Identification of Novel Genetic Variants and Comorbidities Associated With ICD-10-Based Diagnosis of Hypertrophic Cardiomyopathy Using the UK Biobank Cohort.

Objectives: To identify previously unrecognized genetic variants and clinical variables associated with the ICD-10 (International Classification of Diseases 10)-based diagnosis of hypertrophic cardiomyopathy in the UK Biobank cohort. Background: Hypertrophic cardiomyopathy (HCM) is the most common genetic cardiovascular disorder with more than 2000 known mutations in one of eight genes encoding sarcomeric proteins. However, there is considerable variation in disease manifestation, suggesting the role of additional unrecognized contributors, genetic and otherwise. There is substantial interest in the use of real-world data, such as electronic health records to better understand disease mechanisms and discover new treatment strategies, but whether ICD-10-based diagnosis can be used to study HCM genetics is unknown. Methods: In a genome-wide association study (GWAS) using the UK Biobank, we analyzed the genomes of 363 individuals diagnosed with HCM based on ICD-10 coding compared to 7,260 age, ancestry, and sex-matched controls in a 1:20 case:control design. Genetic variants were analyzed by Plink's firth logistic regression and assessed for association with HCM. We also examined 61 biomarkers and other diagnoses in the 363 HCM cases and matched controls. Results: The prevalence of ICD-10-based diagnosis of HCM in the UK Biobank cohort was 1 in 1,342, suggesting disease assignment based on the two ICD-10 codes underestimates HCM prevalence. In addition, common cardiovascular comorbidities were more prevalent in ICD-10-based HCM cases in comparison to controls. We identified two novel, non-sarcomeric genetic variants in KMT2C rs78630626, and PARD3B rs188937806 that were associated with ICD-10 codes for HCM with genome-wide significance (p < 5 x 10-8). These are associated with an increased odds ratio (OR) of ∼3.8 for being diagnosed with HCM. Minor allele frequency (MAF) of each variant was >1%. Discussion: Disease assignment based strictly on ICD-10 codes may underestimate HCM prevalence. Individuals with HCM were more frequently diagnosed with several comorbid conditions, such as hypertension, atherosclerotic heart disease, diabetes, and kidney failure, suggesting they may contribute to disease manifestation. This UK Biobank database-based GWAS identified common variants in KMT2C and PARD3B that are associated with HCM diagnosis, which may represent novel modifier genes. Our study demonstrates the feasibility and limitations of conducting phenotypic and genotypic characterization of HCM based on ICD-10 diagnosis in a large population-based cohort.

Identification of novel genetic susceptibility loci for thoracic and abdominal aortic aneurysms via genome-wide association study using the UK Biobank Cohort.

BACKGROUND: Thoracic aortic aneurysm (TAA) and abdominal aortic aneurysm (AAA) are known to have a strong genetic component. METHODS AND RESULTS: In a genome-wide association study (GWAS) using the UK Biobank, we analyzed the genomes of 1,363 individuals with AAA compared to 27,260 age, ancestry, and sex-matched controls (1:20 case:control study design). A similar analysis was repeated for 435 individuals with TAA compared to 8,700 controls. Polymorphism with minor allele frequency (MAF) >0.5% were evaluated. We identified novel loci near LINC01021, ATOH8 and JAK2 genes that achieved genome-wide significance for AAA (p-value <5x10-8), in addition to three known loci. For TAA, three novel loci in CTNNA3, FRMD6 and MBP achieved genome-wide significance. There was no overlap in the genes associated with AAAs and TAAs. Additionally, we identified a linkage group of high-frequency variants (MAFs ~10%) encompassing FBN1, the causal gene for Marfan syndrome, which was associated with TAA. In FinnGen PheWeb, this FBN1 haplotype was associated with aortic dissection. Finally, we found that baseline bradycardia was associated with TAA, but not AAA. CONCLUSIONS: Our GWAS found that AAA and TAA were associated with distinct sets of genes, suggesting distinct underlying genetic architecture. We also found association between baseline bradycardia and TAA. These findings, including JAK2 association, offer plausible mechanistic and therapeutic insights. We also found a common FBN1 linkage group that is associated with TAA and aortic dissection in patients who do not have Marfan syndrome. These FBN1 variants suggest shared pathophysiology between Marfan disease and sporadic TAA.

Baseline cardiometabolic profiles and SARS-CoV-2 infection in the UK Biobank.

BACKGROUND: SARS-CoV-2 is a rapidly spreading coronavirus responsible for the Covid-19 pandemic, which is characterized by severe respiratory infection. Many factors have been identified as risk factors for SARS-CoV-2, with much early attention being paid to body mass index (BMI), which is a well-known cardiometabolic risk factor. OBJECTIVE: This study seeks to examine the impact of additional baseline cardiometabolic risk factors including high density lipoprotein-cholesterol (HDL-C), low density lipoprotein-cholesterol (LDL-C), Apolipoprotein A-I (ApoA-I), Apolipoprotein B (ApoB), triglycerides, hemoglobin A1c (HbA1c) and diabetes on the odds of testing positive for SARS-CoV-2 in UK Biobank (UKB) study participants. METHODS: We examined the effect of BMI, lipid profiles, diabetes and alcohol intake on the odds of testing positive for SARS-Cov-2 among 9,005 UKB participants tested for SARS-CoV-2 from March 16 through July 14, 2020. Odds ratios and 95% confidence intervals were computed using logistic regression adjusted for age, sex and ancestry. RESULTS: Higher BMI, Type II diabetes and HbA1c were associated with increased SARS-CoV-2 odds (p < 0.05) while HDL-C and ApoA-I were associated with decreased odds (p < 0.001). Though the effect of BMI, Type II diabetes and HbA1c were eliminated when HDL-C was controlled, the effect of HDL-C remained significant when BMI was controlled for. LDL-C, ApoB and triglyceride levels were not found to be significantly associated with increased odds. CONCLUSION: Elevated HDL-C and ApoA-I levels were associated with reduced odds of testing positive for SARS-CoV-2, while higher BMI, type II diabetes and HbA1c were associated with increased odds. The effects of BMI, type II diabetes and HbA1c levels were no longer significant after controlling for HDL-C, suggesting that these effects may be mediated in part through regulation of HDL-C levels. In summary, our study suggests that baseline HDL-C level may be useful for stratifying SARS-CoV-2 infection risk and corroborates the emerging picture that HDL-C may confer protection against sepsis in general and SARS-CoV-2 in particular.

Baseline Cardiometabolic Profiles and SARS-CoV-2 Infection in the UK Biobank.

BACKGROUND: SARS-CoV-2 is a rapidly spreading coronavirus with a high incidence of severe upper respiratory infection that first presented in Wuhan, China in December 2019. Many factors have been identified as risk factors for SARS-CoV-2, with much attention being paid to body mass index (BMI). Little investigation has been done to investigate dysregulation of lipid profiles and diabetes, which are often comorbid in high BMI patients. OBJECTIVE: This study seeks to describe the impact of BMI, HDL, LDL, ApoA, ApoB, triglycerides, hemoglobin A1c (HbA1c), diabetes, alcohol and red wine intake on the odds of testing positive for SARS-CoV-2 in UK Biobank (UKB) study participants. METHODS: We examined the effect of BMI, lipid profiles, diabetes and alcohol intake on the odds of testing positive for SARS-Cov-2 among 9,005 UKB participants tested for SARS-CoV-2 from March 16 through July 14, 2020. Odds ratios and 95% confidence intervals were computed using logistic regression adjusted for age, sex and ancestry. RESULTS: Higher BMI, Type II diabetes and HbA1c were associated with increased SARS-CoV-2 odds (p < 0.05) while HDL and ApoA were associated with decreased odds (p < 0.001). Though the effect of BMI, Type II diabetes and HbA1c were eliminated when HDL was controlled, the effect of HDL remained significant when BMI was controlled for. Additionally, red wine intake was associated with reduced odds of testing positive for SARS-CoV-2 (p < 0.05). LDL, ApoB and triglyceride levels were not found to be significantly associated with increased odds. CONCLUSION: Elevated HDL and ApoA levels and alcohol intake, specifically red wine intake, were associated with reduced odds of testing positive for SARS-CoV-2, while higher BMI, type II diabetes and HbA1c were associated with increased odds. The effects of alcohol, BMI, type II diabetes and HbA1c levels were no longer significant after controlling for HDL, suggesting that these effects may be mediated in part through regulation of HDL levels. In summary, our study corroborates the emerging picture that high HDL levels may confer protection against SARS-CoV-2. HIGHLIGHTS: Higher baseline HDL levels were associated with reduced odds of testing positive for SARS-CoV-2.BMI, Type II diabetes and hemoglobin A1C levels were associated with elevated odds of testing positive for SARS-CoV-2, but this effect was abrogated when controlling for HDL.Red wine intake was associated with reduced odds of testing positive for SARS-CoV-2, although this effect may in part be moderated by HDL.Baseline LDL and Triglyceride levels were not associated with increased odds of testing positive for SARS-CoV-2.

Identification of Genotype Errors.

It has been documented that there exist some errors in most large genotype datasets and that an error rate of 1-2% is sufficient to lead to the distortion of map distance as well as a false conclusion of linkage (Abecasis et al., Eur J Hum Genet 9:130-134, 2001), therefore one needs to ensure that the data are as clean as possible. On the other hand, the process of data cleaning is tedious and demands effort and experience. O'Connell and Weeks implemented four error-checking algorithms in computer software called PedCheck. In this chapter, the four algorithms implemented in PedCheck are discussed with a focus on the genotype-elimination method. Furthermore, an example for four levels of error checking permitted by PedCheck is provided with the required input files. In addition, alternative algorithms implemented in other statistical computing programs are also briefly discussed.

Gene Expression Differences Between Offspring of Long-Lived Individuals and Controls in Candidate Longevity Regions: Evidence for PAPSS2 as a Longevity Gene.

Although there is compelling evidence for a genetic contribution to longevity, identification of specific genes that robustly associate with longevity has been a challenge. In order to identify longevity-enhancing genes, we measured differential gene expression between offspring of long-lived Amish (older than 90 years; cases, n = 128) and spouses of these offspring (controls, n = 121) and correlated differentially expressed transcripts with locations of longevity-associated variants detected in a prior genome-wide association study (GWAS) of survival to age 90. Expression of one of these transcripts, 3'-phosphoadenosine 5'-phosphosulfate synthase 2 (PAPSS2), was significantly higher in offspring versus controls (4×10(-4)) and this association was replicated using quantitative real-time polymerase chain reaction. PAPSS2, a sulfation enzyme located on chromosome 10, is ~80kb upstream of the PAPSS2 transcription start site. We found evidence of cis-expression for the originally reported GWAS SNP and PAPSS2 Monogenic conditions linked to PAPSS2 include andrenocortical androgen excess resulting in premature pubarche and skeletal dysplasias, both of which have premature aging features. In summary, these findings provide novel evidence for PAPSS2 as a longevity locus and illustrate the value of harnessing multiple "-omic" approaches to identify longevity candidates.

Large-scale gene-centric meta-analysis across 32 studies identifies multiple lipid loci.

Genome-wide association studies (GWASs) have identified many SNPs underlying variations in plasma-lipid levels. We explore whether additional loci associated with plasma-lipid phenotypes, such as high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC), and triglycerides (TGs), can be identified by a dense gene-centric approach. Our meta-analysis of 32 studies in 66,240 individuals of European ancestry was based on the custom ∼50,000 SNP genotyping array (the ITMAT-Broad-CARe array) covering ∼2,000 candidate genes. SNP-lipid associations were replicated either in a cohort comprising an additional 24,736 samples or within the Global Lipid Genetic Consortium. We identified four, six, ten, and four unreported SNPs in established lipid genes for HDL-C, LDL-C, TC, and TGs, respectively. We also identified several lipid-related SNPs in previously unreported genes: DGAT2, HCAR2, GPIHBP1, PPARG, and FTO for HDL-C; SOCS3, APOH, SPTY2D1, BRCA2, and VLDLR for LDL-C; SOCS3, UGT1A1, BRCA2, UBE3B, FCGR2A, CHUK, and INSIG2 for TC; and SERPINF2, C4B, GCK, GATA4, INSR, and LPAL2 for TGs. The proportion of explained phenotypic variance in the subset of studies providing individual-level data was 9.9% for HDL-C, 9.5% for LDL-C, 10.3% for TC, and 8.0% for TGs. This large meta-analysis of lipid phenotypes with the use of a dense gene-centric approach identified multiple SNPs not previously described in established lipid genes and several previously unknown loci. The explained phenotypic variance from this approach was comparable to that from a meta-analysis of GWAS data, suggesting that a focused genotyping approach can further increase the understanding of heritability of plasma lipids.

Association of the vitamin D metabolism gene CYP24A1 with coronary artery calcification.

OBJECTIVE: The vitamin D endocrine system is essential for calcium homeostasis, and low levels of vitamin D metabolites have been associated with cardiovascular disease risk. We hypothesized that DNA sequence variation in genes regulating vitamin D metabolism and signaling pathways might influence variation in coronary artery calcification (CAC). METHODS AND RESULTS: We genotyped single-nucleotide polymorphisms (SNPs) in GC, CYP27B1, CYP24A1, and VDR and tested their association with CAC quantity, as measured by electron beam computed tomography. Initial association studies were carried out in a discovery sample comprising 697 Amish subjects, and SNPs nominally associated with CAC quantity (4 SNPs in CYP24A1, P=0.008 to 0.00003) were then tested for association with CAC quantity in 2 independent cohorts of subjects of white European ancestry (Genetic Epidemiology Network of Arteriopathy study [n=916] and the Penn Coronary Artery Calcification sample [n=2061]). One of the 4 SNPs, rs2762939, was associated with CAC quantity in both the Genetic Epidemiology Network of Arteriopathy (P=0.007) and Penn Coronary Artery Calcification (P=0.01) studies. In all 3 populations, the rs2762939 C allele was associated with lower CAC quantity. Metaanalysis for the association of this SNP with CAC quantity across all 3 studies yielded a P value of 2.9×10(-6). CONCLUSIONS: A common SNP in the CYP24A1 gene was associated with CAC quantity in 3 independent populations. This result suggests a role for vitamin D metabolism in the development of CAC quantity.

Evaluation of self-reported ethnicity in a case-control population: the stroke prevention in young women study.

BACKGROUND: Population-based association studies are used to identify common susceptibility variants for complex genetic traits. These studies are susceptible to confounding from unknown population substructure. Here we apply a model-based clustering approach to our case-control study of stroke among young women to examine if self-reported ethnicity can serve as a proxy for genetic ancestry. FINDINGS: A population-based case-control study of stroke among women aged 15-49 identified 361 cases of first ischemic stroke and 401 age-comparable control subjects. Thirty single nucleotide polymorphisms (SNPs) throughout the genome unrelated to stroke risk and with established ancestry-based allele frequency differences were genotyped in all participants. The Structure program was used to iteratively evaluate for K = 1 to 5 potential genetic-based subpopulations. Evaluating the population as a whole, the Structure output plateaued at K = 2 clusters. 98% of self-reported Caucasians had an estimated probability >/=50% of belonging to Cluster 1, while 94% of self-reported African-Americans had an estimated probability >/=50% of belonging to Cluster 2. Stratifying the participants by self-reported ethnicity and repeating the analyses revealed the presence of two clusters among Caucasians, suggesting that potential substructure may exist. CONCLUSIONS: Among our combined sample of African-American and Caucasian participants there is no large unknown subpopulation and self-reported ethnicity can serve as a proxy for genetic ancestry. Ethnicity-specific analyses indicate that population substructure may exist among the Caucasian participants indicating that further studies are warranted.

Relation of candidate genes that encode for endothelial function to migraine and stroke: the Stroke Prevention in Young Women study.

BACKGROUND AND PURPOSE: Migraine with aura is a risk factor for ischemic stroke, but the mechanism by which these disorders are associated remains unclear. Both disorders exhibit familial clustering, which may imply a genetic influence on migraine and stroke risk. Genes encoding for endothelial function are promising candidate genes for migraine and stroke susceptibility because of the importance of endothelial function in regulating vascular tone and cerebral blood flow. METHODS: Using data from the Stroke Prevention in Young Women study, a population-based case-control study including 297 women aged 15 to 49 years with ischemic stroke and 422 women without stroke, we evaluated whether polymorphisms in genes regulating endothelial function, including endothelin-1 (EDN), endothelin receptor type B (EDNRB), and nitric oxide synthase-3 (NOS3), confer susceptibility to migraine and stroke. RESULTS: EDN SNP rs1800542 and rs10478723 were associated with increased stroke susceptibility in whites (OR, 2.1; 95% CI, 1.1-4.2 and OR, 2.2; 95% CI, 1.1-4.4; P=0.02 and 0.02, respectively), as were EDNRB SNP rs4885493 and rs10507875, (OR, 1.7; 95% CI, 1.1-2.7 and OR, 2.4; 95% CI, 1.4-4.3; P=0.01 and 0.002, respectively). Only 1 of the tested SNP (NOS3 rs3918166) was associated with both migraine and stroke. CONCLUSIONS: In our study population, variants in EDN and EDNRB were associated with stroke susceptibility in white but not in black women. We found no evidence that these genes mediate the association between migraine and stroke.

Association of a common nonsynonymous variant in GLUT9 with serum uric acid levels in old order amish.

OBJECTIVE: Uric acid is the primary end product of purine metabolism. Increased serum uric acid levels have been associated with gouty arthritis as well as with a variety of cardiovascular-related phenotypes. This study was undertaken to investigate associations between uric acid levels and single-nucleotide polymorphisms (SNPs). METHODS: A 500,000-SNP genome-wide association study of serum uric acid levels was performed in a cohort of Old Order Amish from Lancaster County, Pennsylvania. RESULTS: The scan confirmed a previously identified region on chromosome 4 to be strongly associated with uric acid levels (P = 4.2 x 10(-11) for rs10489070). Followup genotyping revealed that a nonsynonymous coding SNP (Val253Ile; rs16890979) in GLUT9 was most strongly associated with uric acid levels, with each copy of the minor allele associated with a decrease of 0.47 mg/dl in the uric acid level (95% confidence interval 0.31-0.63 [P = 1.43 x 10(-11)]). The effect of this variant tended to be stronger in women than in men (P = 0.16 for sex-genotype interaction). The genotype effect was not modified by the inclusion of several cardiovascular risk factors, suggesting that GLUT9 is directly related to uric acid homeostasis. The SNP identified in the genome-wide scan in the Amish population (rs10489070) was also significantly associated with gout in the Framingham Heart Study (P = 0.004). CONCLUSION: Our findings indicate that GLUT9, which is expressed in the kidney, may be a novel regulator of uric acid elimination and that a common nonsynonymous variant in this gene contributes to abnormalities in uric acid homeostasis and gout.

Physical activity and the association of common FTO gene variants with body mass index and obesity.

BACKGROUND: Common FTO (fat mass and obesity associated) gene variants have recently been associated with body mass index (BMI) and obesity in several large studies. The role of lifestyle factors (such as physical activity) in those with an underlying FTO genetic predisposition is unknown. METHODS: To determine if FTO variants are associated with BMI in Old Order Amish (OOA) individuals, and to further determine whether the detrimental associations of FTO gene variants can be lessened by increased physical activity, a total of 704 healthy OOA adults were selected from the Heredity and Phenotype Intervention (HAPI) Heart Study, an investigation of gene x environment interactions in cardiovascular disease, for whom objective quantified physical activity measurements were available and for whom 92 single-nucleotide polymorphisms (SNPs) in FTO were genotyped. RESULTS: Twenty-six FTO SNPs were associated with BMI (P = .04 to <.001), including rs1477196 (P < .001) and rs1861868 (P < .001), 2 SNPs in moderate linkage disequilibrium in the OOA (D' = 0.82; r(2) = 0.36). Stratified analyses of rs1861868 revealed its association with BMI to be restricted entirely to those subjects with low sex- and age-adjusted physical activity scores (P < .001); in contrast, the SNP had no effect on those with above-average physical activity scores (P = .29), with the genotype x physical activity interaction achieving statistical significance (P = .01). Similar evidence for interaction was also obtained for rs1477196. CONCLUSIONS: Our results strongly suggest that the increased risk of obesity owing to genetic susceptibility by FTO variants can be blunted through physical activity. These findings emphasize the important role of physical activity in public health efforts to combat obesity, particularly in genetically susceptible individuals.

Homozygosity by descent mapping of blood pressure in the Old Order Amish: evidence for sex specific genetic architecture.

BACKGROUND: High blood pressure is a well established risk factor for morbidity and mortality acting through heart disease, stroke and cardiovascular disease. Genome wide scans have linked regions of nearly every human chromosome to blood pressure related traits. We have capitalized on beneficial qualities of the Old Order Amish of Lancaster, PA, a closed founder population with a relatively small number of founders, to perform a genome wide homozygosity by descent mapping scan. Each individual in the study has a non zero probability of consanguinity. Systolic and diastolic blood pressures are shown to have appreciable dominance variance components. RESULTS: Areas of two chromosomes were identified as suggestive of linkage to SBP and 5 areas to DBP in either the overall or sex specific analyses. The strongest evidence for linkage in the overall sample was to Chromosome 18q12 (LOD = 2.6 DBP). Sex specific analyses identified a linkage on Chromosome 4p12-14 (LOD in men only = 3.4 SBP). At Chromosome 2q32-33, an area where we previously reported significant evidence for linkage to DBP using a conventional identity by descent approach, the LOD was 1.4; however an appreciable sex effect was observed with men accounting for most of the linkage (LOD in men only = 2.6). CONCLUSION: These results add evidence to a sex specific genetic architecture to blood pressure related traits, particularly in regions of linkage on chromosome 2, 4 and 18.

Identification of novel candidate genes for type 2 diabetes from a genome-wide association scan in the Old Order Amish: evidence for replication from diabetes-related quantitative traits and from independent populations.

OBJECTIVE: We sought to identify type 2 diabetes susceptibility genes through a genome-wide association scan (GWAS) in the Amish. RESEARCH DESIGN AND METHODS: DNA from 124 type 2 diabetic case subjects and 295 control subjects with normal glucose tolerance were genotyped on the Affymetrix 100K single nucleotide polymorphism (SNP) array. A total of 82,485 SNPs were tested for association with type 2 diabetes. Type 2 diabetes-associated SNPs were further prioritized by the following: 1) associations with 5 oral glucose tolerance test (OGTT) traits in 427 nondiabetic Amish subjects, and 2) in silico replication from three independent 100L SNP GWASs (Framingham Heart Study Caucasians, Pima Indians, and Mexican Americans) and a 500K GWAS in Scandinavians. RESULTS: The strongest association (P = 1.07 x 10(-5)) was for rs2237457, which is located in growth factor receptor-bound protein 10 (Grb10), an adaptor protein that regulate insulin receptor signaling. rs2237457 was also strongly associated with OGTT glucose area under the curve in nondiabetic subjects (P = 0.001). Of the 1,093 SNPs associated with type 2 diabetes at P < 0.01, 67 SNPs demonstrated associations with at least one OGTT trait in nondiabetic individuals; 80 SNPs were nominally associated with type 2 diabetes in one of the three independent 100K GWASs, 3 SNPs (rs2540317 in MFSD9, rs10515353 on chromosome 5, and rs2242400 in BCAT1 were associated with type 2 diabetes in more than one population), and 11 SNPs were nominally associated with type 2 diabetes in Scandinavians. One type 2 diabetes-associated SNP (rs3845971, located in FHIT) showed replication with OGTT traits and also in another population. CONCLUSIONS: Our GWAS of type 2 diabetes identified several gene variants associated with type 2 diabetes, some of which are worthy of further study.

Quantitative trait loci for BMD identified by autosome-wide linkage scan to chromosomes 7q and 21q in men from the Amish Family Osteoporosis Study.

UNLABELLED: Using autosome-wide linkage analysis in 964 Amish, strong evidence was found for the presence of genes affecting hip and spine BMD in men on chromosomes 7q31 and 21q22 (LOD = 4.15 and 3.36, respectively). INTRODUCTION: BMD is highly heritable, with genetic factors accounting for 60-88% of variation. The goal of this study was to localize genes contributing to BMD variation. MATERIALS AND METHODS: The Amish Family Osteoporosis Study was designed to identify genes affecting bone health. The Amish are a genetically closed population with a homogeneous lifestyle. BMD was measured at the spine, hip, and radius using DXA in 964 participants (mean age, 50.2 +/- 16.3 [SD] years; range, 18-99 years) from large multigenerational families. Genotyping of 731 highly polymorphic microsatellite markers (average spacing of 5.4 cM) and autosome-wide multipoint linkage analysis were performed. RESULTS: In the overall study population, no strong evidence for linkage was detected to any chromosomal region (peak LOD: 2.11 for radius BMD on chromosome 3q26). In a subgroup analysis of men (n = 371), strong evidence was detected for a quantitative trait locus (QTL) influencing BMD variation on chromosome 7q31 at the total hip (LOD = 4.15) and femoral neck (LOD = 3.09) and for a second QTL influencing spine BMD at 21q22 (LOD = 3.36). Suggestive evidence of linkage was found in men for a QTL at 12q24 affecting total hip BMD (LOD = 2.60) and at 18p11 for femoral neck (LOD = 2.07), and in women (n = 593) at 1p36 for femoral neck BMD (LOD = 2.02) and at 1q21 for spine BMD (LOD = 2.11). In age subgroup analyses, suggestive evidence for linkage was found for those <50 years of age (n = 521) on chromosomes 11q22 and 14q23 (LODs = 2.11 and 2.16, respectively) and for those >50 years of age (n = 443) on 3p25.2 (LOD = 2.32). CONCLUSIONS: These results strongly suggest the presence of genes affecting hip and spine BMD in men on chromosomes 7q31 and 21q22. Modest evidence was found for genes affecting BMD in women on chromosomes 1p36 and 1q21 and in men at 12q24, replicating results from other populations.

The pseudohypoparathyroidism type lb locus is linked to a region including GNAS1 at 20q13.3.

Pseudohypoparathyroidism (PHP) is characterized by biochemical hypoparathyroidism with elevated parathyroid hormone levels owing to reduced target tissue responsiveness to parathyroid hormone. Patients with PHP la have somatic defects termed Albright's hereditary osteodystrophy (AHO) and exhibit resistance to additional hormones because of heterozygous mutations in the GNAS1 gene that lead to a generalized deficiency of the a subunit of Gs, the heterotrimeric G protein that couples receptors to adenylyl cyclase. By contrast, patients with PHP 1b lack AHO and have selective parathyroid hormone (PTH) resistance, presumably because of an imprinting defect that impairs expression of G(s)alpha in the proximal renal tubule. Although an epigenetic defect in GNAS1 has been identified in subjects with PHP1b, the genetic defect is unknown. To define the genetic defect in PHP 1b, we performed a genome-wide linkage analysis in five multi-generational PHP lb families. Of the 408 polymorphic microsatellite markers examined, markers located on chromosome 20q13.3, the region containing GNAS1, demonstrated linkage to PHP lb. Fine-mapping and multipoint linkage analysis of this region demonstrated linkage to a 5.7-cM region between 907rep2 and the telomere. Haplotype analysis established that affected individuals shared a 5-cM region including part of the GNAS1 gene to the telomere. Our data confirm that PHP1b is linked to a region that includes GNAS1, and further refine the locus, although the primary genetic mutation(s) that causes defective imprinting of GNAS1 remains undefined.