Precision stratification of prognostic risk factors associated with outcomes in gestational diabetes mellitus: a systematic review

BACKGROUND

The objective of this systematic review is to identify prognostic factors among women and their offspring affected by gestational diabetes mellitus (GDM), focusing on endpoints of cardiovascular disease (CVD) and type 2 diabetes (T2D) for women, and cardiometabolic profile for offspring.

METHODS

This review included studies published in English language from January 1st, 1990, through September 30th, 2021, that focused on the above outcomes of interest with respect to sociodemographic factors, lifestyle and behavioral characteristics, traditional clinical traits, and 'omics biomarkers in the mothers and offspring during the perinatal/postpartum periods and across the lifecourse. Studies that did not report associations of prognostic factors with outcomes of interest among GDM-exposed women or children were excluded.

RESULTS

Here, we identified 109 publications comprising 98 observational studies and 11 randomized-controlled trials. Findings indicate that GDM severity, maternal obesity, race/ethnicity, and unhealthy diet and physical activity levels predict T2D and CVD in women, and greater cardiometabolic risk in offspring. However, using the Diabetes Canada 2018 Clinical Practice Guidelines for studies, the level of evidence was low due to potential for confounding, reverse causation, and selection biases.

CONCLUSIONS

GDM pregnancies with greater severity, as well as those accompanied by maternal obesity, unhealthy diet, and low physical activity, as well as cases that occur among women who identify as racial/ethnic minorities are associated with worse cardiometabolic prognosis in mothers and offspring. However, given the low quality of evidence, prospective studies with detailed covariate data collection and high fidelity of follow-up are warranted.

Bringing precision medicine to the management of pregnancy in women with glucokinase-MODY: a study of diagnostic accuracy and feasibility of non-invasive prenatal testing

AIMS/HYPOTHESIS

In pregnancies where the mother has glucokinase-MODY (GCK-MODY), fetal growth is determined by fetal genotype. When the fetus inherits a maternal pathogenic GCK variant, normal fetal growth is anticipated, and insulin treatment of maternal hyperglycaemia is not recommended. At present, fetal genotype is estimated from measurement of fetal abdominal circumference on ultrasound. Non-invasive prenatal testing of fetal GCK genotype (NIPT-GCK) using cell-free DNA in maternal blood has recently been developed. We aimed to compare the diagnostic accuracy of NIPT-GCK with that of ultrasound, and determine the feasibility of using NIPT-GCK to guide pregnancy management.

METHODS

We studied an international cohort of pregnant women with hyperglycaemia due to GCK-MODY. We compared the diagnostic accuracy of NIPT-GCK with that of measurement of fetal abdominal circumference at 28 weeks' gestation (n=38) using a directly genotyped offspring sample as the reference standard. In a feasibility study, we assessed the time to result given to clinicians in 43 consecutive pregnancies affected by GCK-MODY between July 2019 and September 2021.

RESULTS

In terms of diagnostic accuracy, NIPT-GCK was more sensitive and specific than ultrasound in predicting fetal genotype (sensitivity 100% and specificity 96% for NIPT-GCK vs sensitivity 53% and specificity 61% for fetal abdominal circumference 75th percentile). In terms of feasibility, a valid NIPT-GCK fetal genotype (≥95% probability) was reported in all 38 pregnancies with an amenable variant and repeated samples when needed. The median time to report was 5 weeks (IQR 3-8 weeks). For the 25 samples received before 20 weeks' gestation, results were reported at a median gestational age of 20 weeks (IQR 18-24), with 23/25 (92%) reported before 28 weeks.

CONCLUSIONS/INTERPRETATION

Non-invasive prenatal testing of fetal genotype in GCK-MODY pregnancies is highly accurate and is capable of providing a result before the last trimester for most patients. This means that non-invasive prenatal testing of fetal genotype is the optimal approach to management of GCK-MODY pregnancies.

Predictors and risk factors of short-term and long-term outcomes among women with gestational diabetes mellitus (GDM) and their offspring: Moving toward precision prognosis?

As part of the American Diabetes Association Precision Medicine in Diabetes Initiative (PMDI) - a partnership with the European Association for the Study of Diabetes (EASD) - this systematic review is part of a comprehensive evidence evaluation in support of the 2 ^nd International Consensus Report on Precision Diabetes Medicine. Here, we sought to synthesize evidence from empirical research papers published through September 1 ^st , 2021 to evaluate and identify prognostic conditions, risk factors, and biomarkers among women and children affected by gestational diabetes mellitus (GDM), focusing on clinical endpoints of cardiovascular disease (CVD) and type 2 diabetes (T2D) among women with a history of GDM; and adiposity and cardiometabolic profile among offspring exposed to GDM in utero. We identified a total of 107 observational studies and 12 randomized controlled trials testing the effect of pharmaceutical and/or lifestyle interventions. Broadly, current literature indicates that greater GDM severity, higher maternal body mass index, belonging to racial/ethnic minority group; and unhealthy lifestyle behaviors would predict a woman's risk of incident T2D and CVD, and an unfavorable cardiometabolic profile among offspring. However, the level of evidence is low (Level 4 according to the Diabetes Canada 2018 Clinical Practice Guidelines for diabetes prognosis) largely because most studies leveraged retrospective data from large registries that are vulnerable to residual confounding and reverse causation bias; and prospective cohort studies that may suffer selection and attrition bias. Moreover, for the offspring outcomes, we identified a relatively small body of literature on prognostic factors indicative of future adiposity and cardiometabolic risk. Future high-quality prospective cohort studies in diverse populations with granular data collection on prognostic factors, clinical and subclinical outcomes, high fidelity of follow-up, and appropriate analytical approaches to deal with structural biases are warranted.

Identification of GCK-maturity-onset diabetes of the young in cases of neonatal hyperglycemia: A case series and review of clinical features

Heterozygous mutations in GCK result in a persistent, mildly raised glucose from birth, but it is usually diagnosed in adulthood as maturity-onset diabetes of the young (MODY), where hyperglycemia is often an incidental finding. The hyperglycemia of GCK-MODY is benign and does not require treatment, but is important to be aware of, particularly in females where it has implications for managing pregnancy. We present three cases of neonatal hyperglycemia resulting from a heterozygous mutation in GCK, illustrating its clinical presentation and evolution in early life. In summary, as with adults, neonatal hyperglycemia is an incidental finding, does not require treatment and has no adverse consequences for health. Neonates and their parents should be referred for genetic testing to confirm the diagnosis, avoid a label of diabetes and enable pregnancy counseling for females found to be affected.

Two decades since the fetal insulin hypothesis: what have we learned from genetics?

In 1998 the fetal insulin hypothesis proposed that lower birthweight and adult-onset type 2 diabetes are two phenotypes of the same genotype. Since then, advances in research investigating the role of genetics affecting insulin secretion and action have furthered knowledge of fetal insulin-mediated growth and the biology of type 2 diabetes. In this review, we discuss the historical research context from which the fetal insulin hypothesis originated and consider the position of the hypothesis in light of recent evidence. In summary, there is now ample evidence to support the idea that variants of certain genes which result in impaired pancreatic beta cell function and reduced insulin secretion contribute to both lower birthweight and higher type 2 diabetes risk in later life when inherited by the fetus. There is also evidence to support genetic links between type 2 diabetes secondary to reduced insulin action and lower birthweight but this applies only to loci implicated in body fat distribution and not those influencing insulin resistance via obesity or lipid metabolism by the liver. Finally, we also consider how advances in genetics are being used to explore alternative hypotheses, namely the role of the maternal intrauterine environment, in the relationship between lower birthweight and adult cardiometabolic disease.

All thresholds of maternal hyperglycaemia from the WHO 2013 criteria for gestational diabetes identify women with a higher genetic risk for type 2 diabetes

Background: Using genetic scores for fasting plasma glucose (FPG GS) and type 2 diabetes (T2D GS), we investigated whether the fasting, 1-hour and 2-hour glucose thresholds from the WHO 2013 criteria for gestational diabetes (GDM) have different implications for genetic susceptibility to raised fasting glucose and type 2 diabetes in women from the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) and Atlantic Diabetes in Pregnancy (DIP) studies. Methods: Cases were divided into three subgroups: (i) FPG ≥5.1 mmol/L only, n=222; (ii) 1-hour glucose post 75 g oral glucose load ≥10 mmol/L only, n=154 (iii) 2-hour glucose ≥8.5 mmol/L only, n=73; and (iv) both FPG ≥5.1 mmol/L and either of a 1-hour glucose ≥10 mmol/L or 2-hour glucose ≥8.5 mmol/L, n=172. We compared the FPG and T2D GS of these groups with controls (n=3,091) in HAPO and DIP separately. Results: In HAPO and DIP, the mean FPG GS in women with a FPG ≥5.1 mmol/L, either on its own or with 1-hour glucose ≥10 mmol/L or 2-hour glucose ≥8.5 mmol/L, was higher than controls (all P <0.01). Mean T2D GS in women with a raised FPG alone or with either a raised 1-hour or 2-hour glucose was higher than controls (all P <0.05). GDM defined by 1-hour or 2-hour hyperglycaemia only was also associated with a higher T2D GS than controls (all P <0.05). Conclusions: The different diagnostic categories that are part of the WHO 2013 criteria for GDM identify women with a genetic predisposition to type 2 diabetes as well as a risk for adverse pregnancy outcomes.

All thresholds of maternal hyperglycaemia from the WHO 2013 criteria for gestational diabetes identify women with a higher genetic risk for type 2 diabetes

Background: Using genetic scores for fasting plasma glucose (FPG GS) and type 2 diabetes (T2D GS), we investigated whether the fasting, 1-hour and 2-hour glucose thresholds from the WHO 2013 criteria for gestational diabetes (GDM) have different implications for genetic susceptibility to raised fasting glucose and type 2 diabetes in women from the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) and Atlantic Diabetes in Pregnancy (DIP) studies. Methods: Cases were divided into three subgroups: (i) FPG ≥5.1 mmol/L only, n=222; (ii) 1-hour glucose post 75 g oral glucose load ≥10 mmol/L only, n=154 (iii) 2-hour glucose ≥8.5 mmol/L only, n=73; and (iv) both FPG ≥5.1 mmol/L and either of a 1-hour glucose ≥10 mmol/L or 2-hour glucose ≥8.5 mmol/L, n=172. We compared the FPG and T2D GS of these groups with controls (n=3,091) in HAPO and DIP separately. Results: In HAPO and DIP, the mean FPG GS in women with a FPG ≥5.1 mmol/L, either on its own or with 1-hour glucose ≥10 mmol/L or 2-hour glucose ≥8.5 mmol/L, was higher than controls (all P <0.01). Mean T2D GS in women with a raised FPG alone or with either a raised 1-hour or 2-hour glucose was higher than controls (all P <0.05). GDM defined by 1-hour or 2-hour hyperglycaemia only was also associated with a higher T2D GS than controls (all P <0.05). Conclusions: The different diagnostic categories that are part of the WHO 2013 criteria for GDM identify women with a genetic predisposition to type 2 diabetes as well as a risk for adverse pregnancy outcomes.

All thresholds of maternal hyperglycaemia from the WHO 2013 criteria for gestational diabetes identify women with a higher genetic risk for type 2 diabetes

Background: Using genetic scores for fasting plasma glucose (FPG GS) and type 2 diabetes (T2D GS), we investigated whether the fasting, 1-hour and 2-hour glucose thresholds from the WHO 2013 criteria for gestational diabetes (GDM) have different implications for genetic susceptibility to raised fasting glucose and type 2 diabetes in women from the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) and Atlantic Diabetes in Pregnancy (DIP) studies. Methods: Cases were divided into three subgroups: (i) FPG ≥5.1 mmol/L only, n=222; (ii) 1-hour glucose post 75 g oral glucose load ≥10 mmol/L only, n=154 (iii) 2-hour glucose ≥8.5 mmol/L only, n=73; and (iv) both FPG ≥5.1 mmol/L and either of a 1-hour glucose ≥10 mmol/L or 2-hour glucose ≥8.5 mmol/L, n=172. We compared the FPG and T2D GS of these groups with controls (n=3,091) in HAPO and DIP separately. Results: In HAPO and DIP, the mean FPG GS in women with a FPG ≥5.1 mmol/L, either on its own or with 1-hour glucose ≥10 mmol/L or 2-hour glucose ≥8.5 mmol/L, was higher than controls (all P <0.01). Mean T2D GS in women with a raised FPG alone or with either a raised 1-hour or 2-hour glucose was higher than controls (all P <0.05). GDM defined by 1-hour or 2-hour hyperglycaemia only was also associated with a higher T2D GS than controls (all P <0.05). Conclusions: The different diagnostic categories that are part of the WHO 2013 criteria for GDM identify women with a genetic predisposition to type 2 diabetes as well as a risk for adverse pregnancy outcomes.

A Lower Maternal Cortisol-to-Cortisone Ratio Precedes Clinical Diagnosis of Preterm and Term Preeclampsia by Many Weeks

CONTEXT

Previous studies have shown reduced placental levels of 11-β-hydroxysteroid dehydrogenase type 2 (11βHSD2) in preeclampsia (PE). However, it is unknown if the maternal cortisol-to-cortisone ratio is predictive of placental complications of pregnancy.

OBJECTIVE

To determine the relationship between the maternal serum cortisol-to-cortisone ratio at different stages of pregnancy and the risk of PE or fetal growth restriction (FGR).

DESIGN

Women from the Pregnancy Outcome Prediction Study experiencing PE (n = 194) or FGR (n = 185), plus a random sample of healthy controls (n = 279), were studied. Steroids were measured at ∼12, ∼20, ∼28, and ∼36 weeks of gestational age (wkGA). Separate analyses were performed for outcomes with term or preterm delivery. Associations were modeled using logistic regression.

RESULTS

At 28 wkGA, the cortisol-to-cortisone ratio was negatively associated (OR per 1 SD increase, 95% CI)] with preterm PE (OR 0.33, 95% CI 0.19 to 0.57), term PE (OR 0.61, 95% CI 0.49 to 0.76), and preterm FGR (OR 0.50, 95% CI 0.29 to 0.85). At 36 wkGA, the cortisol-to-cortisone ratio was negatively associated with term PE (OR 0.42, 95% CI 0.32 to 0.55) but not term FGR (OR 1.07, 95% CI 0.87 to 1.31). Associations were not materially affected by adjustment for maternal characteristics.

CONCLUSIONS

A lower maternal serum cortisol-to-cortisone ratio precedes clinical manifestation of PE and preterm FGR by many weeks, despite previous reports of reduced levels of placental 11βHSD2 in these conditions. Our observations implicate enhanced maternal 11βHSD2 activity or reduced 11βHSD type 1 activity in the pathophysiology of PE.

The association between first trimester AFP to PAPP-A ratio and placentally-related adverse pregnancy outcome

INTRODUCTION

Low maternal serum levels of pregnancy-associated plasma protein A (PAPP-A) measured in the first trimester and high levels of alpha fetoprotein (AFP) measured in the second trimester have been associated with adverse pregnancy outcomes reflective of placental insufficiency, and there is a synergistic relationship between the two. We investigated the utility as a screening test of a simple ratio of maternal serum AFP to PAPP-A (AFP:PAPP-A) measured in the first trimester.

METHODS

We studied 4057 nulliparous women with a singleton pregnancy from the Pregnancy Outcome Prediction (POP) study. We studied the predictive ability for adverse outcome of the AFP:PAPP-A ratio measured in the first trimester with and without correction for maternal weight and gestational age at measurement. We compared the AFP:PAPP-A ratio with corrected AFP and PAPP-A on their own and in combination.

RESULTS

An AFP:PAPP-A ratio >10 was associated with placentally-related adverse outcomes, including fetal growth restriction (risk ratio (RR) 3.74, 95% confidence interval (CI) 2.30-6.09), severe preeclampsia (RR 2.12, 95% CI 1.39-3.25) and stillbirth (RR 5.05, 95% CI 1.48-17.18). The ratio performed favorably in predicting adverse pregnancy outcomes when compared with corrected measurements of either AFP or PAPP-A, and was equivalent to a model combining the two. Its predictive ability was not affected by correction for maternal weight or gestational age at measurement.

DISCUSSION

An elevated maternal AFP:PAPP-A ratio in the first trimester is associated with placentally-related adverse outcomes in a cohort of unselected nulliparous women.

Fetal Genotype and Maternal Glucose Have Independent and Additive Effects on Birth Weight

Maternal glycemia is a key determinant of birth weight, but recent large-scale genome-wide association studies demonstrated an important contribution of fetal genetics. It is not known whether fetal genotype modifies the impact of maternal glycemia or whether it acts through insulin-mediated growth. We tested the effects of maternal fasting plasma glucose (FPG) and a fetal genetic score for birth weight on birth weight and fetal insulin in 2,051 European mother-child pairs from the Exeter Family Study of Childhood Health (EFSOCH) and the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study. The fetal genetic score influenced birth weight independently of maternal FPG and impacted growth at all levels of maternal glycemia. For mothers with FPG in the top tertile, the frequency of large for gestational age (birth weight ≥90th centile) was 31.1% for offspring with the highest tertile genetic score and only 14.0% for those with the lowest tertile genetic score. Unlike maternal glucose, the fetal genetic score was not associated with cord insulin or C-peptide. Similar results were seen for HAPO participants of non-European ancestry (n = 2,842 pairs). This work demonstrates that for any level of maternal FPG, fetal genetics has a major impact on fetal growth and acts predominantly through independent mechanisms.

Abdominal Aortic Aneurysm Genetic Associations: Mostly False? A Systematic Review and Meta-analysis

OBJECTIVE/BACKGROUND

Many associations between abdominal aortic aneurysm (AAA) and genetic polymorphisms have been reported. It is unclear which are genuine and which may be caused by type 1 errors, biases, and flexible study design. The objectives of the study were to identify associations supported by current evidence and to investigate the effect of study design on reporting associations.

METHODS

Data sources were MEDLINE, Embase, and Web of Science. Reports were dual-reviewed for relevance and inclusion against predefined criteria (studies of genetic polymorphisms and AAA risk). Study characteristics and data were extracted using an agreed tool and reports assessed for quality. Heterogeneity was assessed using I(2) and fixed- and random-effects meta-analyses were conducted for variants that were reported at least twice, if any had reported an association. Strength of evidence was assessed using a standard guideline.

RESULTS

Searches identified 467 unique articles, of which 97 were included. Of 97 studies, 63 reported at least one association. Of 92 studies that conducted multiple tests, only 27% corrected their analyses. In total, 263 genes were investigated, and associations were reported in polymorphisms in 87 genes. Associations in CDKN2BAS, SORT1, LRP1, IL6R, MMP3, AGTR1, ACE, and APOA1 were supported by meta-analyses.

CONCLUSION

Uncorrected multiple testing and flexible study design (particularly testing many inheritance models and subgroups, and failure to check for Hardy-Weinberg equilibrium) contributed to apparently false associations being reported. Heterogeneity, possibly due to the case mix, geographical, temporal, and environmental variation between different studies, was evident. Polymorphisms in nine genes had strong or moderate support on the basis of the literature at this time. Suggestions are made for improving AAA genetics study design and conduct.

Revelation of intertwining organic and inorganic fractal structures in polymer coatings

X-ray microtomography and serial block face scanning electron microscopy are used to reveal independent clusters of inorganic particles embedded within a polymer. These clusters are interpenetrating, of varying size, and have fractal dimensions that strongly influence transport and structure-property relations. This interpretation forms a baseline for designing hybrid materials for applications in self-healing, drug delivery, and membranes.

Genetic susceptibility to invasive meningococcal disease: MBL2 structural polymorphisms revisited in a large case-control study and a systematic review

Invasive infection caused by Neisseria meningitidis is a worldwide public health problem. Previous reports have indicated that carriage of common 'defective' structural polymorphisms of the host mannose-binding lectin gene (MBL2) greatly increases an individual's risk of developing the disease. We report the largest case-control study so far to investigate the effect of these polymorphisms in meningococcal disease (296 PCR-positive cases and 5196 population controls, all of European ancestry) and demonstrate that no change in risk is associated with the polymorphisms overall or in any age-defined subgroup. This finding contrasts with two smaller studies that reported an increase in risk. A systematic review of all studies of MBL2 polymorphisms in people of European ancestry published since 1999, including 24,693 individuals, revealed a population frequency of the combined 'defective'MBL2 allele of 0.230 (95% confidence limits: 0.226-0.234). The past reported associations of increased risk of meningococcal disease were because of low 'defective' allele frequencies in their study control populations (0.13 and 0.04) that indicate systematic problems with the studies. The data from our study and all other available evidence indicate that MBL2 structural polymorphisms do not predispose children or adults to invasive meningococcal disease.

Coding polymorphisms in the genes of the alternative complement pathway and abdominal aortic aneurysm

Variants in the genes of the alternative complement pathway are associated with risk of numerous inflammatory diseases. Abdominal aortic aneurysm is associated with inflammation and is a common cause of illness and death among European populations. This study tested 49 single nucleotide polymorphisms, including common putatively functional polymorphisms, in the genes of the alternative complement cascade (CFH, CFB, CFD, CFI, properdin, CR1, CR1L, CR2, CD46, vitronectin, C3, C5, C6, C7, C8A, C8B, C8G and C9). The study group were 434 cases with infra-renal aortic diameter ≥30 mm and 378 disease-free controls from two UK centres, all with self-reported European ancestry. There was no evidence for significant association with presence or size of aneurysm following correction for multiple testing. This study suggests that variation in the genes of the alternative pathway is not an important cause of abdominal aortic aneurysm development.

Mutation analysis in Irish families with glomuvenous malformations

BACKGROUND

Glomuvenous malformations (GVMs) are rare bluish lesions that can affect the skin and mucosal surfaces. They represent defects in vasculogenesis. Lesions can occur sporadically or in an autosomal dominant mode of inheritance. Recent studies have shown that mutations in the glomulin gene (GLMN) on chromosome 1p21-22 are responsible for familial GVMs.

OBJECTIVES

To search for mutations in GLMN in Irish families with GVMs.

METHODS

We identified four Irish families with GVMs and confirmed linkage to chromosome 1p21-22 in these cases. We sequenced the glomulin gene in all affected and unaffected members of the families. Results Linkage analysis showed that affected individuals from the families shared a common haplotype. Mutation analysis revealed a delAAGAA mutation in exon 3 of the glomulin gene in all four families with GVMs.

CONCLUSIONS

We confirm that mutations in the glomulin gene are responsible for GVMs and suggest a founder Irish mutation in the glomulin gene in four Irish families.

Association study of detoxification genes in age related macular degeneration

BACKGROUND/AIMS

Age related macular degeneration (AMD) is a complex disorder leading to loss of central vision, and identification of risk factors associated with susceptibility to AMD has been a key objective for ophthalmic genetics research for almost a decade. This association study has examined genetic polymorphisms in 12 candidate genes as possible risk factors for predisposition to the development of the exudative variant of AMD in a Northern Irish population. The choice of genes was based on their function in the breakdown of industrial pollutants, cigarette smoke, defence against oxidative stress, or involvement in the general ageing process.

METHODS

Up to five single nucleotide polymorphisms (SNPs) were typed for CYP1A1, CYP1A2, CYP2E1, CYP2D6, EPHX1, MnSOD, AhR, NAT2, CAT, GPX1, PON1, and ADPRT1 by multiplex snapshot single base primer extension method. Genes showing high linkage disequilibrium (LD) between SNPs were analysed by haplotype analysis. Genes showing low LD were assessed using individual SNPs based on genotypes.

RESULTS

After correction for number of genes/SNPs tested, no significant association with AMD was found although several genes merit further investigation. This study suggests that a coding SNP in EPHX1 (Y113H) may be important in AMD and supports a previous observation of an association with exudative AMD. In addition, haplotype analysis highlighted ADPRT1, CYP2D6, and AhR as worthy of further study.

CONCLUSION

This study has identified a number of genes requiring further investigation including EPHX1, ADPRT1, CYP2D6, and AhR.

A physical and expression map of the D17S1810-D17S1353 region spanning the central areolar choroidal dystrophy locus

Central areolar choroidal dystrophy (CACD) causes bilateral irreversible central visual loss in the 5th to 7th decades. The authors previously described a large pedigree with the disorder, which showed linkage to chromosome 17p13.2-->p13.1 between microsatellite markers D17S1353 and D17S1810. 17p13 is very rich in genes that cause retinal diseases. We have now constructed a detailed and ordered physical map of the critical CACD region which spans up to 2.4 Mb. The new transcript map contains thirteen genes and seven expressed sequence tags (ESTs) that are eye-expressed, and therefore are positional candidates. Several of these have been screened, but no disease-causing mutations were found in CACD patients.

Spectrum of dominant mutations in the desmosomal cadherin desmoglein 1, causing the skin disease striate palmoplantar keratoderma

The adhesive proteins of the desmosome type of cell junction consist of two types of cadherin found exclusively in that structure, the desmogleins and desmocollins, coded by two closely linked loci on human chromosome 18q12.1. Recently we have identified a mutation in the DSG1 gene coding for desmoglein 1 as the cause of the autosomal dominant skin disease striate palmoplantar keratoderma (SPPK) in which affected individuals have marked hyperkeratotic bands on the palms and soles. In the present study we present the complete exon-intron structure of the DSG1 gene, which occupies approximately 43 kb, and intron primers sufficient to amplify all the exons. Using these we have analysed the mutational changes in this gene in five further cases of SPPK. All were heterozygotic mutations in the extracellular domain leading to a truncated protein, due either to an addition or deletion of a single base, or a base change resulting in a stop codon. Three mutations were in exon 9 and one in exon 11, both of which code for part of the third and fourth extracellular domains, and one was in exon 2 coding for part of the prosequence of this processed protein. This latter mutation thus results in the mutant allele synthesising only 25 amino acid residues of the prosequence of the protein so that this is effectively a null mutation implying that dominance in the case of this mutation was caused by haploinsufficiency. The most severe consequences of SPPK mutations are in regions of the body where pressure and abrasion are greatest and where desmosome function is most necessary. SPPK therefore provides a very sensitive measure of desmosomal function.

Molecular confirmation of the unique phenotype of epidermolysis bullosa simplex with mottled pigmentation

BACKGROUND

A distinctive subtype of epidermolysis bullosa simplex, with the additional feature of mottled pigmentation (EBS-MP), was initially characterized in a Swedish family in 1979, and seven further families have been reported. Features of EBS-MP that are observed in most affected patients include acral blistering early in childhood, mottled pigmentation distributed in a number of sites, focal punctate hyperkeratoses of the palms and soles, and dystrophic, thickened nails. The genetic basis of EBS-MP has been ascribed in five unrelated families to a heterozygous point mutation, P25L, in the non-helical V1 domain of K5.

OBJECTIVES

We report a clinical, ultrastructural and molecular study of two of the earliest families to be clinically characterized as EBS-MP.

METHODS

The P25L mutation was identified in all affected members of each of these families, bringing the total number of EBS-MP families with this mutation to seven.

RESULTS

This unusual recurrent mutation may uniquely cause EBS-MP.

CONCLUSIONS

While the exact molecular mechanisms by which this mutation causes epidermolysis, palmoplantar keratoderma and pigmentation remain elusive, we suggest possible molecular mechanisms through which the P25L substitution could cause this unusual phenotype.

Mutations in TNFRSF11A, affecting the signal peptide of RANK, cause familial expansile osteolysis

Familial expansile osteolysis (FEO, MIM 174810) is a rare, autosomal dominant bone disorder characterized by focal areas of increased bone remodelling. The osteolytic lesions, which develop usually in the long bones during early adulthood, show increased osteoblast and osteoclast activity. Our previous linkage studies mapped the gene responsible for FEO to an interval of less than 5 cM between D18S64 and D18S51 on chromosome 18q21.2-21.3 in a large Northern Irish family. The gene encoding receptor activator of nuclear factor-kappa B (RANK; ref. 5), TNFRSF11A, maps to this region. RANK is essential in osteoclast formation. We identified two heterozygous insertion mutations in exon 1 of TNFRSF11A in affected members of four families with FEO or familial Paget disease of bone (PDB). One was a duplication of 18 bases and the other a duplication of 27 bases, both of which affected the signal peptide region of the RANK molecule. Expression of recombinant forms of the mutant RANK proteins revealed perturbations in expression levels and lack of normal cleavage of the signal peptide. Both mutations caused an increase in RANK-mediated nuclear factor-kappaB (NF-kappaB) signalling in vitro, consistent with the presence of an activating mutation.

A case-control study of candidate vasoactive mediator genes in primary Raynaud's phenomenon

OBJECTIVES

To elucidate possible genetic factors involved in the pathogenesis of primary Raynaud's phenomenon (RP) and to determine the demographic features.

METHODS

The allele frequencies of known polymorphisms in four vasoactive candidate genes, eNOS, BKRG, ET-1 and the ETA receptor genes, were compared in a phenotypically homogeneous group of patients with primary RP and a normal control population.

RESULTS

In patients with primary RP, there was a higher reporting of both a family history of RP than in controls (45.3% vs 3.1%; P<0.0001) and a personal history of migraine (32.6% vs 7.2%; P<0.0001). No significant differences in allele frequencies of the candidate genes were found.

CONCLUSIONS

These findings support the concept that genetic susceptibility exists in primary RP. The high prevalence of migraine suggests that primary RP is part of a more widespread disorder of vascular tone. These findings do not suggest that common molecular variants of these candidate genes are involved in primary RP.

Genotyping and functional analysis of a polymorphic (CCTTT)(n) repeat of NOS2A in diabetic retinopathy

Accumulating evidence shows that the severity and rapidity of onset of diabetic retinopathy are influenced by genetic factors. Expression of the nitric oxide synthases is altered in the retinal vasculature in the early stages of diabetic retinopathy. We analyzed the allele distribution of a polymorphic pentanucleotide repeat within the 5' upstream promoter region of the NOS2A gene in samples of diabetic patients. In diabetic patients from Northern Ireland, the 14-repeat allele of the NOS2A marker was significantly associated with the absence of diabetic retinopathy. Carriers of this repeat had 0.21-fold the relative risk of developing diabetic retinopathy than noncarriers of this allele. They also had significantly fewer renal and cardiovascular complications. The ability of differing numbers of (CCTTT)(n) pentanucleotide repeats to induce transcription of the NOS2A gene was analyzed using a luciferase reporter gene assay in transfected colonic carcinoma cells. Interleukin 1beta (IL-1beta) induction was most effective in constructs carrying the 14-repeat allele. When cells were incubated in 25 mM glucose to mimic the diabetic state, IL-1beta induction was inhibited in all cases, but to a significantly lesser extent with the 14-repeat allele. These unique properties of the 14-repeat allele may confer selective advantages in diabetic individuals, which may delay or prevent microvascular complications of diabetes.

Improved prognosis for congenital nephrotic syndrome of the Finnish type in Irish families

Congenital nephrotic syndrome of the Finnish type is a rare autosomal recessive disease with a high infant mortality without aggressive treatment. The biochemical basis of the disease is not understood fully but the disease locus has been mapped recently to chromosome 19q12-q13.1 in Finnish families. This paper describes the clinical features and outcome of 20 patients in Ireland with congenital nephrotic syndrome of the Finnish type who have presented since 1980. Before 1987, all infants died by the age of 3 years. After the introduction of daily intravenous albumin infusion, nutritional support, elective bilateral nephrectomy, and renal transplantation, mortality in the past decade has fallen to 30%, with no deaths in the past five years. Genetic linkage analysis was performed in six families in whom DNA was available and the locus responsible was mapped to the same region on chromosome 19 as in Finnish families, suggesting that Irish families share the same disease locus.

Dinucleotide repeat polymorphisms in EDN1 and NOS3 are not associated with severe diabetic retinopathy in type 1 or type 2 diabetes

PURPOSE

Endothelin-1, and constitutive endothelial nitric oxide synthase, have been implicated in the pathogenesis of diabetic retinopathy. We therefore screened polymorphisms within the genes encoding these two vasoactive agents in a sample of individuals with 15 years of diabetes and no retinopathy (ETDRS level 10 or better) and those with severe retinopathy (ETDRS level 50 or worse).

METHODS

PCR primers for highly polymorphic sites within the EDN1 and NOS3 genes were used to genotype individuals with type 1 or type 2 diabetes with severe or no retinopathy. Allele frequencies were compared between groups using chi-squared analysis and adjusting for multiple comparisons.

RESULTS

No significant differences were observed in allele frequencies for these two markers between the patients who had retinopathy and the patients who did not.

CONCLUSION

Polymorphic variability in the EDN1 and NOS3 genes does not appear to have a major impact on determining susceptibility or resistance to diabetic retinopathy.