Genome-wide analysis of mitochondrial DNA copy number reveals loci implicated in nucleotide metabolism, platelet activation, and megakaryocyte proliferation.

Mitochondrial DNA copy number (mtDNA-CN) measured from blood specimens is a minimally invasive marker of mitochondrial function that exhibits both inter-individual and intercellular variation. To identify genes involved in regulating mitochondrial function, we performed a genome-wide association study (GWAS) in 465,809 White individuals from the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) consortium and the UK Biobank (UKB). We identified 133 SNPs with statistically significant, independent effects associated with mtDNA-CN across 100 loci. A combination of fine-mapping, variant annotation, and co-localization analyses was used to prioritize genes within each of the 133 independent sites. Putative causal genes were enriched for known mitochondrial DNA depletion syndromes (p = 3.09 × 10-15) and the gene ontology (GO) terms for mtDNA metabolism (p = 1.43 × 10-8) and mtDNA replication (p = 1.2 × 10-7). A clustering approach leveraged pleiotropy between mtDNA-CN associated SNPs and 41 mtDNA-CN associated phenotypes to identify functional domains, revealing three distinct groups, including platelet activation, megakaryocyte proliferation, and mtDNA metabolism. Finally, using mitochondrial SNPs, we establish causal relationships between mitochondrial function and a variety of blood cell-related traits, kidney function, liver function and overall (p = 0.044) and non-cancer mortality (p = 6.56 × 10-4).

Transcobalamin 2 variant associated with poststroke homocysteine modifies recurrent stroke risk.

OBJECTIVES: The Vitamin Intervention for Stroke Prevention trial found an association between baseline poststroke homocysteine (Hcy) and recurrent stroke. We investigated genes for enzymes and cofactors in the Hcy metabolic pathway for association with Hcy and determined whether associated single nucleotide polymorphisms (SNPs) influenced recurrent stroke risk. METHODS: Eighty-six SNPs in 9 candidate genes (BHMT1, BHMT2, CBS, CTH, MTHFR, MTR, MTRR, TCN1, and TCN2) were genotyped in 2,206 subjects (83% European American). Associations with Hcy measures were assessed using linear regression models assuming an additive genetic model, adjusting for age, sex, and race and additionally for baseline Hcy when postmethionine load change was assessed. Associations with recurrent stroke were evaluated using survival analyses. RESULTS: Five SNPs in the transcobalamin 2 (TCN2) gene were associated with baseline Hcy (false discovery rate [FDR]-adjusted p = 0.049). TCN2 SNP rs731991 was associated with recurrent stroke risk in the low-dose arm of the trial under a recessive model (log-rank test p = 0.009, hazard ratio 0.34). Associations with change in postmethionine load Hcy levels were found with 5 SNPs in the cystathionine ß-synthase (CBS) gene (FDR-adjusted p < 0.031). CONCLUSIONS: TCN2 variants contribute to poststroke Hcy levels, whereas variants in the CBS gene influence Hcy metabolism. Variation in the TCN2 gene also affects recurrent stroke risk in response to cofactor therapy.

A genome-wide linkage scan for iron phenotype quantitative trait loci: the HEIRS Family Study.

Iron overload phenotypes in persons with and without hemochromatosis are variable. To investigate this further, probands with hemochromatosis or evidence of elevated iron stores and their family members were recruited for a genome-wide linkage scan to identify potential quantitative trait loci (QTL) that contribute to variation in transferrin saturation (TS), unsaturated iron-binding capacity (UIBC), and serum ferritin (SF). Genotyping utilized 402 microsatellite markers with average spacing of 9 cM. A total of 943 individuals, 64% Caucasian, were evaluated from 174 families. After adjusting for age, gender, and race/ethnicity, there was evidence for linkage of UIBC to chromosome 4q logarithm of the odds (LOD) = 2.08, p = 0.001) and of UIBC (LOD = 9.52), TS (LOD = 4.78), and SF (LOD = 2.75) to the chromosome 6p region containing HFE (each p < 0.0001). After adjustments for HFE genotype and other covariates, there was evidence of linkage of SF to chromosome 16p (LOD = 2.63, p = 0.0007) and of UIBC to chromosome 5q (LOD = 2.12, p = 0.002) and to chromosome 17q (LOD = 2.19, p = 0.002). We conclude that these regions should be considered for fine mapping studies to identify QTL that contribute to variation in SF and UIBC.

A genome-wide linkage scan for genes controlling variation in urinary albumin excretion in type II diabetes.

The main hallmark of diabetic nephropathy is elevation in urinary albumin excretion. We performed a genome-wide linkage scan in 63 extended families with multiple members with type II diabetes. Urinary albumin excretion, measured as the albumin-to-creatinine ratio (ACR), was determined in 426 diabetic and 431 nondiabetic relatives who were genotyped for 383 markers. The data were analyzed using variance components linkage analysis. Heritability (h2) of ACR was significant in diabetic (h2=0.23, P=0.0007), and nondiabetic (h2=0.39, P=0.0001) relatives. There was no significant difference in genetic variance of ACR between diabetic and nondiabetic relatives (P=0.16), and the genetic correlation (rG=0.64) for ACR between these two groups was not different from 1 (P=0.12). These results suggested that similar genes contribute to variation in ACR in diabetic and nondiabetic relatives. This hypothesis was supported further by the linkage results. Support for linkage to ACR was suggestive in diabetic relatives and became significant in all relatives for chromosome 22q (logarithm of odds, LOD=3.7) and chromosome 7q (LOD=3.1). When analyses were restricted to 59 Caucasian families, support for linkage in all relatives increased and became significant for 5q (LOD=3.4). In conclusion, genes on chromosomes 22q, 5q and 7q may contribute to variation in urinary albumin excretion in diabetic and nondiabetic individuals.

Correlation of proband and sibling stroke latency: the SWISS Study.

The authors found a correlation between the age at which probands experience an incident stroke and the age at which their siblings experience an incident stroke (r = 0.68; p < 0.0001). Proband-sibling incident stroke latency correlations were observed in analyses restricted to siblings concordant for smoking (r = 0.68; p < 0.0001), diabetes (r = 0.73; p < 0.0001), and hypertension (r = 0.63; p < 0.0001). In the authors' cohort of affected sibling pairs, inherited factors were important determinants of incident ischemic stroke latency.

Familial aggregation of coronary artery calcium in families with type 2 diabetes.

Type 2 diabetes is widely recognized as a major risk factor for atherosclerotic cardiovascular disease, including subclinical atherosclerosis as measured by noninvasive procedures. However, the role of genetic factors that contribute to various measures of subclinical atherosclerosis is largely unknown. We hypothesize that subclinical atherosclerosis, measured as coronary artery calcification (CAC), will be extensive in individuals with type 2 diabetes and that its presence depends on both genetic and environmental factors. The genetic factors should result in the familial aggregation of CAC. To determine the extent of familial aggregation of CAC in the presence of type 2 diabetes, we studied 122 individuals with type 2 diabetes (mean age 60 years) and 13 individuals without diabetes in 56 families. CAC was measured by fast-gated helical computed tomography. Other measured factors included blood pressure, body size, lipids, HbA1c, and self-reported medical history. To test for an association between CAC and these factors while accounting for the potential familial correlation of CAC, generalized estimating equations were used. CAC was detectable in 80% of individuals with diabetes (median score 84, range 0-5,776). Extent of CAC, adjusted for age, was positively associated with male sex (P = 0.0003), reduced HDL (P = 0.02), albumin-to-creatinine ratio (P = 0.008), and cigarette pack-years (P = 0.03). CAC was also positively associated with a history of angina, myocardial infarction, stroke, and vascular procedures (all P < 0.01). HbA1c and fasting glucose were positively, but nonsignificantly, associated with the extent of CAC (P = 0.14 and 0.08, respectively). CAC, adjusted for age, sex, race, and diabetes status, was heritable (h2 = 0.50; P = 0.009). In multivariate analysis with additional adjustment for HDL, BMI, hypertension, and smoking, h2 = 0.40 (P = 0.038). These results suggest that strong (independent) genetic factors as well as environmental factors contribute to the variance of CAC in individuals with type 2 diabetes. In these data, CAC seems heritable and may serve as an important feature in designing studies to map genes contributing to both atherosclerosis and type 2 diabetes.

Association of autoimmune thyroid disease with microsatellite markers for the thyrotropin receptor gene and CTLA-4 in Japanese patients.

In a previous study we identified a microsatellite marker near the thyrotropin receptor (TSHR) gene. Studies with this marker, TSHR-CA, revealed a significant association between autoimmune thyroid disease (AITD) in Japanese patients and one specific allele (allele 1; 180 base pair [bp]) of the microsatellite sequence. In addition, weak evidence for association of AITD with two alleles of the CTLA-4 gene was observed. In the present study, TSHR-CA has been mapped to approximately 600 kb of the TSHR gene using radiation hybrid mapping. TSHR-CA and another TSHR microsatellite marker, TSHR-AT, which is located in intron 2 of TSHR gene, were genotyped in a set of 349 unrelated Japanese AITD patients and 218 Japanese controls. The TSHR-AT marker showed association in this Japanese AITD population with a significant increase in allele 5 (294 bp; p < 0.05) and a significant decrease in allele 7 (298 bp; p < 0.05). The association of allele 5 of TSHR-AT was also significant in hypothyroid patients (thyrotropin-binding inhibitory immunoglobulin-positive [TBII+], P < 0.01; thyrotropin-binding inhibitory immunoglobulin-negative [TBII-], p < 0.05). The association of allele 7 of TSHR-AT were also significant for the hypothyroid TBII+ patients (p < 0.05). The CTLA-4 gene was also genotyped in this expanded set of Japanese AITD patients and controls. Association between AITD susceptibility and allele 2 (102 bp; p < 0.01) and allele 4 (106 bp; p < 0.01) were observed. These associations were also observed with GD patients (allele 2, p < 0.01; allele 4, p < 0.01). Associations with TSHR-CA were observed for Hashimoto's thyroiditis (HT) patients with respect to alleles 3 (179 bp; p < 0.05) and 5 (175 bp; p < 0.05) and with hypothyroid TBII- patients for allele 4 (177 bp; p < 0.05). The presence of specific alleles of TSHR-CA, TSHR-AT, and CTLA-4 contribute significant increase in risk of development of AITD. These results confirm and expand on our previous study suggesting that alleles of the TSHR and CTLA-4 genes, or genes near them contribute to AITD susceptibility and set the stage for future studies of interactions between these genes and AITD.

Evidence for major genes influencing pulmonary function in the NHLBI family heart study.

Segregation analysis was performed on the pulmonary measures forced expiratory volume in one second (FEV1), forced vital capacity (FVC), and the ratio of FEV1/FVC in 455 randomly ascertained families from the NHLBI Family Heart Study (FHS). Gender specific standardized residuals were used as the phenotypic variable in both familial correlation and segregation analyses. These residuals represented adjustments for the effects of age, age(2), age(3), Body Mass Index (BMI, kg/m(2)), height, the ratio of waist to hip measurements (WHR), the presence of coronary heart disease, smoking history, and pack years for current smokers. Sibling correlations were not different from parent-offspring correlations for all three traits, and heritability estimates for FEV1, FVC, and the FEV1/FVC ratio were 0. 515, 0.540, and 0.449, respectively. Segregation analysis of FEV1, a trait that measures airflow, indicated that a dominant major gene best fits the data, although a residual familial correlation supports the presence of an additional polygenic or common environmental component. For FVC, a trait that measures lung volume, alternative models could not be statistically differentiated, but the transmission probabilities do not support a Mendelian major gene. The best model for FEV1/FVC ratio is a non-Mendelian codominant model, perhaps due to the mixing of the individual underlying distributions influencing airflow and lung volume. These results support the hypothesis that complex relationships exist for lung function traits and that multiple genes and environmental factors influence lung function.

BRCA1 susceptibility markers and postmenopausal breast cancer: the Iowa Women's Health Study.

Much research on early-onset breast cancer families has been performed and has shown that breast cancer in many of these families is linked to either BRCA1 or BRCA2. Fewer studies have examined the role of genetic predisposition in postmenopausal breast cancer. A nested case-control family study of breast cancer was conducted within the Iowa Women's Health Study, a population-based prospective study of 41,836 postmenopausal women. Probands were 251 incident cases diagnosed between 1988 and 1989. Three-generation pedigrees were developed through mailed questionnaires. From this collection of pedigrees, thirteen were identified for more detailed genetic analysis. Sibling-pair linkage analyses were performed using polymorphic markers in candidate regions in these 13 families with multiple cases of breast and other cancers. Four of the DNA markers are located on chromosome 17, and two of these (D17S579 and THRA1) flank the BRCA1 locus. Significant evidence for linkage to D17S579 was obtained in the total sample, in a model without inclusion of covariates or age at onset (P = 0.005), and in a model adjusted for five measured covariates and for variable age at onset (P = 0.008). Complete sequencing of the BRCA1 gene in these families, including all intron/exon boundaries, failed to reveal any mutations in 24 women with breast cancer from the 13 families. These data suggest that in some families identified by postmenopausal breast cancer cases, breast cancer risk may be mediated by a gene (or genes) in the BRCA1 region, but not BRCA1 itself.

Twinship and risk of postmenopausal breast cancer.

BACKGROUND: Intrauterine exposure to high levels of endogenous estrogens has been hypothesized to increase the risk of breast cancer. Because estrogens and other pregnancy hormones are substantially elevated in twin pregnancies, and possibly more so in dizygotic twin pregnancies, we evaluated the association between aspects of twin membership (i.e., belonging to a twin pair) and the risk of breast cancer. METHODS: In a cohort of 29 197 postmenopausal Iowa women with no prior diagnosis of cancer (except for nonmelanoma skin cancer), breast cancer risk factors were determined by use of a mailed questionnaire in 1986 (baseline); twin membership, sex of the twin, and zygosity were determined by use of a follow-up questionnaire in 1992. RESULTS: Within the cohort, 1.8% (n = 538) of the women reported being a twin; of these, 24% (n = 130) were monozygotic twins, 63% (n = 337) were dizygotic twins, and 13% (n = 71) did not know their zygosity. From 1986 through 1996, 1230 breast cancers in the cohort were ascertained by linkage to the Iowa Cancer Registry. Compared with singletons, women who belonged to a twin pair were at elevated risk of breast cancer (multivariate-adjusted risk ratio [RR] = 1.72; 95% confidence interval [CI] = 1.22-2.42), with adjustment for educational level, family history of breast cancer, height, body mass index, body fat distribution, age at menarche, age at first live birth, use of hormone replacement therapy, and alcohol use. Multivariate-adjusted risk was elevated (in comparison with singletons) if the sex of the other twin was female (RR = 1.82; 95% CI = 1.20-2.75); however, this risk was limited to female dizygotic twins (RR = 2.14; 95% CI = 1. 21-3.79), since no excess risk was evident for monozygotic twins (RR = 1.04; 95% CI = 0.43-2.50). The risk to women with a male twin was also elevated (RR = 1.49; 95% CI = 0.80-2.78) in comparison with singletons, but this estimate was not statistically significant. CONCLUSIONS: This cohort study lends further support to the theory that there are important intrauterine influences on carcinogenesis of the breast.

Human Na+/H+ exchanger genes : identification of polymorphisms by radiation hybrid mapping and analysis of linkage in end-stage renal disease.

The Na+/H+ exchangers (NHEs) are membrane-bound transporters that catalyze the electro-neutral movement of extracellular Na+ for intracellular H+. NHE genes play a critical role in pH homeostasis and cellular volume regulation and can be considered candidate genes for essential hypertension and renal disease. This study was performed to determine whether the NHE genes contributed to genetic susceptibility in end-stage renal disease (ESRD). To date, 5 isoforms of NHE have been cloned in mammals (NHE1 to NHE5). The complementary DNA (cDNA) sequences of NHE1 to NHE3 and NHE5 are known in humans. Because the chromosomal structure of the NHE genes is unknown, we used cDNA sequences to design polymerase chain reaction primers for use in radiation hybrid mapping. Radiation hybrid mapping of NHE genes identified nearby polymorphic markers for NHE1 to NHE3 (NHE1: D1S197, D1S2677; NHE2: D2S373, D2S1789; and NHE3: D5S678, D5S2005). We used these markers, and other previously identified polymorphic markers for NHE5, in linkage and association analyses of ESRD. The NHE1 to NHE3 and NHE5 loci did not demonstrate evidence for linkage to ESRD. However, NHE5 showed significant evidence for association (P

Mutations in the gene encoding KRIT1, a Krev-1/rap1a binding protein, cause cerebral cavernous malformations (CCM1).

Cerebral cavernous malformations (CCM) are congenital vascular anomalies of the brain that can cause significant neurological disabilities, including intractable seizures and hemorrhagic stroke. One locus for autosomal dominant CCM ( CCM1 ) maps to chromosome 7q21-q22. Recombination events in linked family members define a critical region of approximately 2 Mb and a shared disease haplotype associated with a presumed founder effect in families of Mexican-American descent points to a potentially smaller region of interest. Using a genomic sequence-based positional cloning strategy, we have identified KRIT1, encoding a protein that interacts with the Krev-1/rap1a tumor suppressor, as the CCM1 gene. Seven different KRIT1 mutations have been identified in 23 distinct CCM1 families. The identical mutation is present in 16 of 21 Mexican-American families analyzed, substantiating a founder effect in this population. Other Mexican-American and non-Hispanic Caucasian CCM1 kindreds harbor other KRIT1 mutations. Identification of a common Mexican-American mutation has potential clinical significance for presymptomatic diagnosis of CCM in this population. In addition, these data point to a key role for the Krev-1/rap1a signaling pathway in angiogenesis and cerebrovascular disease.

Is diabetic nephropathy inherited? Studies of glomerular structure in type 1 diabetic sibling pairs.

Only a minority of patients with type 1 diabetes develop diabetic nephropathy (DN). Poor glycemic control cannot fully explain DN risk, and family studies suggest genetic susceptibility factors. To understand familial DN concordance, we evaluated glomerular structure in families with type 1 diabetic sibling pairs. Kidney function and biopsy studies were performed in 21 probands (P) (first to develop diabetes) and 21 siblings (S) (second to develop diabetes), most with normal urinary albumin excretion rates (UAER). Glomerular structure was measured by morphometry. Intrafamilial correlation was estimated by one-way random-effects ANOVA and by mixed-effects ANOVA, adjusting for age and duration of diabetes. Diabetes duration was, by definition, longer in P than in S, while age and sex were similar. HbA1c over 5 years and blood pressure were not different in P and S and were without familial effect. UAER was greater in P than in S (P < 0.05), with strong familial effect (P = 0.03). A strong concordance among siblings for mesangial fractional volume (P < or = 0.01) remained significant after adjustment for diabetes duration and age (P = 0.04). Results were similar for mesangial cell (P = 0.01; adjusted P = 0.04) and mesangial matrix fractional volumes (P < 0.01; adjusted P = 0.06). There was also clustering of the patterns of glomerular lesions. For example, if P had relatively marked glomerular basement membrane thickening compared with mesangial matrix expansion, S had a similar pattern (chi2, P < 0.025). Strong concordance in severity and patterns of glomerular lesions in type 1 diabetic siblings, despite lack of concordance in glycemia, supports an important role for genetic factors in DN risk.

Ex vivo and in vivo adenovirus-mediated gene therapy strategies induce a systemic anti-tumor immune defence in the B16 melanoma model.

The efficacy of adenovirus-mediated gene therapy for treatment of metastatic B16 melanomas, established in syngeneic C57BL/6 mice, was assessed via an ex vivo cytokine vaccine approach or via an in vivo strategy utilizing combination cytokine/herpes simplex virus-thymidine kinase (HSV-tk) suicide gene delivery and treatment with ganciclovir (GCV). In the ex vivo tumor vaccine approach, B16 melanoma cells, transduced in vitro by adenovirus containing either interleukin (IL)-2, granulocyte-macrophage colony stimulating factor (GM-CSF), or tumor necrosis factor-alpha cytokine genes and gamma irradiated, were subcutaneously injected into the flank and a distant subcutaneous challenge injection of unmodified B16 melanoma cells was performed 15 d later. Significant reductions in challenge tumor volume were observed in the IL-2 group (75% reduction; p = 0.02) and in the GM-CSF group (88% reduction; p = 0.0006), whereas the effect for tumor necrosis factor-alpha was not statistically significant. In the in vivo treatment of established melanomas, this cytokine approach was combined with a suicide gene therapy and subcutaneous B16 melanomas were directly injected with (i) IL-2/recombinant, replication-deficient adenovirus (adv) and thymidine kinase (tk)/adv, (ii) GM-CSF/adv, IL-2/adv, and tk/adv, or (iii) control beta-galactosidase (beta-gal)/adv and tk/adv. After intraperitoneal application of GCV (10 mg per kg) for 6 d, the residual tumor masses were excised and the animals challenged with unmodified B16 cells. Challenge tumor growth was reduced by 56% for the IL-2/tk/adv/GCV treatment (p = 0.041) and by 77% for the GM-CSF/IL-2/tk/adv/GCV treatment p (p = 0.037), in comparison with the beta-gal/tk/GCV control group. These data may hold significant promise for the development of effective ex vivo and in vivo gene therapy modalities to counter the highly metastatic nature of human melanoma.

Environmental factors can confound identification of a major gene effect: results from a segregation analysis of a simulated population of lung cancer families.

Proper control of environmental factors can be crucial to the identification of genes that influence susceptibility to a complex trait, especially for a trait such as lung cancer, for which the environmental factor (smoking) accounts for a significant etiologic fraction of the disease. An earlier segregation analysis of 337 Louisiana families, which incorporated direct measure of tobacco consumption, provided evidence for autosomal codominant inheritance of a major gene that influenced age at onset of lung cancer. Subsequent analyses were performed in which the families were stratified into two subsets based on birth cohort of the proband; results suggested the presence of heterogeneity that were postulated to reflect the influence of cohort trends in tobacco consumption. To evaluate this hypothesis further, we simulated a population of three-generation pedigrees in which an autosomal dominant mode of susceptibility to lung cancer was transmitted, but tobacco use varied across generations corresponding to published trends in smoking. A total of 200,000 individuals in families of various sizes, ages, and cigarette smoking habits were simulated from 1900 to 1980. From this population, 324 families (2,405 individuals) with 380 cases of lung cancer were ascertained through 328 lung cancer probands. Complex segregation analysis was performed using the REGTL program of S.A.G.E. in which pack-years of tobacco exposure were incorporated directly into the likelihood calculations. Although the no major gene, environmental, and Mendelian recessive hypotheses were rejected, both dominant and codominant transmission provided a good fit to the data. Thus in a population of simulated families with autosomal dominant susceptibility to lung cancer, intergenerational differences in tobacco consumption led to the detection of autosomal codominant transmission as an acceptable hypothesis. These results underscore the potential danger of segregation analysis of complex traits in which exposure to known environmental influences may differ across generations.

Association of autoimmune thyroid disease with a microsatellite marker for the thyrotropin receptor gene and CTLA-4 in a Japanese population.

To examine the genetic contribution of the thyroid-stimulating hormone receptor (TSHR, or thyrotropin receptor) gene to autoimmune thyroid disease (AITD), we identified a dinucleotide repeat polymorphism near the TSHR gene that mapped to an 8.6 cM interval between D14S74 and D14S55 on the long arm of human chromosome 14. Association studies revealed a significant difference (p = 3.8 x 10(-5) between the TSHR microsatellite allele frequency distribution in 81 unrelated Japanese AITD patients and 113 Japanese controls, with a significant increase in the 180 pb allele (allele 1) of the microsatellite sequence (p = 5.8 x 10(-7). The risk for AITD with the 180 bp allele was 3.5, with association highly significant in female patients (p = 1.1 x 10(-5) and less dramatic, but still significant, in male patients (p = .02). These results suggest that the 180 bp allele of the TSHR microsatellite is associated with a susceptibility locus for AITD in Japanese patients. Two additional genetic markers have been evaluated for association in the Japanese AITD patients. The TSHR codon 52 (C52-->A52) transition mutation was not observed in the Japanese. A polymorphism for the CTLA-4 gene was genotyped and, while association with AITD was not observed (p = .15), a significant association was observed between CTLA-4 alleles of 110 bp (p = .01) and 106 bp (p = .004) and susceptibility to primary hypothyroidism or idiopathic myxedema, respectively.

Genetic analysis of mammographic breast density in adult women: evidence of a gene effect.

BACKGROUND: The appearance of the female breast viewed by mammography varies considerably from one individual to another because of underlying differences in the relative proportions of fat, connective tissue, and glandular epithelium that combine to create a characteristic pattern of breast density. An association between mammographic patterns and family history of breast cancer has previously been reported. However, this association has not been found in all studies, and few data are available on possible genetic components contributing to mammographic breast density. PURPOSE: Our purpose was to estimate familial correlations and perform complex genetic segregation analyses to test the hypothesis that the transmission of a major gene influences mammographic breast density. METHODS: As part of a cohort study (initiated in 1944) of families with a history of breast cancer, the probands' female relatives who were older than 40 years were asked to obtain a routine mammogram. The mammograms of 1370 women from 258 independent families were analyzed. The fraction of the breast volume occupied by radiographically dense tissue was estimated visually from video displays of left or right mediolateral oblique views by one radiologist experienced in mammography who had no knowledge of individual relationships to the probands. Data on breast cancer risk factors were obtained through telephone interviews and mailed questionnaires. Unadjusted and adjusted familial correlations in breast density were calculated, and complex genetic segregation analyses were performed. RESULTS: Sister-sister correlations in breast density (unadjusted and adjusted for age and either body mass index, menopausal status, hormone replacement therapy, waist-to-hip ratio, number of live births, alcohol consumption, or cigarette smoking status) were all statistically significant (r = .16-.27; all P<.05 [two-sided]). Estimated mother-daughter correlations were smaller in magnitude (r = .01-.17) and not statistically significant. Segregation analyses indicate that a major autosomal gene influences breast density. The mendelian transmission of a dominant gene provided the best fit to the data; however, hypotheses involving the inheritance of either a recessive gene or a codominant gene could not be ruled out. The mendelian dominant hypothesis, accounting for 29% of the variability in breast density, suggests that approximately 12% of the population would be expected to carry at least one variant allele of this putative gene. Women who inherit the variant allele would have a mean breast density about twice that of the rest of the population. CONCLUSIONS: Our preliminary findings suggest that, in this cohort of women at risk of breast cancer, mammographic breast density may be genetically influenced.

Genetic linkage analysis of growth factor loci and end-stage renal disease in African Americans.

Hypertension, diabetes mellitus and chronic glomerular diseases reportedly cause in excess of 80% of the incident cases of end-stage renal disease (ESRD) in the U.S. The factors that initiate progressive renal failure in patients with these disorders remain unknown. Several investigators have reported enhanced synthesis and activity of cytokines in the kidneys of patients with renal failure. The ensuing inflammation and fibrosis have been postulated to contribute to the development of progressive renal failure. There is also abundant evidence supporting the contribution of genetic factors in ESRD susceptibility based upon the strong familial clustering of ESRD, particularly in African Americans. Therefore, genetic linkage analysis may be useful to evaluate the role of candidate genes in several cytokine cascades that could contribute to the pathogenesis of chronic renal failure. We tested for genetic linkage between eight cytokine candidate genes and chronic renal failure in a collection of African American sibling pairs concordant for ESRD. Epidermal growth factor (EGF), platelet-derived growth factor (PDGF), transforming growth factor (TGF) beta 1, TGF-beta 2 and TGF-beta 3, and tumor necrosis factor (TNF)-alpha and TNF-beta candidate genes were selected for analysis due to their putative roles in diabetic renal disease and chronic glomerulonephritis. The interleukin-1 receptor antagonist gene (IL1RN) was also genotyped due to its reported association with diabetic nephropathy. Non-parametric (genetic model independent) affected sib pair linkage analysis was used to evaluate evidence for linkage. In order to genotype TGF-beta 3, we identified four closely linked, previously unidentified, highly polymorphic microsatellite loci near the TGF-beta 3 gene. Linkage of ESRD and transforming growth factor beta 2 polymorphisms on human chromosome 1 approached significance for non-diabetic nephropathy (predominantly chronic glomerular disease, hypertensive nephrosclerosis and unknown etiology) (P = 0.08), but showed no linkage to diabetic nephropathy. The other candidate loci did not demonstrate linkage to ESRD in the total population or in the subgroups with diabetic or non-diabetic etiologies of ESRD. The IL1RN gene did not show significant evidence for linkage to ESRD; however, we did confirm an association between allele 2 of IL1RN and ESRD (as reported in diabetic nephropathy). Overall, these results suggest that these growth factor loci do not make major contributions to the pathogenesis of ESRD in African Americans.

Association of Stein-Leventhal syndrome with the incidence of postmenopausal breast carcinoma in a large prospective study of women in Iowa.

BACKGROUND: The Stein-Leventhal syndrome (SLS), first described in 1935, is characterized by infertility, hyperandrogenization, and obesity. Because this phenotype represents an aggregation of risk factors for postmenopausal breast carcinoma, and because in general, a hormonal imbalance underlies the disorder, the authors examined the association between self-reported SLS and breast carcinoma incidence in a cohort of 34,835 cancer-free women assembled in 1986 and followed through 1992. METHODS: All participants were between the ages of 55 and 69 and held a valid Iowa driver's license. A total of 472 women in the cohort (1.35%) reported a history of SLS at baseline. Incident cases of breast carcinoma were identified annually using the State Health Registry of Iowa. Data were analyzed using Cox proportional hazards regression. RESULTS: During the follow-up period, there were 883 incident breast carcinomas, 14 among women reporting a history of SLS. Women with SLS were more likely than women without SLS to report fertility problems and menstrual irregularities, but there were no significant differences observed regarding body mass index (BMI). Although women with SLS were 1.8 times as likely to report benign breast disease than women without SLS (P < 0.01), they were not more likely to develop breast carcinoma (relative risk [RR] = 1.2; 95% confidence interval [CI] = 0.7-2). Adjustment for age at menarche, age at menopause, parity, oral contraceptive use, BMI, waist-to-hip ratio, and family history of breast carcinoma lowered the RR to 1 (95% CI = 0.6-1.9. CONCLUSIONS: Despite the high risk profiles of some women with SLS, these results do not suggest that the syndrome per se is associated with an increased risk of postmenopausal breast carcinoma.