Genome-wide search for genes related to the fat-free body mass in the Québec family study

Fat-free mass (FFM) consists mostly of skeletal muscle and bone tissues, and identification of the genes and molecular mechanisms involved in the control of FFM would have implications for the understanding of sarcopenia and potentially osteoporesis associated with aging, as well as the response to starvation, refeeding, anorexia, and any other conditions in which lean body mass is important. A genome-wide search for genes related to body leanness has been completed in the Quebec Family Study (QFS). Microsatellite markers (N = 292) from the 22 autosomal chromosomes were typed. The mean spacing of the markers was 11.9 centimorgans (cM) (range, <0.1 to 41). FFM was calculated from percent body fat, derived from underwater weighing, and body weight and was adjusted by regression for age and sex effects before analysis. A maximum of 336 sib pairs or 609 pairs of extended relatives were analyzed using single-point Haseman-Elston regression (SIBPAL and RELPAL) and multipoint variance component (SEGPATH) linkage analyses. Significant linkages were observed on chromosomes 15q25-q26 for a CA repeat within the insulin-like growth factor 1 receptor (IGF1R) gene (Lod score = 3.56) and at 18q12 with D18S877 (Lod score = 3.53) and D18S535 (Lod score = 3.58), 2 markers located 10 cM apart. A moderately significant linkage was also observed on chromosome 7p15.3 with the marker D7S1808 (Lod score = 2.72). The most obvious candidate genes within the regions identified by these linkages include the IGF1R on 15q and neuropeptide Y (NPY) and growth hormone-releasing hormone (GHRH) receptor on 7p. On 18q, the melanocortin receptor 4 (MC4R) is not likely the candidate gene for the observed linkage. This study represents the first genome-wide search for genes that may be involved in the regulation of the lean component of body mass in humans.

A tale of two bounties: the impact of competing fees on physician behavior

This study examines how the volume of privately insured services provided in hospital inpatient and outpatient departments changes in response to reductions in Medicare physician payments. We hypothesize that physicians consider relative payment rates when choosing which patients to treat in their practices. When Medicare reduces its payments for surgical procedures, as it did in the late 1980s, physicians are predicted to treat more privately insured patients because they become more lucrative. We use data from 182 hospitals for seventeen major procedures groups, covering a forty-five-month period between 1988 and 1991 that encom passes a twenty-four-month period before the reduction in Medicare fees and twenty-one months after the reduction. Our findings are consistent with the predictions for a number of procedure groups, but not for all of them. One implication of the findings is that societal savings from Medicare fee reductions are overstated if one does not also consider spillover effects in the private insurance market.

Reproducibility of maximal exercise test data in the HERITAGE family study

PURPOSE

The reproducibility of responses to maximal cycle ergometer testing was determined using data from the HERITAGE Family study at four Clinical Centers in the United States and Canada.

METHODS

Reproducibility was determined from maximal exercise test data obtained a) on 2 d in a sample of 390 subjects (198 men and 192 women), b) across 4 d in an Intracenter Quality Control (ICQC) substudy with 55 subjects who were not part of the main study, and c) across 2 wk in a Traveling Crew Quality Control (TCQC) substudy with the same eight subjects who were tested at each of the four centers. Reproducibility was evaluated using technical errors, coefficients of variation (CV) for repeated measures, and intraclass correlation coefficients (ICC) for selected variables obtained on the main cohort, as well as on the ICQC and TCQC substudies.

RESULTS

With the exception of systolic and diastolic blood pressures and respiratory exchange ratio, all the other variables (heart rate, ventilation, VO2, and VCO2) were highly reproducible, with CV below 10% and ICC over 0.86. These results were similar to those previously reported on the same subjects at a submaximal power output associated with 60% VO2max. Results were consistent for the main cohort, the ICQC sample, the TCQC sample, and across all four Clinical Centers.

CONCLUSIONS

Day-to-day variations are small and reproducibility is high for maximal values of heart rate, ventilation, VO2 and VCO2 at each of the four Clinical Centers of the HERITAGE Family Study.

Supplemental health insurance for Medicare beneficiaries

Because Medicare leaves beneficiaries at risk for significant health care costs, most need to obtain some form of supplemental coverage to protect themselves against the financial burden of illnesses. Close to nine out of ten Medicare beneficiaries age 65 or older now have some health coverage that provides additional benefits beyond standard Medicare Part A and Part B. The most common types of supplementation are insurance coverage offered by former employers, policies that individual beneficiaries purchase, benefits offered by Medicare managed care plans and assistance provided through the Medicaid program. This supplementation is expensive--to beneficiaries, employers, states, and to the federal government. The availability and extent of financial protection offered by supplemental coverage provided by former employers and through managed care also appears to be increasingly unstable. Structural reform of the Medicare program needs to include a broad reexamination of the basic benefits package and of the potential benefits and costs of public and private supplementation of the health insurance coverage promised to beneficiaries.

Extrauterine abdominal pregnancy: report of a case

A healthy, 34-year-old, gravida 3, para 1,011, patient presented for cesarean delivery in her 35th week of gestation with a diagnosis of complete placenta previa. During her 26th week of gestation, the patient was admitted to a high-risk obstetric unit with the diagnosis of premature rupture of membranes. Numerous ultrasonographic studies were conducted throughout her 10-week hospital stay, confirming the admitting diagnosis. A routine cesarean section was planned, and preparations were made for a potential increase in blood loss related to the placenta previa. The procedure began under spinal anesthesia and, upon incision of the abdomen, an extrauterine pregnancy was identified. The patient was immediately anesthetized and intubated at the request of the surgeon. During the 3-hour surgical procedure, the patient sustained massive blood loss, transfusions, central line placement, and aggressive pharmacological therapy. The patient was extubated the day after surgery, and was discharged approximately 1 week later. The only major complication was compartment syndrome of the left upper extremity related to the infiltration of vasopressors requiring fasciotomy and closure 2 days later. The incidence, morbidity/mortality, and anesthetic implications of abdominal pregnancy are reviewed.

Total body fat and abdominal visceral fat response to exercise training in the HERITAGE Family Study: evidence for major locus but no multifactorial effects

The familial etiology of the response in total fat mass (FM) and abdominal visceral fat (AVF) to 20 weeks of exercise training was investigated in families participating in the HERITAGE Family Study. AVF (measured by computed tomographic scanning) and FM (measured by underwater weighing techniques) were assessed at baseline (in a sedentary state) and after 20 weeks of exercise training. The response AVF (AVFdelta) and response FM (FMdelta) were computed as the simple delta values (posttraining - baseline) and adjusted for the effects of sex, generation, and a polynomial in age using multiple regression analysis. To index the AVF response independently of the response in FM and the initial level of visceral fat, the AVFdelta was also adjusted for age and baseline AVF (AVFB) and FMdelta. Familial correlation analysis was used to investigate the multifactorial familial effects (polygenic and/or familial environmental), and segregation analysis was used to search for major gene effects. For the age-adjusted AVFdelta, a putative recessive locus accounting for 18% of the variance (q2 = 1%) was detected. Adjusting AVFdelta for AVFB and FMdelta slightly increased the percentage of variance accounted for (to 26%, q2 = 3%) but did not radically alter the pattern of the parameter estimates. For FMdelta, a putative dominant locus accounting for 31% of the variance (q2 = 49%) was noted. In conclusion, the results were consistent across methods in suggesting that there is little evidence of a multifactorial heritability for either AVFdelta or FMdelta. Rather, the familial etiology of the response to exercise training appears to be primarily due to putative major genes (a recessive locus for AVFdelta and a dominant locus for FMdelta). In addition, a pleiotropic/oligogenic system underlying these variables was inferred. That is, the putative loci for FMdelta and/or AVFB also may impact the AVFdelta, with an additional independent major locus effect on AVFdelta after the former influences have been removed.

Alterations in body weight and composition consequent to 20 wk of endurance training: the HERITAGE Family Study

BACKGROUND

Obesity is a major public health problem in the United States. The role of physical activity and formal exercise in controlling body weight has not been clearly determined.

OBJECTIVE

This study determined the magnitude of change in body weight and composition across sex, race, and age in response to 20 wk of endurance training.

DESIGN

Men and women (n = 557) of various ages (16-65 y) and 2 races (black and white) exercised on cycle ergometers 3 d/wk for a total of 60 exercise sessions starting at 55% of maximal oxygen consumption (VO(2)max) for 30 min/session and building to 75% of VO(2)max for 50 min/session, where it was maintained during the last 6 wk. Skinfold-thickness measurements, circumferences, body composition (by hydrostatic weighing), and body fat distribution (by computed tomography scan at L4-L5 and the waist-hip ratio) were determined before and after training.

RESULTS

All skinfold-thickness and circumference measures, waist-hip ratio, body mass index, total body mass, fat mass, percentage body fat, and computed tomography scan measures of total, subcutaneous, and visceral abdominal fat decreased with training, whereas total body density and fat-free mass increased. These changes were significant, but small. There were several differences in training response by sex and race, but not by age.

CONCLUSIONS

A short-term exercise intervention can induce favorable changes in body composition, but the magnitude of these changes is of limited biological significance. Increasing physical activity likely has a major effect on body-composition and fat distribution characteristics only when it is of a greater magnitude and sustained for much longer periods

Body fat, resting and exercise blood pressure and the angiotensinogen M235T polymorphism: the heritage family study

OBJECTIVE

The association of resting and exercise blood pressure (BP) and fat mass with the angiotensinogen (AGT) M235T polymorphism was investigated in 522 sedentary Caucasian subjects from 99 families.

RESEARCH METHODS AND PROCEDURES

Resting BP was measured on two separate days, three times each day, and the mean of six valid measurements was used. Exercise BP was measured during a cycle ergometer test at a constant power output (50 W). Body composition was derived from under-water weighing and the AGT M235T polymorphism was typed with a polymerase chain reaction-based method.

RESULTS

Neither resting nor exercise BP was associated with the AGT genotypes. In mothers, the homozygotes for the T allele showed 8.8 kg and 7.1 kg greater (p=0.017) age-adjusted body fat mass (FM) than the MM homozygotes and heterozygotes, respectively. Sixty-nine percent of all TT homozygotes were found in the highest FM tertile, whereas only 16% of the MM homozygotes fell in the same tertile (p = 0.008). Moreover, a significant interaction was seen between FM and T-allele carrier status in women with regard to resting diastolic BP (p = 0.002). Among women with a FM> or =24 kg, carriers of the T allele showed a 6.3 mmHg higher diastolic blood pressure (DBP) than non-carriers whereas no difference was found in women with a FM less than 24 kg. A similar trend toward an interaction term was evident with resting systolic blood pressure (p = 0.011) and exercise DBP (p = 0.012). Body fat was not associated with the AGT polymorphism in fathers or in offspring.

DISCUSSION

These data suggest that the AGT M235T polymorphism is associated with body fatness in women, and that the relationship between DBP and AGT M235T polymorphism is dependent on FM in middle-aged sedentary normotensive women.

Familial aggregation of VO(2max) response to exercise training: results from the HERITAGE Family Study

The aim of this study was to test the hypothesis that individual differences in the response of maximal O(2) uptake (VO(2max)) to a standardized training program are characterized by familial aggregation. A total of 481 sedentary adult Caucasians from 98 two-generation families was exercise trained for 20 wk and was tested for VO(2max) on a cycle ergometer twice before and twice after the training program. The mean increase in VO(2max) reached approximately 400 ml/min, but there was considerable heterogeneity in responsiveness, with some individuals experiencing little or no gain, whereas others gained >1.0 l/min. An ANOVA revealed that there was 2.5 times more variance between families than within families in the VO(2max) response variance. With the use of a model-fitting procedure, the most parsimonious models yielded a maximal heritability estimate of 47% for the VO(2max) response, which was adjusted for age and sex with a maternal transmission of 28% in one of the models. We conclude that the trainability of VO(2max) is highly familial and includes a significant genetic component.

Segregation analysis of regional fat distribution in families from Andhra Pradesh, India

OBJECTIVE

Segregation analysis was used to examine the major gene evidence for regional fat distribution and whether the effects of covariates such as energy variables (intake and expenditure) or total subcutaneous fat, impact on the major gene inference.

SUBJECTS

The data consist of measurements made on 1691 individuals in 432 pedigrees residing in the Chittor district of Andhra Pradesh, India, during the period from January 1989 to February 1990.

MEASUREMENTS

Fat distribution was computed as the ratio of trunk skinfold sum (subscapular + suprailiac + abdominal) to extremity skinfold sum (biceps + triceps + medial calf). The trunk/extremity skinfold ratio (TER) was also analyzed after adjusting for the amount of energy expended in various activities and energy intake (TER-E), as well as after adjusting for overall level of fatness as measured by the sum of six skinfolds (TER-SF6).

METHODS

Segregation analysis was applied using the unified model (POINTER).

RESULTS

For the TER all of the conditions needed to satisfy a major gene hypothesis were met, and a putative recessive locus in the presence of a multifactorial component was inferred. Adjusting the TER for energy intake (EI) and energy expenditure (EE) did not change these results. However, adjusting for total subcutaneous fat did alter the results. Specifically, after removing the effects due to total fat, there was a major non-Mendelian effect (free tau s) with additional multifactorial influences, and with generation heterogeneity in both components.

CONCLUSIONS

A putative major locus for fat distribution as indexed by the TER was found. However, further analyses suggested the hypothesis that this major gene may be primarily for total fat with secondary effects on fat distribution (that is, major gene pleiotropy). The possibility that there is a second locus that is modified by interactions with gender and age, and that impacts on the preferential accumulation of fat in the trunk vs extremity depots could be inferred.

Should Medicare HMO benefits be standardized?

Legislation enacted in 1990 standardized Medigap benefits but not the benefits of health maintenance organizations (HMOs) that serve Medicare beneficiaries. An examination of marketing materials in two large counties reveals the potential for enormous confusion among beneficiaries because of differences in wording to describe the same benefit, health plans' failure to list Medicare-covered services, and the differences in the benefits themselves. To date, the Health Care Financing Administration (HCFA) has not been able to overcome this confusion through the comparative material distributed on its Web site; indeed, significant errors were found, reflecting to some extent the underlying difficulties in characterizing benefits. Ways of ameliorating the situation are discussed.

Evidence of a major locus for lipoprotein lipase (LPL) activity in addition to a pleiotropic locus for both LPL and fasting insulin: results from the HERITAGE Family Study

A major gene hypothesis for heparin releasable plasma lipoprotein lipase (PH-LPL) activity was assessed using segregation analyses of data on 495 members in 98 normolipidemic sedentary families of Caucasian descent who participated in the HERITAGE Family Study. Segregation analyses were performed on PH-LPL adjusted for age, and on PH-LPL activity adjusted for age and fasting insulin. Prior to adjustment for insulin, neither a major gene effect nor a multifactorial component could be rejected, and support for a major gene was equivocal i.e. neither the Mendelian transmission nor the no transmission (equal tau s) models were rejected. However, after adjusting for the effects of insulin, a major gene effect on PH-LPL activity was unambiguous. The putative locus accounted for 60% of the total phenotypic variance, and the homozygous recessive form affected 10% (q2) of the sample (i.e. gene frequency (q) = 0.31), and led to a low PH-LPL value. The lack of a significant multifactorial effect suggested that the familial etiology of PH-LPL activity adjusted for insulin was likely to be primarily a function of the major locus. In conclusion, the present study is the first to report segregation analyses on PH-LPL activity prior to and after adjusting for insulin, and suggests that there is an indication of a pleiotropic genetic effect on PH-LPL activity and insulin, in addition to a major gene effect on PH-LPL activity alone.

Segregation analysis of body mass index in a large sample selected for obesity: the Swedish Obese Subjects study

OBJECTIVE

To investigate a major gene hypothesis for body mass index (BMI) in a large sample of probands (n = 2580, ages 37-57 years) who were selected for obesity (BMI> or =34 kg/m2 for males and > or =38 kg/m2 for females), along with their spouses and first-degree relatives (n = 11,204 family members). The probands were recruited as part of an intervention trial assessing whether mortality and morbidity were improved after surgical intervention for obesity as part of the Swedish Obese Subjects (SOS) study.

METHODS AND PROCEDURES

The current analyses were based on BMI measures obtained before intervention. Segregation analysis was carried out using the mixed model implementation in PAP (Pedigree Analysis Package), which allowed for ascertainment correction and for genotype-dependent effects of covariates (sex and age) in both the major gene component and the multifactorial (i.e., polygenic and familial environment) component.

RESULTS

Both a major effect and a multifactorial effect were significant. The percentage of the total variance accounted for by the multifactorial effect was 17%-24% (increasing as a function of age), and by the major effect, 8%-34% (decreasing as a function of age). Although tests on the transmission probabilities (taus) were not compatible with Mendelian expectations of 1, 1/2, and 0, the equal taus model was rejected (i.e., the effect is transmitted in families) and the point estimates (0.96, 0.60, and 0.17) compared favorably to Mendelian expectations. The major effect was transmitted in a codominant fashion, consistent with a gene-environment interaction.

DISCUSSION

These results suggest both multifactorial and major effect etiologies for BMI in these families of extremely obese probands. Before 20 years of age, the major effect dominates the BMI expression, but after age 20, multifactorial effects account for the most variance. Although the major effect is transmitted in these families, the pattern does not appear to be consistent with a simple Mendelian trait. The possibility of additional major loci (i.e., epistasis) and gene by environment interactions may explain these findings.

Familial aggregation of resting blood pressure and heart rate in a sedentary population: the HERITAGE Family Study. Health, Risk Factors, Exercise Training, and Genetics

The familial aggregation of resting systolic blood pressure (SBP), diastolic blood pressure (DBP), and heart rate (HR) was assessed in 98 white families, who participated in the HERITAGE Family Study, and were selected to be sedentary, and primarily nonobese and normotensive. In the present study, 522 family members were sedentary at baseline examination, and resting SBP, DBP, and HR measured during this examination were investigated. If physical activity level is a potent environmental factor, then we expected that the relative contribution of environmental factors to the familial aggregation of blood pressure (BP) would be somewhat reduced, because activity was controlled for in this study. Using a familial correlation model, maximal heritabilities were estimated to be 54%, 41%, and 32% for resting SBP, DBP, and HR, respectively, in these families; and they were 51%, 42%, and 34% for resting SBP, DBP, and HR, respectively, when the data were adjusted for body mass index. The estimates are somewhat higher for BP but similar for HR to those reported in previous family studies, suggesting that the distribution of the underlying etiologic factors in these sedentary families may be similar to those in the general population. There was substantial spouse resemblance in this study, which may be explained by a higher concordance for correlated lifestyle factors including diet, similar activity levels, or by assortative mating for relative weight or dietary preferences.

Familial clustering of insulin and abdominal visceral fat: the HERITAGE Family Study

Abdominal visceral fat (AVF) is an obesity-related phenotype thought to be associated with insulin resistance, diabetes mellitus, and atherosclerosis. Significant genetic influences on both AVF and insulin levels have been reported. However, information is lacking as to whether common genetic influences on AVF and insulin levels exist. AVF was assessed by computed tomography scan, and fasting insulin was measured by RIA in 512 members of 98 sedentary Caucasian families participating in the HERITAGE Family Study. Baseline data, collected before exercise training, were used in the present investigation. A bivariate familial correlation model was applied to evaluate whether there are familial influences that are common to insulin and AVF before and after adjustment for total fat mass (FM), and to assess the overall heritability of insulin and AVF. The maximal heritability for AVF, before and after adjustment for total FM, was 42% and 50%, respectively; and for insulin, it was 21%. Interestingly, 29% of the familial influences on insulin were also common to AVF, whereas 14% of the familial influences on AVF were shared by insulin. Furthermore, after AVF was adjusted for total FM, these common familial influences were increased to 48% and 20%. Genes and/or familial nongenetic factors with pleiotropic effects seem to influence both AVF and plasma insulin levels to a certain degree. Genes involved in the regulation of lipid storage and mobilization in the abdominal fat depot are potential candidates for these genetic pleiotropic effects.

Evidence for at least two major loci influencing human fatness

The genetics of human fatness has been the subject of many recent studies, motivated by the increased morbidity and mortality associated with obesity, as well as the increasing prevalence of overweight and obesity. The body-mass index (BMI) and fat mass (FM), measured by underwater weighing, were assessed for 1,630 individuals from approximately 300 families from phase 1 of the Quebec Family Study. The two phenotypes are highly correlated ( approximately .8) in adults, and previous segregation analysis revealed evidence for a recessive major gene for each trait. In our study, we utilized bivariate segregation analysis to determine the source(s) of phenotypic correlation-namely, a pleiotropic major gene, shared familial factors/polygenes, or shared nontransmitted environmental factors. Analysis was performed by use of the Pedigree Analysis Package, with extensions to the bivariate case. Tests of hypotheses provided evidence for two pleiotropic recessive loci, together accounting for 64% and 47% of the variance in BMI and FM, respectively. Under the model, all sources of phenotypic correlation were significant: 73% of the covariance was attributed to the pleiotropic major loci, 8% to residual familial effects, and 19% to nontransmitted environmental factors. The high degree of genetic identity between the two traits is not surprising, since the BMI often is used as a surrogate for FM; however, simultaneous analysis of both phenotypes enabled the detection of a second major locus, which apparently does not affect extreme overweight (as does the primary major locus) but which affects variation in the "normal" range.

Familial resemblance for VO2max in the sedentary state: the HERITAGE family study

This study investigates the familial resemblance of maximal oxygen uptake (VO2max) based on data from 86 nuclear families of Caucasian descent participating in the HERITAGE Family Study. In the current study, VO2max was measured twice on a cycle ergometer in 429 sedentary individuals (170 parents and 259 of their offspring), aged between 16 and 65 yr. The VO2max was adjusted by regression procedures for the effects of 1) age and sex; 2) age, sex, and body mass; and 3) age, sex, body mass, fat mass, and fat-free mass, as determined by underwater weighing. Evidence for significant familial resemblance was observed for each of the three VO2max phenotypes. Spouse, sibling, and parent-offspring correlations were significant, suggesting that both genetic and environmental factors contribute to the familial resemblance for VO2max. Maximal heritability estimates were at least 50%, a value inflated to an undetermined degree by nongenetic factors. The hypothesis of maternal inheritance, with the father's contribution being environmental, was also found to fit the data with estimates of maternal heritability, potentially associated in part with mitochondrial inheritance, reaching about 30%. These results suggest that genetic and nongenetic factors as well as maternal influences contribute to the familial aggregation of VO2max in sedentary individuals.

Familial resemblance for body composition measures: the HERITAGE Family Study

A sex-specific familial correlation model was used to assess the heritable contributions to several measures of body composition in 86 sedentary white families participating in the HERITAGE Family Study. For this study, sedentary families were recruited, tested for a battery of measures, endurance exercise trained for 20 weeks, and remeasured. This sample is unique in that activity level was controlled for in these families at baseline measurement. In this report, three body composition variables measured at baseline were analyzed, two indexing adiposity (total subcutaneous fat based on eight skinfold measurements [SF8] and percent body fat measured by underwater weighing techniques [%BF]) and one assessing fat free mass ([FFM] derived from underwater weighing). The maximal heritabilities for SF8 (34%) and %BF (62%) were consistent with those reported in previous studies. There were no sex nor generation differences in the familial correlations, and the spouse correlation was significant, consistent with the hypothesis that the familial aggregation reflects genetic and familial environmental factors. However, the results for FFM were very different. The most parsimonious pattern of familial resemblance was consistent with mitochondrial inheritance (i.e., mother-offspring and sibling correlations were equal and were larger than those for spouse and father-offspring pairs). Under the mitochondrial hypothesis, 39% of the variance was accounted for by familial/genetic effects. However, under a nonmitochondrial hypothesis, which could not be ruled out, 65% of the FFM phenotypic variance was accounted for by familial/genetic factors. This high heritability level, as compared with results from previous studies, is consistent with the hypothesis that activity may constitute an important environmental determinant of FFM. These alternative hypotheses for FFM warrant further investigation using complex multilocus-multitrait segregation models, which allow for major genetic, polygenic, and environmental sources of variance, as well as interactions among them.

Familial resemblance for abdominal visceral fat: the HERITAGE family study

OBJECTIVES

Abdominal visceral fat (AVF) is considered a risk factor for diabetes, atherogenic lipid profiles and hypertension. However, little is known about the genetic contribution to AVF as compared to total body fat.

DESIGN

AVF was assessed by computerized tomography, and total body fat (fat mass) was assessed by underwater weighing in 86 families participating in the Heritage Family Study. All family members were sedentary at baseline examination. The familial factors underlying the variability in age-adjusted AVF, age-fat mass-adjusted AVF and age-adjusted fat mass, were assessed using a familial correlation model.

RESULTS

The maximal heritability (including genetic and familial environmental effects) for AVF was comparable before (47%) and after (48%) adjusting for fat mass, and was 55% for fat mass itself in these sedentary families. Spouse correlations were significant for fat mass and for AVF prior to, but not after, adjustment for fat mass.

CONCLUSIONS

These results confirm the only previous study which investigated the familial aggregation of AVF (both in pattern and magnitude), suggesting that the factors underlying AVF in these sedentary families may be similar to those in the population at large. Although both genetic and familial environmental factors probably influence each of fat mass and AVF, there appears to be a predominantly genetic etiology for the visceral component which is independent of total body fat. These findings imply that some individuals are more at risk then others because of an inherited tendency to store abdominal fat viscerally rather than subcutaneously.

Cross-trait familial resemblance for body fat and blood lipids: familial correlations in the Quebec Family Study

In an attempt to better understand the genetic basis of the metabolic syndrome, we have undertaken a series of studies on the familial aggregation in the clustering of the coronary heart disease risk factors which characterize this syndrome. In the present study, the hypothesis of shared genetic (pleiotropy) and/or environmental factors between body fat and blood lipids is investigated by examining cross-trait (eg, father's body fat with his son's blood lipid) familial resemblance between 4 indicators of body fat (body mass index [BMI], sum of 6 skin folds [SF6]) and fat distribution (the ratio of the trunk to extremity skin folds adjusted [TER-sf] and unadjusted [TER] for SF6), and 5 blood lipid variables (total cholesterol [CH], triglycerides [TG], cholesterol associated with high-density lipoproteins [HDL], the CH/ HDL ratio and the difference between CH and HDL [CH-HDL]) measured in 1239 individuals from 309 families participating in the Quebec Family Study. A bivariate correlation model was used to obtain maximum likelihood estimates of cross-trait spouse, parent-offspring, and sibling correlations after adjustment of body fat and lipid data for the effects of age, separately in the four sex-by-generation groups. Likelihood ratio tests revealed the presence of significant (P < .05) cross-trait resemblance between body fat (BMI and SF6) and all lipid traits except CH and also between fat distribution (TER and TER-sf) and CH/HDL and CH-HDL. Only sibling cross-trait correlations were significant for all body fat-lipid pairs of measures, with bivariate familiality estimates (i.e., shared genetic and/or environmental factors) ranging from 8% to 40%. Although the hypothesis of genetic pleiotropy cannot be ruled out from the pattern of cross-trait correlations found in the present study, we conclude that environmental factors shared within sibships are probably more important than common genes in determining the covariation between body fat and blood lipids.

Familial resemblance of plasma lipids, lipoproteins and postheparin lipoprotein and hepatic lipases in the HERITAGE Family Study

The familial aggregation of lipids and lipoproteins and plasma postheparin triglyceride lipases was investigated in 86 Caucasian families participating in the HERITAGE Family study, a study investigating the role of genetic factors in the adaptation to exercise training and its relationships with cardiovascular disease risk factors. Accordingly, sedentary subjects were recruited, tested for a battery of measurements, exercise trained for 20 weeks, and were re-measured. The present report includes plasma levels of total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol and triglycerides, and postheparin plasma lipoprotein lipase (LPL) and hepatic lipase (HL) activities measured in 437 sedentary individuals (171 parents and 266 adult offspring) before training. Significant familial resemblance was observed for all the age-adjusted phenotypes. The pattern of familial correlations reveals no spouse correlations but significant parent-offspring and sibling correlations for total cholesterol, HDL-cholesterol and LDL-cholesterol with heritability (h2) estimates of 62%, 83%, and 50%, respectively. For plasma triglyceride concentrations (h2 = 55%) and HL activity (h2 = 40%), significant spouse correlations were found in addition to parent-offspring and sibling correlations, suggesting that common familial environment in addition to genetic factors contribute to the familial resemblance. For plasma LPL activity, there was no spouse correlation, but sex differences were found in the familial correlations with higher heritabilities in female pairs (h2 = 76%) compared to male pairs (h2 = 30%) and opposite-sex pairs (h2 = 44%). These results confirm the findings of previous family studies showing that genetic factors are major determinants of the familial resemblance in plasma lipids and lipoproteins and suggest the presence of sex differences in the heritability of postheparin LPL activity.

Segregation analysis of abdominal visceral fat: the HERITAGE Family Study

A major gene hypothesis for abdominal visceral fat (AVF) level, both before and after adjustment for total body fat mass, was investigated in 86 white families who participated in the HERITAGE Family Study. In this study, sedentary families were tested for a battery of measures (baseline), endurance exercise trained for 20 weeks, and then remeasured again. The baseline measures reported here are unique in that the variance due to a potentially important environmental factor (activity level) was limited. AVF area was assessed at L4 to L5 by the use of computerized tomography scan, and total body fat mass was assessed with underwater weighing. For fat mass, a putative locus accounted for 64% of the variance, but there was no evidence of a multifactorial component (i.e., no polygenic and/or common familial environmental effects). For AVF area, both a major gene effect accounting for 54% of the variance and a multifactorial component accounting for 17% of the variance were significant. However, after AVF area was adjusted for the effects of total level of body fat, the support for a major gene was reduced. In particular, there was a major effect for fat mass-adjusted AVF area, but it was not transmitted from parents to offspring (i.e., the three transmission probabilities were equal). The importance of this study is twofold. First, these results confirm a previous study that suggested that there is a putative major locus for AVF and for total body fat mass. Second, the findings from the HERITAGE Family Study suggest that the factors underlying AVF area in sedentary families may be similar to those in the population at large, which includes both sedentary and active families. Whether the gene(s) responsible for the high levels of AVF area is the same as that which influences total body fat content remains to be further investigated.

The impact of policy standardization on the Medigap market

This study examines the impact of policy standardization on the market for Medicare supplemental, or "Medigap," policies. Prior to 1992, insurance carriers could sell any benefits they chose, so long as minimum benefit requirements were met. In July 1992, federal legislation was implemented that required all new Medigap policies to conform exactly to one of 10 standardized sets of benefits. Using pre- and post-standardized policy information from six states, this study analyzes the impact of this legislation. Overall, standardization has affected the market positively, and as a result, consumers are better able to make informed choices about the benefits they are purchasing.