DNA fragmentation factor alpha-like effector A (CIDEA) gene V115F (G/T) polymorphism with phenotypes of metabolic syndrome in a Chinese population

AIMS

The CIDEA gene is involved in energy metabolism and a non-synonymous single nucleotide polymorphism (SNP), V115F (G/T), is a risk factor for obesity in Swedish subjects and metabolic syndrome (MetS) in Japanese subjects. However, the risk allele was a G in Swedish subjects and a T in Japanese subjects. The present study investigated the association between this SNP and MetS in a Chinese population.

METHODS

Three hundred and fifty-one subjects evaluated at the Cardiac Clinic in Xuanwu Hospital for MetS risks were recruited. Anthropometric measurements, blood pressure, fasting blood glucose, and blood lipid levels were determined in addition to the polymorphism.

RESULTS

The proportion of subjects with MetS was significantly higher based on genotype, in the order: GG<GT<TT (p=0.003). In multiple logistic regression analysis, the odds ratios for MetS in the GT and TT genotypes, compared to the referent GG genotype, were 2.26 (p=0.003) and 2.89 (p=0.002), respectively. Similar trends were observed for the related phenotypes of central obesity (GT: OR=2.20, p=0.004; TT: OR=3.31, p=0.002) and dyslipidemia (GT: OR=1.73, p=0.047; TT: OR=2.10, p=0.03).

CONCLUSIONS

The T allele of the CIDEA V115F SNP is a risk factor for MetS and its related phenotypes in a Chinese population.

Direct evidence for susceptibility genes for type 2 diabetes on mouse chromosomes 11 and 14

AIMS/HYPOTHESIS

Diabetogenic loci for type 2 diabetes have been mapped to mouse chromosome (Chr) 11 and 14 in the Nagoya-Shibata-Yasuda (NSY) mouse, an animal model of type 2 diabetes. We aimed to obtain direct evidence of these genes on each chromosome and to clarify their function and interaction in conferring susceptibility to type 2 diabetes.

METHODS

We established three consomic strains homozygous for diabetogenic NSY-Chr11, NSY-Chr14 or both on the control C3H background (C3H-11(NSY), C3H-14(NSY) and C3H-11(NSY)14(NSY), respectively), and monitored diabetes-related phenotypes longitudinally. The glucokinase gene was sequenced as a positional candidate gene on Chr11.

RESULTS

C3H-11(NSY) mice showed hyperglycaemia associated with impaired insulin secretion and age-dependent insulin resistance without obesity. C3H-14(NSY) mice exhibited hyperglycaemia mainly due to insulin resistance, with a slight increase in percentage body fat. C3H-11(NSY)14(NSY) double consomic mice showed marked hyperglycaemia and obesity, which was not observed in single consomic strains. Sequences of the glucokinase gene were allelically variant between NSY and C3H mice.

CONCLUSIONS/INTERPRETATION

These data provide direct evidence that Chr11 and Chr14 harbour major susceptibility genes for type 2 diabetes. These two chromosomes interact to cause more severe hyperglycaemia and obesity, which was not observed with the presence of either single chromosome, indicating different modes of gene-gene interaction depending on the phenotype. Marked changes in the phenotypes retained in the consomic strains will facilitate fine mapping and the identification of the responsible genes and their interaction with each other, other genes and environmental factors.

Genome-wide linkage scans for type 2 diabetes mellitus in four ethnically diverse populations-significant evidence for linkage on chromosome 4q in African Americans: the Family Investigation of Nephropathy and Diabetes Research Group

BACKGROUND

Previous studies have shown that in addition to environmental influences, type 2 diabetes mellitus (T2DM) has a strong genetic component. The goal of the current study is to identify regions of linkage for T2DM in ethnically diverse populations.

METHODS

Phenotypic and genotypic data were obtained from African American (AA; total number of individuals [N] = 1004), American Indian (AI; N = 883), European American (EA; N = 537), and Mexican American (MA; N = 1634) individuals from the Family Investigation of Nephropathy and Diabetes. Non-parametric linkage analysis, using an average of 4404 SNPs, was performed in relative pairs affected with T2DM in each ethnic group. In addition, family-based tests were performed to detect association with T2DM.

RESULTS

Statistically significant evidence for linkage was observed on chromosome 4q21.1 (LOD = 3.13; genome-wide p = 0.04) in AA. In addition, a total of 11 regions showed suggestive evidence for linkage (estimated at LOD > 1.71), with the highest LOD scores on chromosomes 12q21.31 (LOD = 2.02) and 22q12.3 (LOD = 2.38) in AA, 2p11.1 (LOD = 2.23) in AI, 6p12.3 (LOD = 2.77) in EA, and 13q21.1 (LOD = . 2.24) in MA. While no region overlapped across all ethnic groups, at least five loci showing LOD > 1.71 have been identified in previously published studies.

CONCLUSIONS

The results from this study provide evidence for the presence of genes affecting T2DM on chromosomes 4q, 12q, and 22q in AA; 6p in EA; 2p in AI; and 13q in MA. The strong evidence for linkage on chromosome 4q in AA provides important information given the paucity of diabetes genetic studies in this population.

Agreement among type 2 diabetes linkage studies but a poor correlation with results from genome-wide association studies

AIMS/HYPOTHESIS

Little of the genetic basis for type 2 diabetes has been explained, despite numerous genetic linkage studies and the discovery of multiple genes in genome-wide association (GWA) studies. To begin to resolve the genetic component of this disease, we searched for sites at which genetic results had been corroborated in different studies, in the expectation that replication among studies should direct us to the genomic locations of causative genes with more confidence than the results of individual studies.

METHODS

We have mapped the physical location of results from 83 linkage reports (for type 2 diabetes and diabetes precursor quantitative traits [QTs, e.g. plasma insulin levels]) and recent large GWA reports (for type 2 diabetes) onto the same human genome sequence to identify replicated results in diabetes genetic 'hot spots'.

RESULTS

Genetic linkage has been found at least ten times at 18 different locations, and at least five times in 56 locations. All replication clusters contained study populations from more than one ethnic background and most contained results for both diabetes and QTs. There is no close relationship between the GWA results and linkage clusters, and the nine best replication clusters have no nearby GWA result.

CONCLUSIONS/INTERPRETATION

Many of the genes for type 2 diabetes remain unidentified. This analysis identifies the broad location of yet to be identified genes on 6q, 1q, 18p, 2q, 20q, 17pq, 8p, 19q and 9q. The discrepancy between the linkage and GWA studies may be explained by the presence of multiple, uncommon, mildly deleterious polymorphisms scattered throughout the regulatory and coding regions of genes for type 2 diabetes.

Role of pituitary adenylate cyclase-activating polypeptide in the pancreatic endocrine system

In the pancreatic islets, pituitary adenylate cyclase-activating polypeptide (PACAP) is expressed in beta cells and autonomic nerve terminals; the majority of these nerve terminals are parasympathetic. PACAP binds to three types of G protein-coupled receptors (GPCRs): VPAC1 receptors, VPAC2 receptors, and PAC1 receptors. All these receptor types are expressed in pancreatic islets. PACAP stimulates insulin and glucagon secretion. These actions are achieved in part through increased formation of cAMP after activation of adenylate cyclase and in part through increase in cytosolic calcium, achieved through increase in calcium uptake and release from intracellular calcium stores. Deletion of PAC1 receptors or VPAC2 receptors results in impaired insulin secretion and glucose intolerance. Studies in PAC1 receptor gene deleted mice have suggested that PACAP may be of physiological importance in mediating prandial insulin secretion and in contributing to the glucagon response to hypoglycemia. Animal studies have also suggested that activation of the receptors, in particular VPAC2 receptors, may be used as a therapeutic approach for the treatment of type 2 diabetes. Hence, PACAP is an islet neuropeptide with a potential role in islet physiology and as a basis for development of islet-promoting therapy in type 2 diabetes.

Genome-wide linkage and admixture mapping of type 2 diabetes in African American families from the American Diabetes Association GENNID (Genetics of NIDDM) Study Cohort

OBJECTIVE

We used a single nucleotide polymorphism (SNP) map in a large cohort of 580 African American families to identify regions linked to type 2 diabetes, age of type 2 diabetes diagnosis, and BMI.

RESEARCH DESIGN AND METHODS

After removing outliers and problematic samples, we conducted linkage analysis using 5,914 SNPs in 1,344 individuals from 530 families. Linkage analysis was conducted using variance components for type 2 diabetes, age of type 2 diabetes diagnosis, and BMI and nonparametric linkage analyses. Ordered subset analyses were conducted ranking on age of type 2 diabetes diagnosis, BMI, waist circumference, waist-to-hip ratio, and amount of European admixture. Admixture mapping was conducted using 4,486 markers not in linkage disequilibrium.

RESULTS

The strongest signal for type 2 diabetes (logarithm of odds [LOD] 4.53) was a broad peak on chromosome 2, with weaker linkage to age of type 2 diabetes diagnosis (LOD 1.82). Type 2 diabetes and age of type 2 diabetes diagnosis were linked to chromosome 13p (3-22 cM; LOD 2.42 and 2.46, respectively). Age of type 2 diabetes diagnosis was linked to 18p (66 cM; LOD 2.96). We replicated previous reports on chromosome 7p (79 cM; LOD 2.93). Ordered subset analysis did not overlap with linkage of unselected families. The best admixture score was on chromosome 12 (90 cM; P = 0.0003).

CONCLUSIONS

The linkage regions on chromosomes 7 (27-78 cM) and 18p overlap prior reports, whereas regions on 2p and 13p linkage are novel. Among potential candidate genes implicated are TCF7L1, VAMP5, VAMP8, CDK8, INSIG2, IPF1, PAX8, IL18R1, members of the IL1 and IL1 receptor families, and MAP4K4. These studies provide a complementary approach to genome-wide association scans to identify causative genes for African American diabetes.

Ordered stratification to reduce heterogeneity in linkage to diabetes-related quantitative traits

Phenotypic heterogeneity complicates detection of genomic loci predisposing to type 2 diabetes, potentially obscuring or unmasking specific loci. We conducted ordered-subsets linkage analyses (OSAs) for diabetes-related quantitative traits (fasting insulin and glucose, hemoglobin A1c (HbA1c), and 28-year-time-averaged fasting plasma glucose (FPG)) from 330 families of the Framingham Offspring Study. We calculated mean BMI, waist circumference (WC), and a diabetes "age-of-onset score" for each family. We constructed subsets by adding one family at a time in increasing (lean family to obese) or decreasing (obese to lean) adiposity order, or increasing or decreasing propensity to develop diabetes at a younger age, with the OSA LOD reported as the maximum LOD observed in any subset. Permutation P values tested the hypothesis that phenotypic ordering showed stronger linkage than random ordering. On chromosome 1, ordering by increasing family mean WC increased linkage to time-averaged FPG at 256 cM from LOD = 2.4 to 3.5 (permuted P = 0.02) and to HbA1c at 180 cM from LOD = 2.0 to 3.3 (P = 0.01). On chromosome 19, ordering by decreasing WC increased linkage to fasting insulin at 68 cM from LOD = 2.7 to 4.6 (P = 0.002), and ordering by decreasing propensity to develop diabetes at a young age increased linkage to fasting insulin at 73 cM from LOD = 2.7 to 4.0 (P = 0.046). We conclude that chromosomes 1 and 19 could harbor adiposity-interacting diabetes susceptibility genes. Such interactions might also influence trait-locus associations and may be useful to consider in diabetes genome-wide association studies.

Psoriasis and metabolic disease: epidemiology and pathophysiology

PURPOSE OF REVIEW

The scientific literature linking psoriasis to metabolic syndrome, and its components, as well as atherosclerosis and myocardial infarction has rapidly expanded. Increasingly, epidemiological studies are establishing the directionality of these associations and psoriasis' role as an independent risk factor in developing these outcomes.

RECENT FINDINGS

Psoriasis is associated with metabolic syndrome, and its components, such as obesity, diabetes, and hypertension. Obesity has been shown to be an independent risk factor for the development of psoriasis, and is also associated with more severe psoriasis. Psoriasis is associated with diabetes, coronary artery disease, and an increased risk for myocardial infarction independent of traditional risk factors for these disorders. These phenotypically diverse conditions share similar pathologic changes such as chronic inflammation, angiogenesis, oxidative stress, and selected susceptibility genes and loci.

SUMMARY

The broad literature linking psoriasis to metabolic disorders has led to changes in standard of care recommendations for patients with psoriasis. In particular, practitioners are encouraged to screen psoriasis patients, especially when disease is severe, for metabolic disorders and cardiovascular risk factors and institute appropriate prevention strategies. Additional studies investigating the role of psoriasis activity and severity as an independent risk factor for developing metabolic disorders, atherosclerosis, and myocardial infarction and the role of psoriasis treatment in altering the risk of developing these serious morbidities are urgently needed.

Cell death-inducing DNA fragmentation factor alpha-like effector A (CIDEA) gene V115F (G-->T) polymorphism is associated with phenotypes of metabolic syndrome in Japanese men

Cell death-inducing DNA fragmentation factor alpha-like effector A (CIDEA) regulates energy expenditure in the adipose tissue and is implicated in the development of obesity. A single nucleotide polymorphism in the CIDEA gene that causes an amino acid substitution of valine 115 to c(V115F) has recently been shown to be associated with obesity in the Swedish population. Here, we determined the effects of this polymorphism on phenotypes of metabolic syndrome within the Japanese population. Two hundred seventy unrelated Japanese male workers (mean age, 44.5 years) were analyzed in a cross-sectional study. The clinical features regarding metabolic syndrome, as well as CIDEA V115F polymorphism, were determined for each individual. The V115F polymorphism associated with waist circumference and fasting plasma glucose. These parameters were at higher levels in the VF + FF group than in the VV group (P < .05). The VF + FF group compared with the VV group had a higher prevalence for abdominal obesity (odds ratio [OR] = 1.89; 95% confidence interval [CI], 1.03-3.44), high fasting plasma glucose (OR = 2.81; 95% CI, 1.03-7.67), and metabolic syndrome (OR = 3.15; 95% CI, 1.05-9.48). These results suggest that the F allele of the CIDEA gene may serve as a risk factor for phenotypes related to metabolic syndrome in Japanese men.

Quantitative linkage analysis for pancreatic B-cell function and insulin resistance in a large twin cohort

OBJECTIVE

Insulin resistance and disturbed glucose homeostasis are key characteristics of metabolic syndrome, diabetes, and cardiovascular disease. The recent nonlinear computer version of homeostasis model assessment (HOMA)2 provides an appropriate and convenient assessment of glucose metabolism, enabling gene-mapping studies in large population samples.

RESEARCH DESIGN AND METHODS

Fasting insulin and glucose concentration were measured in 758 dizygous and 305 monozygous nondiabetic female pairs from the St. Thomas' U.K. adult twin registry (TwinsUK). Insulin resistance (IR) and pancreatic beta-cell function (BCF) were estimated from this data using the HOMA2 model.

RESULTS

Genome-wide variance component linkage analysis using 2,231 genetic markers identified a highly significant quantitative trait locus for BCF on chromosome 10p15 (logarithm of odds [LOD] 6.2, P = 0.0001), a region recently shown to contain a functional variant for type 1 diabetes. Both BCF and IR suggested a pleiotropic effect on 17q25 (univariate LOD 3.2, P = 0.0012, and 2.38, P = 0.0087; bivariate LOD 2.66), and one additional region showed linkage for IR on chromosome 22q11 (LOD 3.2, P = 0.0016), providing replication and refining previous findings for diabetes and associated traits.

CONCLUSIONS

To our best knowledge, this is the first genome-wide linkage screen for HOMA2 indexes in a large, healthy female sample. These results suggest that loci involved in control of normal glucose homeostasis among nondiabetic individuals might overlap with those involved in the development of diabetes. Linkage replications in independent studies and across populations provide information on important regions of common but potentially heterogeneous variability that can now be used for targeted positional candidate studies.

Genome-wide scan revealed genetic loci for energy metabolism in Hispanic children and adolescents

OBJECTIVE

Genome-wide scans were conducted in search for genetic locations linked to energy expenditure and substrate oxidation in children.

DESIGN

Pedigreed data of 1030 Hispanic children and adolescents were from the Viva La Familia Study which was designed to investigate genetic and environmental risk factors for the development of obesity in Hispanic families. A respiratory calorimeter was used to measure 24-h total energy expenditure (TEE), basal metabolic rate (BMR), sleep metabolic rate (SMR), 24-h respiratory quotient (24RQ), basal metabolic respiratory quotient (BMRQ) and sleep respiratory quotient (SRQ). Protein, fat and carbohydrate oxidation (PROOX, FATOX and CHOOX, respectively) were also estimated. All participants were genotyped for 384 single tandem repeat markers spaced an average of 10 cM apart. Computer program SOLAR was used to perform the genetic linkage analyses.

RESULTS

Significant linkage for TEE was detected on chromosome 1 near marker D1S2841, with a logarithm of the odds (LOD) score of 4.0. SMR, BMRQ and PROOX were associated with loci on chromosome 18, 17 and 9, respectively, with LOD scores of 4.88, 3.17 and 4.55, respectively. A genome-wide scan of SMR per kg fat-free mass (SpFFM) peaked in the same region as SMR on chromosome 18 (LOD, 5.24). Suggestive linkage was observed for CHOOX and FATOX. Several candidate genes were found in the above chromosomal regions including leptin receptor (LEPR).

CONCLUSION

Regions on chromosomes 1, 9, 17 and 18 harbor genes affecting variation in energy expenditure and substrate oxidation in Hispanic children and adolescents.

LPIN2 is associated with type 2 diabetes, glucose metabolism, and body composition

OBJECTIVE

To identify the type 2 diabetes gene located at chromosome 18p11.

RESEARCH DESIGN AND METHODS

We investigated the region in a young genetically isolated population by genotyping 34 single nucleotide polymorphisms (SNPs) in 78 case subjects and 101 control subjects. Two SNPs were selected and followed up in two cohorts. The first cohort came from a general Dutch population. In this cohort, association with type 2 diabetes was investigated using 616 type 2 diabetic case subjects and 2,890 control subjects; association with oral glucose tolerance test data was performed in 361 normoglycemic people. Association with fat distribution was studied in the second replication cohort, consisting of 836 people from the genetically isolated population.

RESULTS

At the initial step, we found that the common C allele of SNP rs3745012 was associated with type 2 diabetes (odds ratio 2.01, P = 0.03). This SNP is located at the 3' untranslated region of the LPIN2 gene, which is a plausible candidate for type 2 diabetes and obesity. In the cohort from the general Dutch population, we demonstrated that rs3745012 interacts with BMI in determination of type 2 diabetes: whereas in subjects with high BMI, the common C allele is associated with type 2 diabetes, the same allele exhibits a neutral or protective effect in lean subjects (P = 0.05 overall effect, P = 0.02 interaction). Most remarkably, rs3745012 strongly affected composite insulin sensitivity index (P = 0.006 for overall effect, P = 0.004 for interaction). In the second replication cohort, we found that the allele C of rs3745012 increases trunk-to-legs fat mass ratio (P = 0.001) and may affect other fat-related measurements.

CONCLUSIONS

rs3745012 SNP of the LPIN2 gene is associated with type 2 diabetes and fat distribution.

An investigation of genome-wide associations of hypertension with microsatellite markers in the family blood pressure program (FBPP)

The Family Blood Pressure Program (FBPP) has data on 387 microsatellite markers in 13,524 subjects from four major ethnic groups. We investigated genetic association with hypertension of the linkage markers. Family-based methods were used to test association of the 387 loci with resting blood pressures (BPs) [systolic blood pressure (SBP) and diastolic blood pressure (DBP)] and the hypertension status (HT). We applied a vote-counting approach to pool results across the three correlated traits, network samples, and ethnic groups to refine the selection of susceptibility loci. The association analyses captured signals missed by previous linkage scans. We found 71 loci associated with at least one of the three traits in at least one of the four ethnic groups at the significance level of 0.01. After validation across multiple samples and related traits, we identified by vote-counting 21 candidate loci for hypertension. Two loci, D3S2459 and D10S1412 confirmed findings in Network-specific linkage scans (GENOA and SAPPHIRe). Many of the candidate loci were reported by others in linkage to BPs, body weight, heart disease, and diabetes. We also observed frequent presence of quantitative trait loci (QTLs) involved in autoimmune and neurological disorders (e.g., NOD2). The vote-counting method of pooling results recognizes the potential that a gene may be involved in varying ways among different samples, which we believe is responsible for identifying genes in the less explored inflammatory pathways to hypertension.

The genetic landscape of type 2 diabetes in mice

Inbred mouse strains provide genetic diversity comparable to that of the human population. Like humans, mice have a wide range of diabetes-related phenotypes. The inbred mouse strains differ in the response of their critical physiological functions, such as insulin sensitivity, insulin secretion, beta-cell proliferation and survival, and fuel partitioning, to diet and obesity. Most of the critical genes underlying these differences have not been identified, although many loci have been mapped. The dramatic improvements in genomic and bioinformatics resources are accelerating the pace of gene discovery. This review describes how mouse genetics can be used to discover diabetes-related genes, summarizes how the mouse strains differ in their diabetes-related phenotypes, and describes several examples of how loci identified in the mouse may directly relate to human diabetes.

Meta-analysis of 23 type 2 diabetes linkage studies from the International Type 2 Diabetes Linkage Analysis Consortium

BACKGROUND

The International Type 2 Diabetes Linkage Analysis Consortium was formed to localize type 2 diabetes predisposing variants based on 23 autosomal linkage scans.

METHODS

We carried out meta-analysis using the genome scan meta-analysis (GSMA) method which divides the genome into bins of approximately 30 cM, ranks the best linkage results in each bin for each sample, and then sums the ranks across samples. We repeated the meta-analysis using 2 cM bins, and/or replacing bin ranks with measures of linkage evidence: bin maximum LOD score or bin minimum p value for bins with p value <0.05 (truncated p value). We also carried out computer simulations to assess the empirical type I error rates of these meta-analysis methods.

RESULTS

Our analyses provided modest evidence for type 2 diabetes-predisposing variants on chromosomes 4, 10, and 14 (using LOD scores or truncated p values), or chromosome 10 and 16 (using ranks). Our simulation results suggested that uneven marker density across studies results in substantial variation in empirical type I error rates for all meta-analysis methods, but that 2 cM bins and scores that make more explicit use of linkage evidence, especially the truncated p values, reduce this problem.

CONCLUSION

We identified regions modestly linked with type 2 diabetes by summarizing results from 23 autosomal genome scans.

A strategy to search for common obesity and type 2 diabetes genes

Worldwide, the incidence of type 2 diabetes is rising rapidly, mainly because of the increase in the incidence of obesity, which is an important risk factor for this condition. Both obesity and type 2 diabetes are complex genetic traits but they also share some nongenetic risk factors. Hence, it is tempting to speculate that the susceptibility to type 2 diabetes and obesity might also partly be due to shared genes. By comparing all of the published genome scans for type 2 diabetes and obesity, five overlapping chromosomal regions for both diseases (encompassing 612 candidate genes) have been identified. By analysing these five susceptibility loci for type 2 diabetes and obesity, using six freely available bioinformatics tools for disease gene identification, 27 functional candidate genes have been pinpointed that are involved in eating behaviour, metabolism and inflammation. These genes might reveal a molecular link between the two disorders.

Linkage and Association Studies of the Susceptibility Genes for Type 2 Diabetes

Type 2 diabetes mellitus (T2DM) is a complex disease characterized by hyperglycemia, insulin resistance, and impaired insulin secretion. T2DM is under strong genetic control. Identification and characterization of genes involved in determining T2DM will contribute to a greater understanding of the pathogenesis of T2DM, and ultimately might lead to the development of better diagnosis, prevention and treatment strategies. Efforts to identify T2DM susceptibility genes have focused on candidate gene approach (association studies) and genome-wide scans (linkage analyses). In this article, we review the current status for mapping and identification of genes for T2DM, with a focus on some promising regions (or genes) and future prospects.

The Genetic Basis of Type 2 Diabetes

Type 2 Diabetes results from a complex physiologic process that includes the pancreatic beta cells, peripheral glucose uptake in muscle, the secretion of multiple cytokines and hormone-like molecules from adipocytes, hepatic glucose production, and likely the central nervous system. Consistent with the complex web of physiologic defects, the emerging picture of the genetics will involve a large number of risk susceptibility genes, each individually with relatively small effect (odds ratios below 1.2 in most cases). The challenge for the future will include cataloging and confirming the genetic risk factors, and understanding how these risk factors interact with each other and with the known environmental and lifestyle risk factors that increase the propensity to type 2 diabetes.

Functional mapping of disease susceptibility loci using cell biology

In most genome-wide linkage studies, implication of a causative disease gene often requires years of expanding the study to more families and finer mapping of the initially described region. Even after such efforts, unobtainable sample sizes can be required to make statistically meaningful conclusions about a single gene. Here we demonstrate that by adding a layer of functional biology to statistical genetic results, this process can be accelerated. The diabetes susceptibility locus (chromosome 18p11) was systematically dissected by using a cell-based secretion assay and RNA interference, and we identified laminin alpha1 to have a role in pancreatic beta cell secretion. The screen was extended to identify laminin receptor 1 as a functional partner in regards to beta cell function. Our approach can potentially be widely used in the setting of high-throughput cellular screening of other loci to identify candidate genes.

The CIDEA gene V115F polymorphism is associated with obesity in Swedish subjects

The cell death-inducing DFFA (DNA fragmentation factor-alpha)-like effector A (CIDEA) gene is implicated as an important regulator of body weight in mice and humans and is therefore a candidate gene for human obesity. Here, we characterize common CIDEA gene polymorphisms and investigate them for association with obesity in two independent Swedish samples; the first comprised 981 women and the second 582 men. Both samples display a large variation in BMI. The only detected coding polymorphism encodes an exon 4 V115F amino acid substitution, which is associated with BMI in both sexes (P = 0.021 for women, P = 0.023 for men, and P = 0.0015 for joint analysis). These results support a role for CIDEA alleles in human obesity. CIDEA-deficient mice display higher metabolic rate, and the gene cross-talks with tumor necrosis factor-alpha (TNF-alpha) in fat cells. We hypothesize that CIDEA alleles regulate human obesity through impact on basal metabolic rate and adipocyte TNF-alpha signaling.

Two major QTLs and several others relate to factors of metabolic syndrome in the family blood pressure program

Genome-wide variance components linkage analysis was performed on 4 latent factors underlying metabolic syndrome derived from 10 risk factors. The latent factors represent obesity and insulin, blood pressure, lipids and insulin, and central obesity. The metabolic syndrome factor scores were derived in 4 ethnic groups recruited in 3 Networks of the Family Blood Pressure Program: GENOA (blacks, Hispanics, and whites), HyperGEN (blacks and whites), SAPPHIRe (Asians). Heritabilities of metabolic syndrome factors ranged from 66% for obesity and insulin to 11% for blood pressure factor. We observed higher heritabilities for obesity and insulin, and lipids and insulin, whereas those for blood pressure and central obesity were smaller. Linkage analysis detected two major quantitative trait loci. One of them linked to the obesity and insulin factor with a lod score of 3.94 (P=0.00001, marker GATA11A06, D18S53, 41.24 cM) at marker positions linkage (lod 4.71, at 46.84 cM at 1-cM-apart distances linkage), located on chromosome 18p11.21 in GENOA black. The other linked to the blood pressure factor with a lod score of 3.22 (P=0.000059, marker GATA49C09, D17S1290, 82 cM) at marker positions linkage (lod 3.56, at 84.63 cM for 1 cM apart distances linkage) located on chromosome 17q23.1 in Hispanics. These quantitative trait loci, together with 4 additional ones with lod scores >2.5, and 30 additional ones with lod score >1.7, offer hope for dissecting the genetic architecture of metabolic syndrome with beneficial implications for molecular diagnosis, prognosis, and in potential medical intervention.

Genome-wide linkage analyses of type 2 diabetes in Mexican Americans: the San Antonio Family Diabetes/Gallbladder Study

The San Antonio Family Diabetes/Gallbladder Study was initiated to identify susceptibility genes for type 2 diabetes. Evidence was previously reported of linkage to diabetes on 10q with suggestive evidence on 3p and 9p in a genome-wide scan of 440 individuals from 27 pedigrees ascertained through a single diabetic proband. Subsequently, the study was expanded to include 906 individuals from 39 extended Mexican-American pedigrees, two additional examination cycles approximately 5.3 and 7.6 years after baseline, and genotypes for a new set of genome-wide markers. Therefore, we completed a second genome-wide linkage scan. Using information from a participant's most recent exam, the prevalence of diabetes in nonprobands was 21.8%. We performed genome-wide variance components-based genetic analysis on the discrete trait diabetes using a liability model and on the quantitative Martingale residual obtained from modeling age of diabetes diagnosis using Cox proportional hazard models. Controlling for age and age(2), our strongest evidence for linkage to the trait diabetes and the quantitative Martingale residual was on chromosome 3p at marker D3S2406 with multipoint empirical logarithm of odds scores of 1.87 and 3.76, respectively. In summary, we report evidence for linkage to diabetes on chromosome 3p in a region previously identified in at least three independent populations.

Linkage study of the glucagon receptor gene with type 2 diabetes mellitus in Italians

Type 2 diabetes mellitus (T2DM) is a common complex trait disorder. Multiple genome scans have identified different loci in linkage with T2D, including a locus on chromosome 17q24-25. Because the glucagon receptor gene ( GCR ) resides on chromosome 17q25, it might be responsible for the linkage identified in the same region. In a combined French-Sardinian study of GCR , there is an association of Gly 40 Ser mutation with T2DM, confirmed by a UK study but not by others. Our goal was to study this selected region of chromosome 17 in a group of Italian patients with late- and early-onset T2DM by genotyping the microsatellites D17S801, D17S937, and D17S1806 and by performing nonparametric multipoint linkage analysis (Merlin 2000-2002) with allele frequencies calculated from sib-pairs data. We recruited from the center of Italy late-onset sib pairs with T2DM and families with maturity-onset diabetes of the young/early-onset T2DM (N = 503). The linkage analysis at chromosome 17q25 reported no positive lod scores in the total T2D sib pairs, in the late-onset T2D group, and in the early-onset T2D group. Although the study does not show evidence for linkage in this chromosomal region in our Italian cohort, we cannot a priori exclude the possibility of an allelic or genotypic association. Nevertheless, we may conclude that GCR does not play a major role in the pathogenesis of T2DM in Italians.

Genes and Type 2 Diabetes Mellitus

Type 2 diabetes (T2DM) comprises a group of entities with different genetic causes. In most patients, T2DM results from alterations of various genes, each having a partial and additive effect. The inheritance pattern is thus complex, and environmental factors play an important role in favoring or delaying the expression of the disease. The identification of susceptibility genes and genetic variants requires different methodological approaches. Here we address some of the most important strategies and findings on the genomic basis of T2DM, as well as evidence of genetic heterogeneity among populations. The identification of the underlying genetic causes of T2DM and other related traits such as obesity and hypertension will lead to the development of new therapeutic targets likely to impact the way we treat these diseases. Survival and quality of life for T2DM patients is expected to eventually increase, significantly lessening the socioeconomic burden of the disease.

A male-specific quantitative trait locus on 1p21 controlling human stature

BACKGROUND

Many genome-wide scans aimed at complex traits have been statistically underpowered due to small sample size. Combining data from several genome-wide screens with comparable quantitative phenotype data should improve statistical power for the localisation of genomic regions contributing to these traits.

OBJECTIVE

To perform a genome-wide screen for loci affecting adult stature by combined analysis of four previously performed genome-wide scans.

METHODS

We developed a web based computer tool, Cartographer, for combining genetic marker maps which positions genetic markers accurately using the July 2003 release of the human genome sequence and the deCODE genetic map. Using Cartographer, we combined the primary genotype data from four genome-wide scans and performed variance components (VC) linkage analyses for human stature on the pooled dataset of 1417 individuals from 277 families and performed VC analyses for males and females separately.

RESULTS

We found significant linkage to stature on 1p21 (multipoint LOD score 4.25) and suggestive linkages on 9p24 and 18q21 (multipoint LOD scores 2.57 and 2.39, respectively) in males-only analyses. We also found suggestive linkage to 4q35 and 22q13 (multipoint LOD scores 2.18 and 2.85, respectively) when we analysed both females and males and to 13q12 (multipoint LOD score 2.66) in females-only analyses.

CONCLUSIONS

We strengthened the evidence for linkage to previously reported quantitative trait loci (QTL) for stature and also found significant evidence of a novel male-specific QTL on 1p21. Further investigation of several interesting candidate genes in this region will help towards characterisation of this first sex-specific locus affecting human stature.

An autosomal genome-wide scan for loci linked to pre-diabetic phenotypes in nondiabetic Chinese subjects from the Stanford Asia-Pacific Program of Hypertension and Insulin Resistance Family Study

Type 2 diabetes is a complex disease involving both genetic and environmental components. Abnormalities in insulin secretion and insulin action usually precede the development of type 2 diabetes and can serve as good quantitative measures for genetic mapping. We therefore undertook an autosomal genomic search to locate the quantitative trait locus (QTL) linked to these traits in 1,365 nondiabetic Chinese subjects from 411 nuclear families. Residuals of these log-transformed quantitative traits were analyzed in multipoint linkage analysis using a variance-components approach. The most significant QTL for fasting insulin, which coincides with the QTL for homeostasis model assessment of insulin resistance, was located at 37 cM on chromosome 20, with a maximum empirical logarithm of odds (LOD) score of 3.01 (empirical P = 0.00006) when adjusted for age, sex, BMI, antihypertensive medications, recruitment centers, and environmental factors. In the same region, a QTL for fasting glucose was identified at 51 cM, with an empirical LOD score of 2.03 (empirical P = 0.0012). There were other loci with maximum empirical LOD scores >or=1.29 located on chromosomes 1q, 2p, 5q, 7p, 9q, 10p, 14q, 18q, and 19q for different diabetes-related traits. These loci may harbor genes that regulate glucose homeostasis either independently or via interactions of the genes within these regions.

Detecting epistatic interactions contributing to quantitative traits

The restricted partition method (RPM) is a partitioning algorithm for examining multi-locus genotypes as (potentially non-additive) predictors of a quantitative trait. The motivating application was to develop a robust method to examine quantitative phenotypes for epistasis (gene-gene interactions), but the method can be applied without modification to gene-environment interactions. Simulation results indicate that the method provides an efficient way to identify loci contributing epistatically to a quantitative trait, even if the loci have no single locus effects. Statistical significance can be estimated through permutation testing. An example using real data involving the metabolism of a chemotherapy drug is included for illustration. Although the examples in this article involve 2-locus interactions, the RPM is computationally feasible for the analysis of more than two loci or factors.

Genome-wide linkage analysis for severe obesity in french caucasians finds significant susceptibility locus on chromosome 19q

To ascertain whether distinct chromosomal loci existed that were linked to severe obesity, as well as to utilize the increased heritability of this excessive phenotype, we performed a genome-wide scan in severely obese French Caucasians. The 109 selected pedigrees, totaling 447 individuals, required both the proband and a sibling to be severely obese (BMI >or=35 kg/m(2)), and 84.8% of the nuclear families possessed >or=1 morbidly obese sibling (BMI >or=40). Severe and morbid obesity are still relatively rare in France, with rates of 2.5 and 0.6%, respectively. The initial genome scan consisted of 395 evenly spaced microsatellite markers. Six regions were found to have suggestive linkage on 4q, 6cen-q, 17q, and 19q for a BMI >or=35 phenotypic subset, and 5q and 10q for an inclusive BMI >or=27 group. The highest peak on chromosome 19q (logarithm of odds [LOD] = 3.59) was significant by genome scan simulation testing (P = 0.042). These regions then underwent second-stage mapping with an additional set of 42 markers. BMI >or=35 analysis defined regions on 17q23.3-25.1 and 19q13.33-13.43 with an maximum likelihood score LOD of 3.16 and 3.21, respectively. Subsequent pooled data analysis with an additional previous population of 66 BMI >or=35 sib-pairs led to a significant LOD score of 3.8 at the 19q locus (empirical P = 0.023). For more moderate obesity and overweight susceptibility loci, BMI >or=27 analysis confirmed suggestive linkage to chromosome regions 5q14.3-q21.3 (LOD = 2.68) and 10q24.32-26.2 (LOD = 2.47). Plausible positional candidate genes include NR1H2 and TULP2.

Genome-wide scan for type 2 diabetes loci in Hong Kong Chinese and confirmation of a susceptibility locus on chromosome 1q21-q25

We conducted an autosomal genome scan to map loci for type 2 diabetes in a Hong Kong Chinese population. We studied 64 families, segregating type 2 diabetes, of which 57 had at least one member with an age at diagnosis of </=40 years. These families included a total of 126 affected sibpairs and 4 other affected relative pairs. Nonparametric linkage analysis revealed seven regions showing nominal evidence for linkage with type 2 diabetes (logarithm of odds [LOD] >0.59, P(pointwise) < 0.05): chromosome 1 at 173.9 cM (LOD = 3.09), chromosome 3 at 26.3 cM (LOD = 1.27), chromosome 4 at 135.3 cM (LOD = 2.63), chromosome 5 at 139.3 cM (LOD = 0.84), chromosome 6 at 178.9 cM (LOD = 1.91), chromosome 12 at 48.7 cM (LOD = 1.99), and chromosome 18 at 28.1 cM (LOD = 1.00). Simulation studies showed genome-wide significant evidence for linkage of the chromosome 1 region (P(genome-wide) = 0.036). We have confirmed the results of previous studies for the presence of a susceptibility locus on chromosome 1q21-q25 (173.9 cM) and suggest the locations of other loci that may contribute to the development of type 2 diabetes in Hong Kong Chinese.

Evidence from a large U.K. family collection that genes influencing age of onset of type 2 diabetes map to chromosome 12p and to the MODY3/NIDDM2 locus on 12q24

Additional information on genetic susceptibility effects relevant to type 2 diabetes pathogenesis can be extracted from existing genome scans by extending examination to related phenotypes such as age at disease onset. In this study, we report the reanalysis of data from 573 U.K. sibships ascertained for multiplex type 2 diabetes, using age at onset (assessed by the proxy measure of age at diagnosis) as the phenotype of interest. Genome-wide evidence for linkage to age at diagnosis was evaluated using both variance components and Haseman-Elston (HECOM) regression approaches, with extensive simulations to derive empirical significance values. There was broad agreement across analyses with six regions of interest (logarithm of odds [LOD] >/==" BORDER="0">1.18) identified on chromosomes 1qter, 4p15-4q12, 5p15, 12p13-12q13, 12q24, and 14q12-14q21. The strongest empirically "suggestive" evidence for linkage comes from regions on chromosome 12. The first region (12p13-12q13), peaking at D12S310 (variance components LOD [LOD(VC)] = 2.08, empirical pointwise P = 0.0007; HECOM LOD [LOD(HECOM)] = 2.58, P = 0.0010) seems to be novel. The second (12q24) peaking between D12S324 and D12S1659 (LOD(VC) = 1.87, P = 0.0016; LOD(HECOM) = 1.93, P = 0.0027) overlaps a region showing substantial prior evidence for diabetes linkage. These data provide additional evidence that genes mapping to these chromosomal regions are involved in the susceptibility to, and/or development of, type 2 diabetes.

Examination of candidate chromosomal regions for type 2 diabetes reveals a susceptibility locus on human chromosome 8p23.1

In a panel of large Caucasian pedigrees, we genotyped markers in eight chromosomal regions previously reported as supporting linkage with type 2 diabetes. We previously reported significant linkage on chromosome 20q (maximum logarithm of odds score [MLS] = 2.79) in this panel. In the present analysis, candidate regions on 1q, 2q, 3q, 5q, 9q, and 10q yielded little evidence for linkage; a region on 2p (MLS = 1.64, P = 0.01 at position 9.0 cM) gave suggestive evidence of linkage; and a region on 8p (MLS = 3.67, P = 2.8 x 10(-5), at position 7.6 cM) gave significant evidence of linkage. Conditional analyses were performed for both 2p and 8p regions and the region reported on 20q. The MLS for 2p increased from 1.64 to 1.79 (empirical P = 0.142) when conditioned for heterogeneity on 20q. The case was similar for 8p, where the MLS increased from 3.67 to 4.51 (empirical P = 0.023) when conditioned on families without evidence of linkage at 20q. In conclusion, our data support a type 2 diabetes susceptibility locus on chromosome 8p that appears to be independent from other susceptibility loci. Although we were able to replicate linkage in our pedigrees on chromosome 2p, we did not find evidence of linkage for regions on 1q, 2q, 3q, 5q, 9q, or 10q.

Overexpression of pituitary adenylate cyclase-activating polypeptide in islets inhibits hyperinsulinemia and islet hyperplasia in agouti yellow mice

Pituitary adenylate cyclase-activating polypeptide (PACAP) is an intraislet neuropeptide and shares insulinotropic and insulin-sensitizing properties with glucagon-like peptide-1 (GLP-1); however, the pathophysiological significance of PACAP in diabetes remains largely unknown. To assess this, we crossed our recently developed transgenic mice overexpressing PACAP in pancreatic beta-cells (Tg/+), with lethal yellow agouti (KKA(y)) mice (A(y)/+), a genetic model for obesity-diabetes, and examined the metabolic and morphological phenotypes of F(1) animals. Tg/+ mice with the A(y) allele (Tg/+:A(y)/+) developed maturity-onset obesity and diabetes associated with hyperglycemia, hyperlipidemia, and hyperphagia, similar to those of A(y)/+ mice, but hyperinsulinemia was significantly ameliorated in Tg/+:A(y)/+ mice. Although A(y)/+ mice exhibited a marked increase in islet mass resulting from hyperplasia and hypertrophy, this increase was significantly attenuated in Tg/+:A(y)/+ mice. Size frequency distribution analysis revealed that the very large islets comprising one-fourth of islets of A(y)/+ mice were selectively reduced in Tg/+:A(y)/+ mice. Because functional defects have been demonstrated in the large islets of obese animal models, together these findings suggest that PACAP regulates hyperinsulinemia and the abnormal increase in islet mass that occurs during the diabetic process.

The SLC6A14 gene shows evidence of association with obesity

In our previous genome-wide scan of Finnish nuclear families, obesity was linked to chromosome Xq24. Here we analyzed this 15-Mb region by genotyping 9 microsatellite markers and 36 single nucleotide polymorphisms (SNPs) for 11 positional and functional candidate genes in an extended sample of 218 obese Finnish sibling pairs (sibpairs) (BMI > 30 kg/m2). Evidence of linkage emerged mainly from the obese male sibpairs, suggesting a gender-specific effect for the underlying gene. By constructing haplotypes among the obese male sibpairs, we restricted the region from 15 Mb to 4 Mb, between markers DXS8088 and DXS8067. Regional functional candidate genes were tested for association in an initial sample of 117 cases and 182 controls. Significant evidence was observed for association for an SNP in the 3'-untranslated region of the solute carrier family 6 member 14 (SLC6A14) gene (P = 0.0002) and for SNP haplotypes of the SLC6A14 gene (P = 0.0007-0.006). Furthermore, an independent replication study sample of 837 cases and 968 controls from Finland and Sweden also showed significant differences in allele frequencies between obese and non-obese individuals (P = 0.003). The SLC6A14 gene is an interesting novel candidate for obesity because it encodes an amino acid transporter, which potentially regulates tryptophan availability for serotonin synthesis and thus possibly affects appetite control.

An autosome-wide search using longitudinal data for loci linked to type 2 diabetes progression

A genome-wide screen was conducted for type 2 diabetes progression genes using measures of elevated fasting glucose levels as quantitative traits from the offspring enrolled in the Framingham Heart Study. We analyzed young (20–34 years) and old (≥ 35 years) subjects separately, using single-point and multipoint sibpair analysis, because of the possible differential impact of progression on the groups of interest. We observed significant linkage with change in fasting glucose levels on 1q25-32 (p = 5.21 × 10^-8), 3p26.3-21.31 (p = 1 × 10^-11), 8q23.1-24.13 (p = 2.94 × 10^-6), 9p24.1-21.3 (p = 7 × 10^-7), and 18p11.31-q22.1 (p < 10^-11). The evidence for linkage on chromosomes 8 and 18 was consistent for the subset of study participants aged 43 through 55 years.

The inherited basis of diabetes mellitus: implications for the genetic analysis of complex traits

Diabetes encompasses a heterogeneous group of diseases, each with a substantial genetic component. We review the division of diabetes into different subtypes based on clinical phenotype, the fruitful pursuit of genes underlying monogenic forms of the disease, the successes and drawbacks of whole-genome linkage scans in type 1 and type 2 diabetes, and the recent identification of several diabetes genes by large association studies. We use the lessons learned from this extensive body of evidence to illustrate general implications for the genetic analysis of complex traits.

Genome-wide screen in obese pedigrees with type 2 diabetes mellitus from a defined Dutch population

A genome scan was performed in obese type 2 diabetes mellitus pedigrees to identify susceptibility loci involved in obesity-driven type 2 diabetes mellitus. We studied the 20% most obese diabetes pedigrees from a confined Dutch population from around the town of Breda. Previously we, and others, have already shown that a susceptibility locus influencing obesity in diabetes may reside on chromosome 18p11. We now report evidence to also suggest linkage for type 2 diabetes in these obese pedigrees on chromosome regions 11p (genome-wide P-value </= 0.061) and 12q (genome-wide P-value </= 0.029), thereby confirming previous findings from corresponding regions. The linkage found in the Breda Cohort of type 2 diabetes patients is influenced by obesity. This supports the notion that a genetic predisposition to obesity is probably intertwined with a genetic predisposition to type 2 diabetes. Further efforts should address the question of how, on a genetic level, these two factors interact.

A genome-wide search for genes involved in type 2 diabetes in a recently genetically isolated population from the Netherlands

Multiple genes, interacting with the environment, contribute to the susceptibility to type 2 diabetes. We performed a genome-wide search to localize type 2 diabetes susceptibility genes in a recently genetically isolated population in the Netherlands. We identified 79 nuclear families with type 2 diabetes who were related within 13 generations and performed a 770-marker genome-wide scan search for shared founder alleles. Twenty-six markers yielded a logarithm of odds (LOD) score >0.59 (nominal P < 0.05), of which 7 reached LOD scores >1.17 (nominal P < 0.01). The strongest evidence for a type 2 diabetes locus was at marker D18S63 on chromosome 18p (LOD 2.3, P = 0.0006). This region was investigated further using additional markers. For one of these markers (D18S1105), we found a significant association with type 2 diabetes (odds ratio 6.7 [95% CI 1.5-30.7], P = 0.005 for the 97-bp allele, assuming a dominant model), which increased when limiting the analysis to patients with high BMI (12.25 [2.1-71], P = 0.003). A locus on chromosome 18p in patients with high BMI was suggested earlier by Parker et al. Our study is the first to confirm this locus.

Genetic analysis of phenotypes derived from longitudinal data: Presentation Group 1 of Genetic Analysis Workshop 13

The participants of Presentation Group 1 used the GAW13 data to derive new phenotypes, which were then analyzed for linkage and, in one case, for association to the genetic markers. Since the trait measurements ranged over longer time periods, the participants looked at the time dependence of particular traits in addition to the trait itself. The phenotypes analyzed with the Framingham data can be roughly divided into 1) body weight-related traits, which also include a type 2 diabetes progression trait, and 2) traits related to systolic blood pressure. Both trait classes are associated with metabolic syndrome. For traits related to body weight, linkage was consistently identified by at least two participating groups to genetic regions on chromosomes 4, 8, 11, and 18. For systolic blood pressure, or its derivatives, at least two groups obtained linkage for regions on chromosomes 4, 6, 8, 11, 14, 16, and 19. Five of the 13 participating groups focused on the simulated data. Due to the rather sparse grid of microsatellite markers, an association analysis for several traits was not successful. Linkage analysis of hypertension and body mass index using LODs and heterogeneity LODs (HLODs) had low power. For the glucose phenotype, a combination of random coefficient regression models and variance component linkage analysis turned out to be strikingly powerful in the identification of a trait locus simulated on chromosome 5. Haseman-Elston regression methods, applied to the same phenotype, had low power, but the above-mentioned chromosome 5 locus was not included in this analysis.

Localization of a susceptibility gene for type 2 diabetes to chromosome 5q34-q35.2

We report a genomewide linkage study of type 2 diabetes (T2D [MIM 125853]) in the Icelandic population. A list of type 2 diabetics was cross-matched with a computerized genealogical database clustering 763 type 2 diabetics into 227 families. The diabetic patients and their relatives were genotyped with 906 microsatellite markers. A nonparametric multipoint linkage analysis yielded linkage to 5q34-q35.2 (LOD = 2.90, P=1.29 x 10(-4)) in all diabetics. Since obesity, here defined as body mass index (BMI) > or =30 kg/m(2), is a key risk factor for the development of T2D, we studied the data either independently of BMI or by stratifying the patient group as obese (BMI > or =30) or nonobese (BMI <30). A nonparametric multipoint linkage analysis yielded linkage to 5q34-q35.2 (LOD = 3.64, P=2.12 x (10)-5) in the nonobese diabetics. No linkage was observed in this region for the obese diabetics. Linkage analysis conditioning on maternal transmission to the nonobese diabetics resulted in a LOD score of 3.48 (P=3.12 x 10(-5)) in the same region, whereas conditioning on paternal transmission led to a substantial drop in the LOD score. Finally, we observed potential interactions between the 5q locus and two T2D susceptibility loci, previously mapped in other populations.

Impaired insulin secretion and glucose tolerance in beta cell-selective Ca(v)1.2 Ca2+ channel null mice

Insulin is secreted from pancreatic beta cells in response to an elevation of cytoplasmic Ca(2+) resulting from enhanced Ca(2+) influx through voltage-gated Ca(2+) channels. Mouse beta cells express several types of Ca(2+) channel (L-, R- and possibly P/Q-type). beta cell-selective ablation of the gene encoding the L-type Ca(2+) channel subtype Ca(v)1.2 (betaCa(v)1.2(-/-) mouse) decreased the whole-cell Ca(2+) current by only approximately 45%, but almost abolished first-phase insulin secretion and resulted in systemic glucose intolerance. These effects did not correlate with any major effects on intracellular Ca(2+) handling and glucose-induced electrical activity. However, high-resolution capacitance measurements of exocytosis in single beta cells revealed that the loss of first-phase insulin secretion in the betaCa(v)1.2(-/-) mouse was associated with the disappearance of a rapid component of exocytosis reflecting fusion of secretory granules physically attached to the Ca(v)1.2 channel. Thus, the conduit of Ca(2+) entry determines the ability of the cation to elicit secretion.