Biomedical subjects

R R Fabsitz

Publications and source records attributed to R R Fabsitz.

At least 55 records · Page 3Linked to original sources

PubMed1996

Apolipoprotein E polymorphism in American Indians and its relation to plasma lipoproteins and diabetes. The Strong Heart Study.

Apo E is an important genetic factor in the development of cardiovascular disease, which is the leading cause of death among American Indians. We investigated the occurrence of the apo E alleles and the relation between apo E polymorphism and blood lipoproteins and apoproteins in members of 13 American Indian communities in three geographic areas. The frequencies of the epsilon 2 alleles in American Indians are significantly lower than those in white Americans, with the lowest frequencies of epsilon 2 in American Indians who reside in Arizona. Levels of LDL cholesterol and apo B were highest in those with epsilon 4 and lowest in those with epsilon 2. Concentrations of HDL cholesterol and apo A-I, however, tended to be lowest in epsilon 4 and highest in epsilon 2. Concentrations of total and VLDL triglycerides were lowest in the epsilon 3 group and higher in groups epsilon 2 and epsilon 4. Differences in concentrations of LDL cholesterol, HDL cholesterol, apo B, and apo A-I with apo E polymorphism were greater in women than in men, and differences in total and VLDL triglyceride concentrations by apo E phenotype were greater in men. Relations of total and VLDL triglycerides with apo E phenotype were stronger in women after menopause. In addition, differences in nearly all lipid and apoprotein concentrations between postmenopausal women and premenopausal women were greater if they had epsilon 2. Relations between apo E phenotype and lipoproteins were seen in individuals with diabetes mellitus as well as in nondiabetics. Apo E was significantly related to glucose control in diabetic women; those with epsilon 3 had higher glucose and hemoglobin A1C concentrations. Our findings show that (1) American Indians have low frequencies of apo epsilon 2; (2) apo E phenotype can influence levels of VLDL, LDL, HDL, apo B, and apo A-I; (3) the associations of apo E polymorphisms with lipid parameters differ between men and women; and (4) the associations in women of apo E polymorphisms with lipid parameters are modified by menopausal status.

Aged↗

PubMed1996

Hypertension in adult American Indians. The Strong Heart Study.

Hypertension is a primary risk factor for cardiovascular disease in the United States. Although cardiovascular disease is the leading cause of death among American Indians, the prevalence of hypertension, its awareness and control, and its association with other cardiovascular disease risk factors and physiological variables have not been well studied in this population. The Strong Heart Study is a longitudinal study of cardiovascular disease and its risk factors in American Indians. Participants (2703 women and 1846 men) were members of 13 tribes in central Arizona, southwestern Oklahoma, and regions of South and North Dakota. At least 1500 individuals between 45 and 74 years of age participated from each center in a baseline clinical examination conducted between July 1989 and January 1992. The examination consisted of a personal interview and physical examination that included an oral glucose tolerance test and three consecutive blood pressure measurements. This study reports data from the baseline examination on the prevalence of hypertension and correlates of blood pressure. Results indicated that despite the high frequency of diabetes and obesity, prevalence rates of hypertension in Arizona and Oklahoma were similar to those in the US population in the Third National Health and Nutrition Examination Survey (NHANES III), and rates among South/North Dakota participants were significantly lower (P < .0001). Blood pressure was higher in individuals with diabetes (P < .0001) and was significantly correlated with age (P < .0001) and albuminuria (P < .0001) but only weakly related to obesity. There was no independent relation between blood pressure and insulin. Blood pressure seems to be less affected by obesity and hyperinsulinemia in American Indians compared with other populations. Nevertheless, hypertension should be aggressively treated and controlled in American Indians because it is a known precursor to morbidity and mortality associated with diabetes and cardiovascular disease.

Aged↗

PubMed1996

Diabetes and coronary heart disease in American Indians: The Strong Heart Study.

Coronary heart disease (CHD) is the leading cause of death among American Indians. However, information on the prevalence of CHD and its association with known risk factors is limited. The purpose of the Strong Heart Study is to quantify CHD and its risk factors among three geographically diverse groups of American Indians. The population consists of 4,549 adults between 45 and 74 years of age in 13 Indian communities in Arizona, Oklahoma, and South and North Dakota. The phase I examination (1989-1991) revealed very high prevalence rates of diabetes that ranged from 33 to 72% in men and women in the three centers. Prevalence rates of definite myocardial infarction (MI) and definite CHD were higher in men than in women in all three centers (P < 0.0001) and in those with diabetes (P = 0.002 and P = 0.0003 in women and men respectively). Diabetes was associated with a relatively greater increase in prevalence of MI (prevalence rate = 3.8 vs. 1.9) and CHD (prevalence rate = 4.6 vs. 1.8) in women than in men. Logistic regression analysis indicated that the prevalence of CHD among American Indians was significantly related to age, diabetes, hypertension, albuminuria, percentage of body fat, smoking, high concentrations of plasma insulin, and low concentrations of HDL cholesterol. Lower prevalence rates of CHD were found in Arizona despite higher rates of diabetes, obesity, hypertension, and albuminuria; these lower rates may be in part related to lower smoking frequency and lower concentrations of total and LDL cholesterol. These findings from the baseline Strong Heart Study examination emphasize the relative importance of diabetes and its associated variables as risk factors for CHD among American Indian populations.

Adult↗

PubMed1995

Coronary heart disease prevalence and its relation to risk factors in American Indians. The Strong Heart Study.

Although coronary heart disease (CHD) is currently the leading cause of death among American Indians, information on the prevalence of CHD and its association with known cardiovascular risk factors is limited. The Strong Heart Study was initiated in 1988 to quantify cardiovascular disease and its risk factors among three geographically diverse groups of American Indians. Members of 13 Indian communities in Arizona, Oklahoma, and South and North Dakota between 45 and 74 years of age underwent a physical examination that included medical history; an electrocardiogram; anthropometric and blood pressure measurements; an oral glucose tolerance test; and measurements of fasting plasma lipoproteins, fibrinogen, insulin, hemoglobin A1c, and urinary albumin. Prevalence rates of definite myocardial infarction and definite CHD were higher in men than in women at all three centers (p < 0.0001) and higher in those with diabetes mellitus (p = 0.002 in men and p = 0.0003 in women). Diabetes was associated with relatively higher prevalence rates of myocardial infarction (diabetic:nondiabetic prevalence ratio = 3.8 vs. 1.9) and CHD (prevalence ratio = 4.6 vs. 1.8) in women than in men. Prevalence rates of heart disease were lowest in the communities in Arizona; prevalence rates were similar in Oklahoma and South Dakota/North Dakota and were two- to threefold higher than those in Arizona. By logistic regression, prevalent CHD among American Indians was significantly and independently related to age, diabetes, hypertension, albuminuria, percentage of body fat, smoking, high concentrations of plasma insulin, and low concentrations of high density lipoprotein cholesterol. In contrast to reports from other non-Indian populations, diabetes was the strongest risk factor. The lower prevalence of CHD among Indians in Arizona is distinctive in view of their higher rates of diabetes, obesity, hypertension, and albuminuria, but it may be partly related to their low frequency of smoking and their low concentrations of total and low density lipoprotein cholesterol. These findings from the initial Strong Heart Study examination emphasize the importance of diabetes and its associated variables as risk factors for CHD in Native American populations.

Aged↗

PubMed1995

Cardiovascular disease risk factors among American Indians. The Strong Heart Study.

The Strong Heart Study, a study of cardiovascular disease among American Indians, was conducted to determine cardiovascular disease rates and the prevalence of risk factors among members of 13 tribal groups in South Dakota/North Dakota (SD/ND), southeastern Oklahoma, and Arizona. From 1989 to 1992, 4,549 tribal members aged 45-74 years (62% of eligible participants) were surveyed and examined for cardiovascular disease and its risk factors. Mean total cholesterol concentrations were over 20 mg/dl lower among the men and 27 mg/dl lower among the women than national mean levels for the same age groups. Cholesterol levels varied by tribal group; Arizona Indians had mean levels more than 20 mg/dl lower than those of SD/ND Indians. The prevalence of hypercholesterolemia was almost twice as high among SD/ND Indians as among Arizona Indians, but the rates for all three groups were much lower than total US rates (all races). Mean levels of high density lipoprotein cholesterol were lower among Indian men and women than in the US population as a whole. The prevalence of hypertension among Arizona and Oklahoma Indians was higher than that for the entire United States. SD/ND Indians had significantly lower mean blood pressures and prevalence rates of hypertension than Oklahoma and Arizona Indians and the United States as a whole. The prevalence of cigarette smoking was higher for all Indian groups except Arizona women in comparison with US rates. Smoking rates were highest in SD/ND and lowest in Arizona. Indian smokers smoked fewer cigarettes per day than the average US smoker. Arizona Indians had the highest prevalence of diabetes mellitus; over 60% of those participants were diabetic. In Oklahoma and SD/ND, one third of the men and over 40% of the women were diabetic. In addition, 13-20% of the participants had impaired glucose tolerance. Proteinuria was also a common problem; almost half of the Arizona Indians had micro- or macroalbuminuria, and 20% of Oklahoma and SD/ND Indians had significant proteinuria. The prevalence of obesity was high in all three groups, with Arizona Indians having the highest rates and the highest mean body mass indices. The prevalence of current alcohol use was lower among Indians than in the nation as a whole, but binge drinking was common among those who used alcohol. These results indicate that cardiovascular disease risk factors vary significantly among tribal groups. Prevention programs tailored toward decreasing the prevalence of risk factors are recommended for long-term reduction of cardiovascular disease rates in American Indian communities.

Aged↗

PubMed1995

Diabetes and impaired glucose tolerance in three American Indian populations aged 45-74 years. The Strong Heart Study.

OBJECTIVE: To estimate prevalence rates of diabetes and impaired glucose tolerance (IGT) in three American Indian populations, using standardized diagnostic criteria, and to assess the association of diabetes with the following selected possible risk factors: age, obesity, family history of diabetes, and amount of Indian ancestry. RESEARCH DESIGN AND METHODS: This cross-sectional study involved enrolled members, men and women aged 45-74 years, of 13 American Indian tribes or communities in Arizona, Oklahoma, and South and North Dakota. Eligible participants were invited to the clinic for a personal interview and a physical examination. Diabetes and IGT status were defined by the World Health Organization criteria and were based on fasting plasma glucose and oral glucose tolerance test results. Data on age, family history of diabetes, and amount of Indian ancestry were obtained from the personal interview, and measures of obesity included body mass index, percentage body fat, and waist-to-hip ratio. RESULTS: A total of 4,549 eligible participants were examined, and diabetes status was determined for 4,304 (1,446 in Arizona, 1,449 in Oklahoma, and 1,409 in the Dakotas). In all three centers, diabetes was more prevalent in women than in men. Arizona had the highest age-adjusted rates of diabetes: 65% in men and 72% in women. Diabetes rates in Oklahoma (38% in men and 42% in women) and South and North Dakota (33% in men and 40% in women), although considerably lower than in Arizona, were several times higher than those reported for the U.S. population. Rates of IGT among the three populations (14-17%) were similar to those in the U.S. population. Diabetes rates were positively associated with age, level of obesity, amount of Indian ancestry, and parental diabetes status. CONCLUSIONS: Diabetes is found in epidemic proportions in Native American populations. Prevention programs and periodic screening should be implemented among American Indians. Standards of care and intervention have been developed by the Indian Health Service for individuals in whom diabetes is diagnosed. These programs should be expanded to include those with IGT to improve glycemic control or to reduce the risk of development of diabetes as well as to reduce the risk of diabetic complications.

Age Factors↗

PubMed1994

Genetic influences on adult weight gain and maximum body mass index in male twins.

The National Heart, Lung, and Blood Institute Twin Study is a multicenter, longitudinal study of 514 white, male twin pairs examined during military induction at the mean age of 20 years (1943) and by the National Heart, Lung, and Blood Institute Twin Study at mean ages 48 (1971), 58 (1981), and 63 years (1986). Of these, 121 of 254 monozygotic pairs and 113 of 260 dizygotic pairs had complete data for all examinations. Using these data, genetic influences on maximum body mass index (BMI) and changes in BMI during this 43-year interval were estimated. BMI (kg/m2) was calculated for each examination and for the maximum weight as recalled by the participant at the last examination. Regression equations were fitted to each person's four-examination measurements to estimate the trend in weight change over adulthood. Twins gained an average of 0.11 kg/m2 per year from mean ages 20-63 years. Maximum BMI averaged 28.4 kg/m2 for monozygotic twins and 28.3 kg/m2 for dizygotic twins. The distribution of the ages at maximum BMI appeared to be bimodal for each zygosity, with modes around ages 20 and 60 years. Heritability (variation attributable to genetic factors) was estimated to be 0.71 (95% confidence interval 0.55-0.87) for maximum BMI and 0.70 (95% confidence interval 0.55-0.84) for trend in adult weight gain. In contrast, variability of BMI around the trend line showed no evidence of significant genetic determination.

Adolescent↗

PubMed1994

Genetic influences on age-related change in total cholesterol, low density lipoprotein-cholesterol, and triglyceride levels: longitudinal apolipoprotein E genotype effects.

This study addressed the possible influence of apolipoprotein E (apo E) genotype on age-related changes in total cholesterol (TC), low density lipoprotein-cholesterol (LDL-C), and triglyceride (TG) levels in older males. Apo E is a component of LDL, is a ligand for the LDL receptor, and apo E genotype has been consistently associated with variation in mean levels of TC and LDL-C, and also appears to influence TG levels. Using male twins followed longitudinally between mean ages of 48 and 63 years, the change in TC, LDL-C, and TG over time for individuals with the epsilon 3 epsilon 3 and the epsilon 3 epsilon 4 genotypes was contrasted. At exam 1 mean TC and LDL-C levels were lower in the epsilon 3 epsilon 3 group than in the epsilon 3 epsilon 4 group, but at exam 3 mean TC and LDL-C levels were significantly higher in the epsilon 3 epsilon 3 group than in the epsilon 3 epsilon 4 group. The rate of change in TC and LDL-C with age differed significantly between epsilon 3 epsilon 3 and epsilon 3 epsilon 4 groups. Results for TG were not statistically significantly. These findings suggest that the apo E genotype effects on risk of coronary artery disease may be age-dependent. This study demonstrates the value of longitudinal studies in refining models for genetic risk factors for disease.

Adult↗

PubMed1994

16-year incidence of ischemic heart disease in the NHLBI twin study. A classification of subjects into high- and low-risk groups.

Prospective data from the National Heart, Lung, and Blood Institute (NHLBI) Twin Study were used to investigate the relationship of risk factors measured in 1970 to 1971 to 16-year incidence of ischemic heart disease (IHD) in 905 males born between 1917 and 1927. A newly developed methodology, tree-structured survival analysis (TSSA), was used to classify subjects into discrete subgroups that differed significantly in profiles of risk factors and incidence of IHD. On the basis of five characteristics--systolic blood pressure (SBP), high-density-lipoprotein cholesterol (HDL-C), 1-hour postload glucose levels, forced expiratory volume in 1 second (FEV1), and a family history score for heart disease--the TSSA algorithm partitioned the cohort into six discrete subgroups that formed three clusters of individuals with distinct IHD experience. Highest IHD incidence rates were experienced by a subgroup of 56 men with baseline SBP above 134 mm Hg and HDL-C levels lower than 33 mg/dL. No IHD events were observed in a subgroup of 117 men who had low SBP, high FEV1, and a negative family history of heart disease. Relationships to the twinning condition showed that for both zygosities, cotwin-pair members were in the same risk subgroup more often than expected; however, the overall difference between the frequency of monozygotic (MZ) and dizygotic (DZ) cotwins was relatively small. The highest MZ/DZ ratios of observed to expected cotwin-pair membership occurred in subgroups with the highest and lowest incidences of IHD, suggesting that these extremes of incidence are most likely to be genetically determined.

Aged↗

PubMed1994

Minimal genetic influences on plasma fibrinogen level in adult males in the NHLBI twin study.

Plasma fibrinogen was determined in 189 twins participating at the Indiana center during the third examination of the NHLBI twin study with a mean age of 63 years. Moderate heritability estimates were obtained from 44 complete MZ pairs and 39 complete DZ pairs. After adjustment of fibrinogen levels for age and other confounding variables related to cardiovascular disease risk, the maximum likelihood heritability estimate was only 30% (p = 0.03). Plasma fibrinogen was most strongly associated with smoking and the presence of diabetes. Omitting all subjects with diabetes or cardiovascular disease further reduced the heritability estimates slightly, and most path models including genetic parameters provided no significant improvement in fit over a model determined solely by random environmental effects. Our results are consistent with the environment rather than genetic influences having a greater influence on the level of plasma fibrinogen.

Aged↗

PubMed1994

Correlations of alcohol consumption with related covariates and heritability estimates in older adult males over a 14- to 18-year period: the NHLBI Twin Study.

Consistent maximum-likelihood heritability estimates of consumption of alcoholic beverages were observed at three separate times during a 14- to 18-year period in adult twin males initially aged 42-56 years in 1969-1973. Log transformation of the average number of drinks/week of the returnees to all three examinations was examined relative to potential covariates representing both antecedents of drinking alcohol and consequences of alcohol consumption. Significant relationships were noted for 38 of the covariates at one or more of the separate examinations, including positive correlations with smoking, coffee consumption, high-density lipoprotein cholesterol, mean corpuscular volume, systolic blood pressure, uric acid and behavioral measures, and negative correlations with blood urea nitrogen, red blood cell count, tea consumption, and tricep skinfolds. Analysis of the average alcohol consumption adjusted for nine independent covariates selected from multiple stepwise regression resulted in a modest decline in maximum-likelihood heritability estimates compared with unadjusted data, but little difference from heritability estimates obtained when abstainers from alcohol (no alcoholic beverages consumed at all three examinations) were excluded. The most striking effect of omitting abstainers from alcohol was the decline in the intraclass correlations in dizygotic twins. Bivariate analyses of alcohol and individual covariates revealed the phenotypic correlation between alcohol consumption and a measure of hostility was primarily environmental, that for high-density lipoprotein, smoking and coffee drinking with alcohol was primarily genetic, and the phenotypic correlation between alcohol consumption and mean corpuscular volume had both significant genetic and environmental correlations.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

Genetic and environmental correlations between obesity and body fat distribution in adult male twins.

Genetic and environmental correlations between measures of obesity [body mass index (BMI)] and body fat distribution [waist/hip ratio (WHR) and subscapular/triceps ratio (SSTR)] were examined in 133 monozygotic and 129 dizygotic pairs of elderly white male twins, age 59 to 70 years, participating in the third cardiovascular examination of the National Heart, Lung, and Blood Institute Twin Study. The BMI, WHR, and SSTR fat measures were significantly correlated in these twins, with BMI more closely related to WHR (r = 0.52) than to SSTR (r = 0.18), and the WHR-SSTR association intermediate (r = 0.27). Multivariate genetic analyses of the three indexes using the LISREL modeling approach indicated a significant heritable component for each fatness variable, h2 = 0.66, 0.46, and 0.25 for BMI, WHR, and SSTR, respectively, and a significant correlation between genetic influences on BMI and WHR (genetic r = 0.51). The common genetic component accounted for 54% of the observed BMI-WHR correlation, suggesting that overall obesity and abdominal adiposity distribution are mediated to some extent by similar genetic influences. The genetic correlations between SSTR and BMI and between SSTR and WHR were not significantly different from zero, suggesting that genetic influences on skinfold distribution are independent of those on abdominal body fat and overall obesity. The genetic findings support the hypothesis that the WHR and SSTR indexes do not assess the same dimensions of fat patterning.

Adipose Tissue↗

PubMed1993

The NHLBI male veteran twin study data.

The National Heart, Lung and Blood Institute (NHLBI) twin study is a collaborative, longitudinal study of the role of genetic risk factors on subsequent cardiovascular disease processes in 514 pairs of white, male World War II and Korean veteran twins born between 1917 and 1927. This paper describes the sampling procedures and zygosity determination at the initial examination, participation by the cohort members at later examinations, and a summary of the variables provided for Genetic Analysis Workshop 8 (GAW8).

Aged↗

PubMed1992

Decline in cognitive performance in aging twins. Heritability and biobehavioral predictors from the National Heart, Lung, and Blood Institute Twin Study.

The present study examined the contribution of genetic factors to Digit Symbol performance and its decline in 23 monozygotic twin pairs (mean age at examination 1, 57.1 years) and 21 dizygotic twin pairs (mean age at examination 1, 56.3 years). These men were assessed twice during a 5-year interval as part of the National Heart, Lung, and Blood Institute Twin Study. The prevalence of decline (a change, greater than 1 SD) during the 5-year interval was 35% and 39% for monozygotic and dizygotic twins, respectively. The pairwise concordance for decline was 45% in monozygotic and 8% in dizygotic twin pairs, suggesting a possible role for genetic factors in the decline in Digit Symbol performance in this sample. A comparison of baseline biologic and behavioral characteristics within monozygotic twin pairs discordant for decline in Digit Symbol performance revealed that decliners had higher initial systolic blood pressures, lower serum cholesterol levels, and lower heart rates than nondecliners.

Aged↗

PubMed1992

Risk factors for coronary heart disease in diabetic and nondiabetic Native Americans. The Strong Heart Study.

The Strong Heart Study is a study of cardiovascular disease and its risk factors among diabetic and nondiabetic Native Americans. The study includes 12 tribes in Arizona, Oklahoma, and North and South Dakota. Phase I, initiated in October 1988, included a mortality survey to determine CVD death rates in individuals 35-74 yr old between 1984 and 1988, and a medical record review to determine rates of myocardial infarction and stroke for individuals ages 45-74 during the same time. In addition, a physical examination was performed on persons 45-74 yr old to measure the prevalence of cardiovascular and peripheral vascular diseases and known and suspected risk factors. In Phase II, CVD mortality and morbidity rates will be determined in the examined cohort by surveillance. CVD risk factors, changes in risk factors over time, and the relationship between risk factors and CVD incidence will be assessed longitudinally. This study provides data on the relative importance of cardiovascular risk factors in nondiabetic and diabetic Native Americans and will provide insight into possible variations in the quantitative or qualitative importance of CVD risk factors among diverse population groups.

Adult↗

PubMed1992

Evidence for independent genetic influences on obesity in middle age.

The National Heart, Lung, and Blood Institute (NHLBI) Twin Study provided longitudinal data on a cohort of 514 pairs of adult male twin pairs who were examined at approximate ages of 48, 57, and 63 years. Because the sample was selected from military veterans, height and weight data were also available from their induction physical examinations when they were approximately 20 years of age. From the total NHLBI Twin Study cohort, 124 monozygotic and 119 dizygotic male twin pairs had complete data available for both members of the pair at induction and three examinations spanning 43 years of adult life. Using these data, the contributions of genetics and shared and non-shared environmental factors to BMI over the 43 year period were estimated by model fitting procedures. Model fitting included both a factor decomposition of these effects as well as a developmental path model. Results from the decomposition procedure indicate significant genetic effects at each examination cycle. Fitting a developmental path model, two independent genetic contributions to the variability of BMI were found: one at, or prior to, the induction examination about age 20, and a second between ages 20 and 48. Significant non-shared environmental contributions at each examination were also indicated, but shared environmental effects were not significant. We conclude that cumulative genetic effects explain most of the tracking in obesity over time; non-shared environmental effects, although significant at each age, are relatively short-lived and make only a minor contribution to tracking.

Adult↗

PubMed1991

Concordance for dyslipidemic hypertension in male twins.

Sixty cases of dyslipidemic hypertension were identified in the 1028 middle-aged, white, male twin participants in the first examination of the National Heart, Lung, and Blood Institute Twin Study (1969 to 1973). The prevalence of dyslipidemic hypertension was similar by zygosity but proband concordance was three times greater in monozygotic than dizygotic twins (0.44 [seven concordant and 18 discordant pairs] vs 0.14 [two concordant and 24 discordant pairs]), suggesting a genetic effect on the condition. Low high-density lipoprotein cholesterol level was the most common lipid abnormality in concordant pairs. Mortality from ischemic heart disease was significantly higher in individuals with dyslipidemic hypertension. Obesity and glucose intolerance were closely associated with the syndrome. Moreover, within the 18 discordant monozygotic twin pairs, the twins with dyslipidemic hypertension had gained significantly more weight as adults and were significantly heavier than their unaffected cotwins. Thus, although genetic factors may influence development of dyslipidemic hypertension, nongenetic, potentially modifiable aspects of obesity are also closely related to expression of this clinically important syndrome.

Adult↗

PubMed1991

Effects of selective return on estimates of heritability for body mass index in the National Heart, Lung, and Blood Institute Twin Study.

In the National Heart, Lung, and Blood Institute Twin Study, body mass index (BMI) was studied at military induction and at three subsequent examinations spanning five decades in a cohort of white, male World War II veterans. At military induction (1940s) and again at the first clinical examination of this study (1969-1973), there was close agreement of three commonly used estimates of heritability (range 0.72 to 0.80), and no evidence of a difference in total variance of BMI between the zygosities. However, at the last two examinations (1980s), the total variance in dizygotic (DZ) twins was significantly greater than that of monozygotic (MZ) twins (P less than 0.01) and these same heritability estimates varied widely. The among-pair estimate of heritability fell to unrealistic negative values, the within-pair estimate rose to values of 1.0 or greater, and the intraclass correlation coefficient estimate was slightly lower than in the entire cohort at baseline. The cause of the unequal zygosity total variance appears to have been nonparticipation at later examinations of MZ twins with extreme values of BMI, with no evidence of a similar selection process influencing DZ twins. This selection process biased the three estimates of heritability, making it difficult to determine which estimate is the most appropriate. Despite these biases, it remains clear that genetic factors contribute substantially to BMI in this population.

Adult↗