Transancestral fine-mapping of four type 2 diabetes susceptibility loci highlights potential causal regulatory mechanisms.

To gain insight into potential regulatory mechanisms through which the effects of variants at four established type 2 diabetes (T2D) susceptibility loci (CDKAL1, CDKN2A-B, IGF2BP2 and KCNQ1) are mediated, we undertook transancestral fine-mapping in 22 086 cases and 42 539 controls of East Asian, European, South Asian, African American and Mexican American descent. Through high-density imputation and conditional analyses, we identified seven distinct association signals at these four loci, each with allelic effects on T2D susceptibility that were homogenous across ancestry groups. By leveraging differences in the structure of linkage disequilibrium between diverse populations, and increased sample size, we localised the variants most likely to drive each distinct association signal. We demonstrated that integration of these genetic fine-mapping data with genomic annotation can highlight potential causal regulatory elements in T2D-relevant tissues. These analyses provide insight into the mechanisms through which T2D association signals are mediated, and suggest future routes to understanding the biology of specific disease susceptibility loci.

Discovery and Fine-Mapping of Glycaemic and Obesity-Related Trait Loci Using High-Density Imputation.

Reference panels from the 1000 Genomes (1000G) Project Consortium provide near complete coverage of common and low-frequency genetic variation with minor allele frequency ≥0.5% across European ancestry populations. Within the European Network for Genetic and Genomic Epidemiology (ENGAGE) Consortium, we have undertaken the first large-scale meta-analysis of genome-wide association studies (GWAS), supplemented by 1000G imputation, for four quantitative glycaemic and obesity-related traits, in up to 87,048 individuals of European ancestry. We identified two loci for body mass index (BMI) at genome-wide significance, and two for fasting glucose (FG), none of which has been previously reported in larger meta-analysis efforts to combine GWAS of European ancestry. Through conditional analysis, we also detected multiple distinct signals of association mapping to established loci for waist-hip ratio adjusted for BMI (RSPO3) and FG (GCK and G6PC2). The index variant for one association signal at the G6PC2 locus is a low-frequency coding allele, H177Y, which has recently been demonstrated to have a functional role in glucose regulation. Fine-mapping analyses revealed that the non-coding variants most likely to drive association signals at established and novel loci were enriched for overlap with enhancer elements, which for FG mapped to promoter and transcription factor binding sites in pancreatic islets, in particular. Our study demonstrates that 1000G imputation and genetic fine-mapping of common and low-frequency variant association signals at GWAS loci, integrated with genomic annotation in relevant tissues, can provide insight into the functional and regulatory mechanisms through which their effects on glycaemic and obesity-related traits are mediated.

A comprehensive investigation of variants in genes encoding adiponectin (ADIPOQ) and its receptors (ADIPOR1/R2), and their association with serum adiponectin, type 2 diabetes, insulin resistance and the metabolic syndrome.

BACKGROUND: Low levels of serum adiponectin have been linked to central obesity, insulin resistance, metabolic syndrome, and type 2 diabetes. Variants in ADIPOQ, the gene encoding adiponectin, have been shown to influence serum adiponectin concentration, and along with variants in the adiponectin receptors (ADIPOR1 and ADIPOR2) have been implicated in metabolic syndrome and type 2 diabetes. This study aimed to comprehensively investigate the association of common variants in ADIPOQ, ADIPOR1 and ADIPOR2 with serum adiponectin and insulin resistance syndromes in a large cohort of European-Australian individuals. METHODS: Sixty-four tagging single nucleotide polymorphisms in ADIPOQ, ADIPOR1 and ADIPOR2 were genotyped in two general population cohorts consisting of 2,355 subjects, and one cohort of 967 subjects with type 2 diabetes. The association of tagSNPs with outcomes were evaluated using linear or logistic modelling. Meta-analysis of the three cohorts was performed by random-effects modelling. RESULTS: Meta-analysis revealed nine genotyped tagSNPs in ADIPOQ significantly associated with serum adiponectin across all cohorts after adjustment for age, gender and BMI, including rs10937273, rs12637534, rs1648707, rs16861209, rs822395, rs17366568, rs3774261, rs6444175 and rs17373414. The results of haplotype-based analyses were also consistent. Overall, the variants in the ADIPOQ gene explained <5% of the variance in serum adiponectin concentration. None of the ADIPOR1/R2 tagSNPs were associated with serum adiponectin. There was no association between any of the genetic variants and insulin resistance or metabolic syndrome. A multi-SNP genotypic risk score for ADIPOQ alleles revealed an association with 3 independent SNPs, rs12637534, rs16861209, rs17366568 and type 2 diabetes after adjusting for adiponectin levels (OR=0.86, 95% CI=(0.75, 0.99), P=0.0134). CONCLUSIONS: Genetic variation in ADIPOQ, but not its receptors, was associated with altered serum adiponectin. However, genetic variation in ADIPOQ and its receptors does not appear to contribute to the risk of insulin resistance or metabolic syndrome but did for type 2 diabetes in a European-Australian population.

Impact of the Reelin signaling cascade (ligands-receptors-adaptor complex) on cognition in schizophrenia.

Our previous neurocognitive studies of schizophrenia outlined two clusters of affected subjects--cognitively spared (CS) and cognitive deficit (CD), the latter's characteristics pointing to developmental origins and impaired synaptic plasticity. Here we investigate the contribution of polymorphisms in major regulators of these processes to susceptibility to schizophrenia and to CD in patients. We examine variation in genes encoding proteins at the gateway of Reelin signaling: ligands RELN and APOE, their common receptors APOER2 and VLDLR, and adaptor DAB1. Association analysis with disease outcome and cognitive performance in the Western Australian Family Study of Schizophrenia (WAFSS) was followed by replication analysis in the Australian Schizophrenia Research Bank (ASRB) and in the Health in Men Study (HIMS) of normal aging males. In the WAFSS sample, we observed significant association of APOE, APOER2, VLDLR, and DAB1 SNPs with disease outcome in the case-control and CD-control datasets, and with pre-morbid intelligence and verbal memory in cases. HIMS replication analysis supported rs439401 (APOE regulatory region), and rs2297660 and rs3737983 (APOER2), with an effect on memory performance in normal aging subjects consistent with the findings in schizophrenia cases. APOER2 gene expression analysis revealed lower transcript levels in lymphoblastoid cells from cognitively impaired schizophrenia patients of the alternatively spliced exon 19, mediating Reelin signaling and synaptic plasticity in the adult brain. ASRB replication analysis produced marginally significant results, possibly reflecting a recruitment strategy biased toward CS patients. The data suggest a contribution of neurodevelopmental/synaptic plasticity genes to cognitive impairment in schizophrenia.

Celestial3D: a novel method for 3D visualization of familial data.

SUMMARY: Traditional two-dimensional (2D) software programs for drawing pedigrees are limited when dealing with extended pedigrees. In successive generations, the number of individuals grows exponentially, leading to an unworkable amount of space required in the horizontal direction for 2D displays. In addition, it is not always possible to place closely related individuals near each other due to the lack of space in 2Ds. To address these issues we have developed three-dimensional (3D) pedigree drawing techniques to enable clearer visualization of extended pedigrees. Currently no other methods are available for displaying extended pedigrees in 3Ds. We have made freely available a software tool--'Celestial3D'--that implements these novel techniques. AVAILABILITY: Freely available to non-commercial users.

Ovarian morphology is a marker of heritable biochemical traits in sisters with polycystic ovaries.

CONTEXT: Polycystic ovary syndrome (PCOS) is a common endocrinopathy of uncertain etiology but with strong evidence for a genetic contribution. OBJECTIVE: The objective of the study was to test the hypothesis that the typical polycystic ovarian morphology is a marker of inherited biochemical features in families of women with PCOS. DESIGN: A study of probands with PCOS and their sisters. PATIENTS: Patients included 125 probands and 214 sisters. All probands had PCOS, defined by symptoms of anovulation and/or hyperandrogenism with polycystic ovaries on ultrasound. Affected sisters were defined by polycystic ovaries, regardless of symptoms, and unaffected sisters defined by normal ovarian morphology. SETTING: This was a clinic-based study. MAIN OUTCOME MEASURES: Clinical, endocrine, and metabolic features in the various groups were compared, and estimates of broad-sense heritability were obtained using the quantitative transmission disequilibrium test. RESULTS: Although affected sisters had fewer symptoms than probands (30% had no symptoms of PCOS), serum testosterone, androstenedione, LH, and fasting insulin and insulin sensitivity were similar in the two groups with polycystic ovaries but significantly different from those in unaffected sisters or controls. We observed moderate to high heritabilities for all traits studied in affected sister pairs, whereas heritabilities calculated from discordant siblings were substantially lower. CONCLUSIONS: These data provide further evidence for a genetic basis of PCOS. The high heritability of biochemical features in probands and affected sisters, despite wide variation in symptoms, shows that not only are these biochemical traits strongly influenced by genetic factors but also, importantly, that polycystic ovarian morphology is an index of inherited traits in families with PCOS.

Association of PARL rs3732581 genetic variant with insulin levels, metabolic syndrome and coronary artery disease.

PARL (presenilin-associated rhomboid-like) is a mitochondrial protein involved in mitochondrial membrane remodelling, and maps to a quantitative trait locus (3q27) associated with metabolic traits. Recently the rs3732581 (Leu262Val) variant was found to be associated with increased levels of plasma insulin, a finding not replicated in a larger cohort. The aim of the current study was to investigate the associations between rs3732581 and levels of plasma insulin, metabolic syndrome (MetS) and its components, and cardiovascular disease. The CUPID population consisted of 556 subjects with angiographically proven CAD and the CUDAS cohort consisted of 1,109 randomly selected individuals from Perth, Western Australia. Samples were genotyped using mutation-specific PCR. No significant associations were observed between rs3732581 and levels of plasma insulin, glucose, BMI or MetS in either population. However, carriers of the minor allele had significantly lower mean intima-media thickness (IMT) [0.69 mm, 95% CI (0.69, 0.70 mm); P = 0.004], compared with major allele homozygotes [mean IMT = 0.71 mm, 95% CI (0.70, 0.72 mm)] in the CUDAS population. Further analysis using a recessive model showed homozygous carriers of the minor allele were predisposed to CAD [OR 1.55, 95% CI (1.11, 2.16); P = 0.01]. Despite the functional evidence for a role of PARL in regulating insulin levels, no association with rs3732581 was found in the current study. Additionally, there were no associations with glucose levels, BMI or MetS. There were significant effects of the variant on mean IMT and risk of CAD. A role for PARL in metabolic conditions cannot be excluded and more comprehensive genetic studies are warranted.

Investigating the association between K198N coding polymorphism in EDN1 and hypertension, lipoprotein levels, the metabolic syndrome and cardiovascular disease.

Endothelin-1 is a potent vasoconstrictor in the body. Previous studies have identified associations between the coding polymorphism K198N and hypertension, systolic blood pressure and HDL levels. We sought to examine the evidence for these associations and, additionally, the association between K198N, insulin resistance, metabolic syndrome and coronary artery disease (CAD). We used generalised linear modelling to test K198N for association with hypertension and systolic blood pressure, lipid levels, insulin resistance scores and metabolic syndrome in a general cross-sectional community sample. Mean carotid intima media thickness and risk of carotid plaque were examined in the general population sample, and Gensini score was examined in a sample of patients with CAD. A case/control sample was used to examine the association of K198N with risk of CAD. There was no significant evidence for association between K198N and hypertension, systolic blood pressure, lipid levels, insulin resistance or metabolic syndrome in either population. The minor allele was marginally associated with increased mean IMT levels (P = 0.02) in the general population sample, although not with CAD in the case/control study or with the severity of disease in patients with CAD. In conclusion, we found no robust evidence for the associations between K198N and hypertension, systolic blood pressure or HDL levels seen in previous studies.

Association of Interleukin-1 gene polymorphisms with central obesity and metabolic syndrome in a coronary heart disease population.

The objective of this study was to determine whether single nucleotide polymorphisms (SNPs) in the Interleukin-1 (IL-1) gene family are associated with central obesity and metabolic syndrome in a coronary heart disease population. The IL-1 alpha C-889T (rs1800587) and IL-1 beta +3954 (rs1143634) SNPs were studied in a Western Australian coronary heart disease (CHD) population (N = 556). Subjects who were TT homozygous at either SNP had larger waist circumference (IL-1 alpha: 1.8 cm greater, P = 0.04; IL-1 beta: 4 cm greater, P = 0.0004) compared with major allele homozygotes. Individuals with two copies of the IL-1 alpha:IL-1 beta T:T haplotype had greater waist circumference (4.7 cm greater, P = 0.0001) compared to other haplotypes. There was a significant interaction between the IL-1 beta SNP and BMI level on waist circumference (P = 0.01). When the cohort was stratified by median BMI, TT carriers for IL-1 beta with above median BMI had greater waist circumference (6.1 cm greater, P = 0.007) compared to baseline carriers, whilst no significant association was seen in the below median group. Similarly, when the cohort was stratified by median fibrinogen level (IL-1 alpha interaction P = 0.01; IL-1 beta interaction P = 0.04), TT carriers for both SNPs in the above median fibrinogen group had greater waist circumference (IL-1 alpha 2.7 cm greater, P = 0.007; IL-1 beta 3.3 cm greater, P = 0.003) compared with major allele homozygotes. This association was not seen in the below median group. Also, we found a trend of increased metabolic syndrome for IL-1 beta TT homozygotes (P = 0.07). In conclusion, our findings suggest that in a CHD population IL-1 gene polymorphisms may be involved in increased central obesity, and the genetic influences are more evident among patients who have a higher level of obesity or inflammatory markers.

Comprehensive analysis of tagging sequence variants in DTNBP1 shows no association with schizophrenia or with its composite neurocognitive endophenotypes.

In a previous study we identified a relatively homogeneous subtype of schizophrenia characterized by pervasive cognitive deficit, which was the exclusive contributor to our findings of linkage to 6p25-p24. The 6p region contains Dysbindin (DTNBP1), considered to be one of the major schizophrenia candidate genes. While multiple studies have reported association between genetic variation in DTNBP1 and schizophrenia, the findings have been inconsistent and controversial, leading to recent calls for systematic re-examination and unambiguous evidence of association. To address this, we have undertaken a comprehensive survey of common genetic variation within DTNBP1 and its association with schizophrenia, using a HapMap-based gene-tagging approach. We genotyped 39 tSNPs in a sample of 336 cases and 172 controls of Anglo-Irish ancestry, with the phenotype defined as clinical schizophrenia, and as composite neurocognitive endophenotypes. Allele and haplotype frequencies, and LD structure in our control sample were similar to those in other European populations. Using multivariate generalized linear modeling, we observed no significant association between any tSNP and any outcome variable. Association with haplotypes was examined across the gene and in the previously associated 5' region. Neither global haplotype tests, nor specific analysis of the "risk" haplotype previously reported in an ethnically related population, the Irish high-density schizophrenia families, showed significant evidence of association with schizophrenia or with the neurocognitive endophenotypes in our sample. The framework and results of this study should facilitate further attempts at re-analysis of DTNBP1, in terms of standardized approaches to both phenotype definition and analysis of genetic variation.

Examining the candidacy of ghrelin as a gene responsible for variation in adult stature in a United Kingdom population with type 2 diabetes.

CONTEXT: Recently, a quantitative trait locus for stature was reported on chromosome 3p26 in patients with type 2 diabetes. OBJECTIVE: Given that ghrelin is a peptide involved in GH release and located on 3p26, we hypothesized that variation within its gene (GHRL) may be responsible for the quantitative trait locus on 3p26. DESIGN: The evidence for linkage around GHRL was refined with the genotyping of an additional four microsatellites (D3S4545, D3S1537, D3S1597, and D3S3611), giving a total of 27 markers, followed by multipoint variance components linkage analysis. Probands from the linkage families were typed for five common single nucleotide polymorphisms (SNPs) within GHRL and tested for association with adult stature using haplotype trend regression. RESULTS: The maximum multipoint evidence for linkage between adult stature and the 27 microsatellites yielded an LOD score of 2.58 (P = 0.0003) between D3S1297 and D3S1304. Five common (frequency of > or =5%) SNPs were typed in the probands [two promoter SNPs (rs27647 and rs26802), two exonic (rs696217 and rs4684677), and one intronic (rs35683)] capturing 80% of the total common variation in GHRL. No association was found between any SNP (or haplotypes thereof) and adult stature. CONCLUSION: Common genetic variation within GHRL is not responsible for variation in adult stature in this population.

Association analysis of 6,736 U.K. subjects provides replication and confirms TCF7L2 as a type 2 diabetes susceptibility gene with a substantial effect on individual risk.

Recent data suggest that common variation in the transcription factor 7-like 2 (TCF7L2) gene is associated with type 2 diabetes. Evaluation of such associations in independent samples provides necessary replication and a robust assessment of effect size. Using four TCF7L2 single nucleotide polymorphisms (SNPs; including the two most associated in the previous study), we conducted a case-control study in 2,158 type 2 diabetic subjects and 2,574 control subjects and a family-based association analysis in 388 parent-offspring trios all from the U.K. All SNPs showed powerful associations with diabetes in the case-control analysis, with strongest effects at rs7903146 (allele-wise relative risk 1.36 [95% CI 1.24-1.48], P = 1.3 x 10(-11)). Data were consistent with a multiplicative model. The family-based analyses provided independent evidence for association at all loci (e.g., rs4506565, 62% transmission, P = 7 x 10(-5)) with no parent-of-origin effects. The frequency of diabetes-associated TCF7L2 genotypes was greater in cases ascertained for positive family history and early onset (rs4606565, P = 0.02); the population-attributable risk, estimated from the least-selected cases, is approximately 16%. The overall evidence for association for these variants (P = 4.4 x 10(-14) combining case-control and family-based analyses for rs4506565) exceeds genome-wide significance criteria and clearly establishes TCF7L2 as a type 2 diabetes susceptibility gene of substantial importance.

Significant linkage of BMI to chromosome 10p in the U.K. population and evaluation of GAD2 as a positional candidate.

Obesity is a major health problem, and many family-based studies have suggested that it has a strong genetic basis. We performed a genome-wide quantitative trait linkage scan for loci influencing BMI in 573 pedigrees from the U.K. We identified genome-wide significant linkage (logarithm of odds = 3.74, between D10S208 and D10S196, genome-wide P=0.0186) on chromosome 10p. The size of our study population and the statistical significance of our findings provide substantial contributions to the body of evidence for a locus on chromosome 10p. We examined eight single nucleotide polymorphisms (SNPs) in GAD2, which maps to this linkage region, tagging the majority of variation in the gene, and observed marginally significant (0.01

High-density haplotype structure and association testing of the insulin-degrading enzyme (IDE) gene with type 2 diabetes in 4,206 people.

The insulin-degrading enzyme is responsible for the intracellular proteolysis of insulin. Its gene IDE is located on chromosome 10, in an area with suggestive linkage to type 2 diabetes and related phenotypes. Due to the impact of genetic variants of this gene in rodents and the function of its protein product, it has been proposed as a candidate gene for type 2 diabetes. Various groups have explored the role of the common genetic variation of IDE on insulin resistance and reported associations of various single nucleotide polymorphisms (SNPs) and haplotypes on both type 2 diabetes and glycemic traits. We sought to characterize the haplotype structure of IDE in detail and replicate the association of common variants with type 2 diabetes, fasting insulin, fasting glucose, and insulin resistance. We assessed linkage disequilibrium, selected single-marker and multimarker tags, and genotyped these markers in several case-control and family-based samples totalling 4,206 Caucasian individuals. We observed no statistically significant evidence of association between single-marker or multimarker tests in IDE and type 2 diabetes. Nominally significant differences in quantitative traits are consistent with statistical noise. We conclude that common genetic variation at IDE is unlikely to confer clinically significant risk of type 2 diabetes in Caucasians.

The value of gene-based selection of tag SNPs in genome-wide association studies.

Genome-wide association scans are rapidly becoming reality, but there is no present consensus regarding genotyping strategies to optimise the discovery of true genetic risk factors. For a given investment in genotyping, should tag SNPs be selected in a gene-centric manner, or instead, should coverage be optimised based on linkage disequilibrium alone? We explored this question using empirical data from the HapMap-ENCODE project, and we found that tags designed specifically to capture common variation in exonic and evolutionarily conserved regions provide good coverage for 15-30% of the total common variation (depending on the population sample studied), and yield genotype savings compared with an anonymous tagging approach that captures all common variation. However, the same number of tags based on linkage disequilibrium alone captures substantially more (30-46%) of the total common variation. Therefore, the best strategy depends crucially on the unknown degree to which functional variation resides in recognisable exons and evolutionarily conserved sequence. A hypothetical but reasonable scenario might be one in which trait-causing variation is equally distributed between exons plus conserved sequence, and the rest of the genome. In this scenario, our analysis suggests that a tagging approach that captures variation in exons and conserved sequence provides only modestly better coverage of putatively causal variation than does anonymous tagging. In HapMap CEU samples (with northern and western European ancestry), we observed roughly equivalent coverage for equal investment for both tagging strategies.

Young-onset type 2 diabetes families are the major contributors to genetic loci in the Diabetes UK Warren 2 genome scan and identify putative novel loci on chromosomes 8q21, 21q22, and 22q11.

A young onset of type 2 diabetes is likely to result, in part, from greater genetic susceptibility. Young-onset families may therefore represent a group in which genes are more easily detectable by linkage. To test this hypothesis, we conducted age at diagnosis (AAD) stratified linkage analyses in the Diabetes UK Warren 2 sibpairs. In the previously published unstratified analysis, evidence for linkage (logarithm of odds [LOD] >1.18) was found at seven loci. The LOD scores at these seven loci were higher in the 245 families with AAD <55 years (L55) compared with the 328 families with AAD >55 years (G55). Five of these seven loci (1q24-25, 5q13, 8p21-22, 8q24.2, and 10q23.2) had LOD scores >1.18 in the L55 subset but only one (8p21-22) did in the G55 subset. Two additional loci (8q21.13 and 21q22.2) showed evidence for linkage in the L55 subset alone. Another locus (22q11) showed evidence for linkage in a subset of families with AAD <45 years. Using a locus-counting approach, the L55 subset had significantly more loci (P approximately 0.01) than expected under the null hypothesis of no linkage across the LOD score range 0.59-3.0. In contrast, the G55 subset contained no more susceptibility loci than that expected by chance. In conclusion, young-onset families provide both disproportionate evidence for linkage to known loci and evidence for additional novel loci. Our data confirm our hypothesis that families segregating young-onset type 2 diabetes represent a more powerful resource for defining susceptibility genes by linkage.

Association and haplotype analysis of the insulin-degrading enzyme (IDE) gene, a strong positional and biological candidate for type 2 diabetes susceptibility.

The gene for insulin-degrading enzyme (IDE) represents a strong positional and biological candidate for type 2 diabetes susceptibility. IDE maps to chromosome 10q23.3, a region linked to diabetes in several populations; the rat homolog has been directly implicated in diabetes susceptibility; and known functions of IDE support an important role in glucose homeostasis. We sought evidence for association between IDE variation and diabetes by mutation screening, defining local haplotype structure, and genotyping variants delineating common haplotypic diversity. An initial case-control analysis (628 diabetic probands from multiplex sibships and 604 control subjects) found no haplotypic associations, although one variant (IDE2, -179T-->C) showed modest association with diabetes (odds ratio [OR]1.25, P = 0.03). Linkage partitioning analyses failed to support this association, but provided borderline evidence for a different variant (IDE10, IVS20-405A-->G) (P = 0.06). Neither variant was associated with diabetes when replication was sought in 377 early onset diabetic subjects and 825 control subjects, though combined analysis of all typed cohorts indicated a nominally significant effect at IDE2 (OR 1.21 [1.04-1.40], P = 0.013). In the absence of convincing support for this association from linkage partitioning or analyses of continuous measures of glycemia, we conclude that analysis of over 2,400 samples provides no compelling evidence that variation in IDE contributes to diabetes susceptibility in humans.

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.

Variation within the type 2 diabetes susceptibility gene calpain-10 and polycystic ovary syndrome.

Variation within the calpain-10 gene (CAPN10) has been proposed to account for linkage to type 2 diabetes on chromosome 2q in Mexican-Americans, and associations with diabetes have been reported in several other populations. Given the epidemiological, physiological, and genetic overlap between type 2 diabetes and polycystic ovary syndrome (PCOS), CAPN10 represents a strong candidate gene for a role in PCOS susceptibility. Using both family based and case-control association resources (146 parent-offspring trios; 185 additional PCOS cases; 525 control subjects, all of European ancestry), we sought association between CAPN10 variation and PCOS, focusing on four single nucleotide polymorphism (SNP) variants (SNP-44, SNP-43; SNP-19; SNP-63). On single-locus transmission disequilibrium analysis in the 146 trios, there was nominal evidence (P = 0.03) of excess transmission of the more common allele at SNP-63. This association was not, however, replicated in the case-control analysis. No other significant associations were observed at the single-locus or haplotype level in either the transmission-disequilibrium or case-control analyses. The relative risk for the high-risk diabetes susceptibility 112/121 genotype (SNPs 43-19-63) was 0.84 (95% confidence intervals, 0.40-1.71). No associations were seen with intermediate traits of relevance to diabetes and PCOS pathogenesis. We have found no evidence from these analyses that CAPN10 gene variation influences susceptibility to PCOS.

A detailed genetic map of the chromosome 7 bronchial hyper-responsiveness locus.

Non-specific bronchial hyper-responsiveness to various inhaled stimuli is a characteristic of asthma. We have previously shown linkage of bronchial responsiveness to methacholine (measured as dose-response slope (DRS)) and the peripheral blood eosinophil count (EOS) to chromosome 7. We have now further investigated these linkages by genotyping 49 microsatellite markers across the DRS locus on chromosome 7. The markers were spaced on average 2.6 cM apart and spanned a sex averaged cumulative genetic distance of 129 cM. Multipoint linkage to DRS was bimodal and dipped at the centromere. The two peaks of linkage were close to markers D7S484 (P=0.0003) and D7S669 (P=0.006) respectively. Separate testing for linkage to paternally and maternally derived alleles showed that the linkage near D7S484 was paternally derived (P<0.00001): maternally derived alleles did not exhibit significant linkage. The results indicate that two disparate loci may be influencing asthma from chromosome 7.