Phenotypic assortative mating in segregation analysis

A model of phenotypic assortative mating was developed for application in segregation analysis. The model assumed a constant spouse correlation across the range of a quantitative trait or the liability to a discrete trait. Four traits were analyzed to evaluate: 1) the feasibility of applying likelihood analysis to pedigree data in order to distinguish between assortative mating and shared environmental effects as the source of spouse correlation; and 2) the impact on segregation analysis of the failure to account for either assortative mating or shared environmental effects, as appropriate. Height ratio (the ratio of sitting to standing height) and eye color comprised the traits for which the observed spouse correlation reflected assortative mating; serum cholesterol and peptic ulcers (with genotypes defined by the ABO blood group) comprised the traits for which the observed spouse correlation reflected shared environmental effects. For all four traits the test statistics agreed with the known cause of spouse correlation; however, significance was not attained for height ratio or serum cholesterol. The ability to distinguish between the causes of spouse correlation in pedigree data presumably depends on trait and sample characteristics which remain to be delineated. Despite significant spouse correlation, its omission from the segregation analysis model did not undermine the inference of major locus inheritance for any of the four traits. However, the lack of an impact for these traits does not preclude an impact for other traits of ignoring the appropriate spouse correlation in segregation analysis.

HLA-linked rheumatoid arthritis

Twenty-eight pedigrees were ascertained through pairs of first-degree relatives diagnosed with rheumatoid arthritis (RA). RA was confirmed in 77 pedigree members including probands; the absence of disease was verified in an additional 261 pedigree members. Pedigree members were serologically typed for HLA. We used likelihood analysis to statistically characterize the HLA-linked RA susceptibility locus. The genetic model assumed tight linkage to HLA. The analysis supported the existence of an HLA-linked RA susceptibility locus, estimated the susceptibility allele frequency as 2.16%, and estimated the lifetime penetrance as 41% in male homozygotes and as 48% in female homozygotes. Inheritance was recessive in males and was nearly recessive in females. In addition, the analysis attributed 78% of the variance within genotypes to genetic or environmental effects shared by siblings. The genetic model inferred in this analysis is consistent with previous association, linkage, and familial aggregation studies of RA. The inferred HLA-linked RA susceptibility locus accounts for approximately one-half of familial RA, although it accounts for only approximately one-fifth of the RA in the population. Although other genes may account for the remaining familial RA, a large portion of RA cases may occur sporadically.

Evidence for multiple genes determining sodium transport

Sodium transport comprises a set of interacting systems. Consequently, a defective sodium transport gene affects multiple sodium transport systems, and a sodium transport variable measured on a sample of individuals reflects genetic variation from a number of different genes, complicating the task of identifying the effect of a single gene. To test for genes which affect sodium transport, we first applied principal components analysis to 14 variables related to sodium transport, thereby defining uncorrelated sources of variation in the variables. The sample consisted of 1,218 members of 68 pedigrees ascertained through probands with early-onset stroke, hypertension, or coronary heart disease. Segregation analysis of the 14 principal components scores provided evidence for 8 genetic variants which alter sodium transport. One of the 8 variants is recessive, has homozygous genotype frequency estimated as 8.8% of the population, and increases sodium-lithium countertransport, the passive sodium leak, body mass index, and triglyceride; the genetic variant may coincide with an insulin resistance gene. A second of the 8 variants is also recessive, has homozygous genotype frequency estimated as 7.4% of the population, and increases intraerythrocytic sodium and the passive sodium leak while decreasing sodium pump number; the genetic variant may reduce pump number. Two of the 8 variants substantially increase sodium-lithium countertransport; frequency estimates for heterozygotes for the dominant variant and homozygotes for the recessive variant equal 1.8% and 3.1%, respectively. Another of the 8 variants is recessive, has homozygous genotype frequency estimated as 1.9%, and increases body mass index. Each of the 3 remaining variants is rare and expressed in less than 1% of the sample.

Tabulations and expectations regarding the genetics of human hypertension

Results from family studies suggest several possible single gene traits may be related to essential hypertension in humans. Results of segregation analysis are reviewed for six possibly related traits (high sodium-lithium countertransport, low urinary kallikrein excretion, high fasting plasma insulin level, a fat pattern index, dense LDL subfractions, and body mass index). Eight genetic loci (on chromosomes 1, 6, 8, 17 and 19) are possibly related to essential hypertension in humans and are also reviewed. Two of them (GRA and AGT) are well-established. Glucocorticoid remediable aldosteronism (GRA) is attributable to a well-defined mutation on chromosome 8q21 and leads to the production of high levels of abnormal adrenal steroid hormones with subsequent aldosteronism, early severe hypertension, and strokes. This form of hypertension is unresponsive to ordinary medications but very responsive to glucocorticoid hormone administration. The angiotensinogen (AGT) locus on chromosome 1q4 has been related to hypertension in sibship linkage studies, association studies, and studies of angiotensinogen levels by genotype in three different populations (Utah, France, Japan). This locus seems to be associated with more severe essential hypertension and also with preeclampsia. Genetic heterogeneity, imprecision in measuring specific phenotypes, and variability in sampling methods in populations studied may all contribute to weaknesses and inconsistencies between reported studies. However, growing evidence for several single gene traits promoting susceptibility to hypertension offers opportunities for identifying genetically profiled subsets of patients in whom specific environmental interventions or specific types of medications will achieve more focused prevention and treatment of hypertension and its complications.

Genetic basis of familial dyslipidemia and hypertension: 15-year results from Utah

The genetic and environmental determinants of hypertension, lipid abnormalities, and coronary artery disease (CAD) have been studied for 15 years in Utah in population-based multigenerational pedigrees (2500 subjects among 98 pedigrees), twin pairs (74 monozygous and 78 dizygous), hypertensive siblings (131 sibships), siblings with CAD before age 55 (45 sibships), and anecdotally ascertained pedigrees with type II diabetes (271 subjects among 16 pedigrees), lipoprotein lipase deficiency (106 subjects in a single pedigree), and familial hypercholesterolemia (502 heterozygotes among 50 pedigrees). Estimates of heritability ranged from 20 to 75% for blood pressures and blood lipids. A strong positive family history predicts a future occurrence of hypertension (relative risk [RR] = 3.8) and CAD (RR = 12.7). Segregating single-gene effects were found for several 'intermediate phenotypes' associated with hypertension (erythrocyte sodium-lithium countertransport, intraerythrocytic sodium, a relative fat pattern, total urinary kallikrein excretion, and fasting insulin levels). Strong single-gene effects in segregation analysis were also found for low-density lipoprotein (LDL) cholesterol, lipoprotein (a) (Lp[a]), low high-density lipoprotein (HDL) cholesterol, and high apolipoprotein (apo) B. Deoxyribonucleic acid (DNA) markers of lipid abnormalities or hypertension have included LDL-receptor defects, lipoprotein lipase deficiency, high Lp(a), familial defective apo B, decreased quantitative levels of apo B, apo E phenotype, angiotensinogen, and 'glucocorticoid remediable aldosteronism (GRA) hypertension.' Also tested in Utah studies, but not found to be DNA markers for hypertension, were the genetic loci for the structural genes for renin and angiotensin-converting enzyme, and the sodium antiport system. In addition, important gene-gene interactions (LDL receptor with apo E2) and gene-environment interactions (kallikrein with potassium intake) were found.(ABSTRACT TRUNCATED AT 250 WORDS)

A gene-environment interaction between inferred kallikrein genotype and potassium

Urinary kallikrein excretion has been shown statistically to be partially determined by a major gene in large Utah pedigrees with the use of segregation analysis. A previous twin analysis of environmental factors influencing urinary kallikrein level showed that urinary potassium twin differences were strongly related to differences in urinary kallikrein. The present study uses 769 individuals in 58 Utah pedigrees to analyze the association of urinary potassium with urinary kallikrein within statistically inferred kallikrein genotypes. Fitting genotype-specific curves relating urinary kallikrein level to 12-hour urinary potassium amount within a major gene, polygene, and common environment model, we showed a significant statistical urinary potassium interaction with the inferred major gene for kallikrein (P = .0002). The heterozygotes (with a frequency of 50%) had a significant association between urinary kallikrein and potassium (slope, 0.51 +/- 0.04 SD), whereas there was no association with potassium in the low homozygotes, suggesting a genetic defect involving the kallikrein response to potassium. The model predicted that an increase in urinary potassium excretion of 0.8 SD above the mean in these pedigrees would be associated with high kallikrein levels in the heterozygotes similar to the high homozygotes. A decrease of 1.3 SD in urinary potassium excretion in heterozygous individuals was associated with kallikrein levels similar to the homozygous individuals with low kallikrein. Because in the steady state urinary potassium represents dietary potassium intake, this study suggests that an increase in dietary potassium intake in 50% of these pedigree members, estimated to be heterozygous at the kallikrein locus, would be associated with an increase in an underlying genetically determined low kallikrein level.(ABSTRACT TRUNCATED AT 250 WORDS)

Variance components/major locus likelihood approximation for quantitative, polychotomous, and multivariate data

Pearson [Philos Trans R Soc Lond [A] 200:1-66, 1903], Mendell and Elston [Biometrics 30:41-57, 1974], and Rice et al. [Biometrics 35:451-459, 1979] approximated the likelihood of the multifactorial model on a dichotomous phenotype by a procedure of successive univariate computation and conditioning. Hasstedt [Pap: Pedigree Analysis Package, Rev. 3. 1989] and Demenais [Am J Hum Genet 49:773-785, 1991] extended the algorithm to include a major locus. Here I extend the algorithm to polychotomous, quantitative, and multivariate phenotypes, add a major locus to the model, and describe and evaluate the accuracy of an approximation of the resulting variance components/major locus model.

Familial dyslipidaemic hypertension and other multiple metabolic syndromes

Data from several different studies are reviewed suggesting that a subset of hypertension is associated with metabolic abnormalities involving lipids, insulin, and often obesity, all aggregating strongly in families. Persons with 'familial dyslipidaemic hypertension (FDH)' have an especially high risk of early coronary disease. The clinical and biochemical features of FDH are compared with Reaven's Syndrome X, familial combined hyperlipidaemia, dense LDL subfractions, diabetes, impaired glucose tolerance, central and general obesity, pre-diabetes, pre-hypertension, and heterozygous lipoprotein lipase deficiency. Some contribution from major gene effects is suggested in specific subsets reported in several different genetic studies reviewed in this report. It seems likely that multiple metabolic abnormalities are genetically heterogeneous. The data also suggest significant contributions from environmental factors such as diet and physical activity.

Prevention of familial cardiovascular disease by screening for family history and lipids in youths

We analyzed medical family history information from 51,053 families of high school students in Utah and Texas and cholesterol measurements from 853 youths and 1618 adults in Utah families with cardiovascular disease (CVD) to assess the utility of different approaches to risk-factor evaluation for youths. The major question addressed was in which youths should blood cholesterol be tested? Applying National Cholesterol Education Program recommendations suggested that 36% in Utah and 38% in Texas be tested. Heterozygous familial hypercholesterolemia (hFH) is the best documented and most serious cholesterol disorder readily diagnosed in youths. In Utah families ascertained for CVD in adults, blood cholesterol levels among youths were significantly bimodal with hFH present in 84% of youths in the upper cholesterol mode. Blood cholesterol levels in adults from the same families were less bimodal with hFH present in 38% of adults in the upper mode. More overlap existed between high and normal modes in adults than in youths. Data from this study suggest that family histories and cholesterol concentrations obtained from high school students may meet the needs of cholesterol screening, education, and follow-up in a controlled and cost-effective setting.

Major gene effect for insulin levels in familial NIDDM pedigrees

Insulin resistance and hyperinsulinemia are familial traits that may precede and predict the onset of non-insulin-dependent diabetes mellitus (NIDDM). In some populations, the distribution of fasting insulin levels and measures of in vivo insulin action suggest the effects of a single major gene. We previously noted hyperinsulinemia among unaffected members of 16 large white pedigrees ascertained through two or more NIDDM siblings. To examine the hypothesis that insulin levels are determined by a single major genetic locus, we used segregation analysis to examine fasting insulin levels in 206 family members and 65 spouses who had normal glucose tolerance tests by World Health Organization criteria. Segregation analysis supported a major locus determining fasting insulin levels and segregating as an autosomal recessive allele with a frequency of 0.25. Thus, homozygotes represented 6.25% of the population, and homozygosity for the hyperinsulinemia allele elevated the mean fasting insulin level from 70.3 to 211.1 pM (11.7-35.2 microU/ml). The analysis apportioned the variance in fasting insulin as 33.1% due to the major autosomal locus, 11.4% due to polygenic inheritance, and 55.5% due to unmeasured effects. Homozygotes for the recessive allele had higher 1-h insulin levels than all others (911.7 vs. 427.2 pM [152.0 vs. 71.2 microU/ml]). We also found evidence for a major locus determining 1-h-stimulated insulin levels, with codominant inheritance as the most likely pattern in inheritance. The causal relationship between these findings and NIDDM has not been determined, and segregation of direct measures of insulin action remains to be demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Iron overload in Africa. Interaction between a gene and dietary iron content

BACKGROUND AND METHODS

In contrast to hemochromatosis, which in white populations is inherited through a gene linked to the HLA locus, iron overload in sub-Saharan Africa is believed to result solely from increased dietary iron derived from traditional home-brewed beer. To examine the hypothesis that African iron overload also involves a genetic factor, we used likelihood analysis to test for an interaction between a gene (the hypothesized iron-loading locus) and an environmental factor (increased dietary iron) that determines transferrin saturation and unsaturated iron-binding capacity. We studied 236 members of 36 African families chosen because they contained index subjects with iron overload. Linkage to the HLA region was tested with use of lod scores.

RESULTS

In the index subjects, increased iron was present in both hepatocytes and cells of the mononuclear-phagocyte system. Among family members with increased dietary iron due to the consumption of traditional beer, transferrin saturation in serum was distributed bimodally, with 56 normal values (less than 60 percent saturation) and 44 elevated values; the mean serum ferritin concentration was five times higher in the subjects with elevated transferrin saturation (P less than 0.005). The pedigree analysis provided evidence of both a genetic effect (P less than 0.005) and an effect of increased dietary iron (P less than 0.005) on transferrin saturation and unsaturated iron-binding capacity. In the most likely model, increased dietary iron raised the mean transferrin saturation from 30 to 81 percent and lowered the mean unsaturated iron-binding capacity from 38 to 13 mumol per liter in subjects heterozygous for the iron-loading locus. The hypothesis of tight linkage to HLA was rejected.

CONCLUSIONS

Iron overload in Africa may be caused by an interaction between the amount of dietary iron and a gene distinct from any HLA-linked gene.

Complex segregation analysis of autism

A complex segregation analysis of autism in 185 Utah families was carried out using the mixed model. The 209 affected individuals in these families represent nearly complete ascertainment of the autistic cases born in Utah between 1965 and 1984. The sibling recurrence risk for autism was 4.5% (95% confidence limits 2.8%-6.2%). Likelihoods were maximized for major-gene models, a polygenic model, a sibling-effect model, and a mixed model consisting of major-gene and shared-sibling effects. The analysis provided no evidence for major-locus inheritance of autism. Subdivision of the sample according to the probands' IQ levels showed that sibling recurrence risk did not vary consistently with IQ level. A segregation analysis of families in which the proband had an IQ less than 50 also failed to provide evidence for a major locus. However, because of the etiologic heterogeneity of this disorder, genetic analysis of other meaningful subsets of families could prove informative.

Are there interactions and relations between genetic and environmental factors predisposing to high blood pressure?

An overview of published observations suggests that both genetic predisposition and environment work together to produce hypertension in most persons. High blood pressure before age 55 occurs 3.8 times more often among persons with a strong positive family history of high blood pressure. Much of the total variability in blood pressure in modern populations seems attributable to genetic factors. Estimates of the proportion of the variance attributable to all genetic factors (heritability [H2]) vary from 25% in pedigree studies to 65% in twin studies for sitting diastolic blood pressure. Several biochemical traits associated with high blood pressure are highly genetic (H2, 78-84%) and may help elucidate the pathophysiology of high blood pressure. While pertinent environmental factors such as salt intake, alcohol use, and amount of exercise also correlate significantly among relatives, only 7% of the total variance of diastolic blood pressure seems attributable to all shared environmental factors in family households. Thus most familial aggregation of high blood pressure appears to be due to genes rather than shared family environment. Practical benefit may result from identifying familial predisposition in multiple siblings with high blood pressure before age 55 and lipid abnormalities (labeled "familial dyslipidemic hypertension"). About 12% of high blood pressure patients have familial dyslipidemic hypertension and also have high risk of early coronary heart disease. Hyperinsulinemia and central obesity as well as high triglycerides and low high density lipoprotein cholesterol are prominent features of familial dyslipidemic hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic traits related to hypertension and electrolyte metabolism

The genetic and cultural heritability and intercorrelation of traits related to hypertension have been carried out in 98 Utah pedigrees (2,500 person) and 58 sibships with two or more hypertensive persons (131 hypertensive persons). Although none of these traits has been established as a marker for "sodium-sensitive hypertension," many of them are related at least indirectly to both electrolyte metabolism and risk of hypertension. Significant recessive monogenic effects and high total heritability (52-84%) were found for urinary kallikrein, high fat pattern index, intraerythrocytic sodium, Na-Li countertransport, and ouabain binding sites. Familial correlations more strongly attributable to shared environment than to genetic effects were found for Na,K-ATPase pump activity, intraerythrocytic magnesium, plasma digoxin-like factor, plasma renin activity, and plasma sodium concentration. All anthropometric variables tested showed highly significant genetic heritability with low and insignificant shared family environmental effects. Several of the genetically determined cellular cation tests also correlated with other genetic traits including plasma lipids, anthropometric measurements, and other cellular cation tests. Among hypertensive individuals with familial dyslipidemic hypertension, plasma insulin levels correlated with obesity and lipid abnormalities and with several cellular cation flux tests associated with hypertension.

A prospective study of sodium-lithium countertransport and hypertension in Utah

A 7-year prospective study of a cohort of 1,458 normotensive adults from Utah pedigrees, screened from 1980 to 1985, was done to determine whether baseline levels of sodium-lithium countertransport were associated with an increased risk of future hypertension. Subsequent new hypertension (n = 39) was ascertained in 1989 from detailed follow-up medical questionnaires (67% response). Previous segregation analyses on a subset of these pedigree members who responded (n = 342) using family relationships in addition to countertransport levels have shown statistically inferred major gene segregation of sodium-lithium countertransport levels. In the normotensive adults inferred by segregation analysis to carry the recessive major gene for high sodium-lithium countertransport, new-onset hypertension occurred in 18.8% (3 of 16) compared with 3.7% (12 of 326) in the low sodium-lithium countertransport genotype group (relative risk, 4.6 [1.6, 13.9]; p = 0.03). However, an elevated baseline sodium-lithium countertransport level without genotype information from segregation analysis did not increase the risk of future hypertension in the complete cohort of adult pedigree members (relative risk, 1.02 [0.85, 1.22]). Adjustment for other risk factors reduced the relative risk to 0.90 (0.72, 1.11). We conclude that the presence of a major gene for sodium-lithium countertransport or another closely linked gene, rather than the actual level of sodium-lithium countertransport, may increase the risk of hypertension onset. High sodium-lithium countertransport levels do not increase the risk of future hypertension for individuals in whom only polygenic and environmental effects determine sodium-lithium countertransport level.(ABSTRACT TRUNCATED AT 250 WORDS)

A variance components/major locus likelihood approximation on quantitative data

The variance components/major locus model encompasses a major locus, a polygenic component, and shared environmental effects. The model attributes familial correlations to polygenic and shared environmental effects when testing for major locus inheritance or accounts for the major locus when estimating variance components. Because exact computation of the likelihood of the variance components/major locus model on quantitative data requires excessive computer time, I developed an approximation. The approximation retained the general shape of the likelihood surface. Accuracy of the approximation did not vary consistently with allele frequency or the size of the major locus effect.

Multigenic human hypertension: evidence for subtypes and hope for haplotypes

Hypertension that occurs before the age of 60 years is strongly aggregated in families, mostly due to genetic factors with weaker contributions from a shared family environment. Hypertension is probably a heterogeneous collection of overlapping subsets of pathophysiological mechanisms, such as dyslipidemia, obesity, hyperinsulinemia and cation metabolism. Highly heritable traits such as sodium-lithium countertransport, urinary kallikrein excretion and a body fat pattern index show evidence of major gene segregation in families with hypertension. They are thought to be intermediate phenotypes in the chain of pathophysiological events leading from specific genes to the distant phenotype of hypertension. They provide evidence of measurable contributions from single gene traits to the susceptibility to hypertension. Genetic linkage studies have suggested that other specific loci (e.g. histocompatibility leukocyte antigen, blood group MN and the haptoglobin protein) contribute to the susceptibility to hypertension. DNA sequencing has shown a point mutation for lipoprotein lipase that conveys susceptibility to lipid abnormalities, and possibly also hypertension, as seen in families with dyslipidemic hypertension. Further application of these approaches, especially in families that include multiple siblings with hypertension, shows promise of a true understanding of how the combined effects of a few specific genes, the polygenic background and selected environmental factors can lead to essential hypertension. This understanding should foster better tailored and more effective approaches to the prevention, diagnosis and treatment of hypertension.

Population-based frequency of dyslipidemia syndromes in coronary-prone families in Utah

The frequency of familial dyslipidemia syndromes was determined from blood tests in 33 objectively ascertained families with early coronary heart disease (CHD) (two or more siblings with CHD by the age of 55 years). Three fourths of persons with early CHD in these families had 90th percentile lipid abnormalities (cholesterol level at or above the 90th percentile, triglyceride level at or above the 90th percentile, and/or high-density lipoprotein cholesterol (HDL-C) level at or less than the 10th percentile). The HDL-C and triglyceride abnormalities were twice as common as low-density lipoprotein-cholesterol abnormalities. The most common syndromes found were familial combined hyperlipidemia (36% to 48% of families with CHD), familial dyslipidemic hypertension (21% to 54% of families with CHD), and isolated low levels of HDL-C (15%), with overlapping familial dyslipidemic hypertension with familial combined hyperlipidemia and low-level HDL-C. Well-defined monogenic syndromes were uncommon: familial hypercholesterolemia being 3% and familial type III hyperlipidemia, 3%. Another 15% of families with CHD had no lipid abnormalities at the 90th percentile. Physicians should learn to recognize and treat these common familial syndromes before the onset of CHD by evaluating family history and all three standard blood lipid determinations. Failure to recognize and treat them leaves affected family members at high risk of premature CHD.

Genetics of hypertension: what we know and don't know

Human arterial hypertension is likely a multifactorial trait resulting from multiple measurable monogenes, blended polygenes, shared family environment, and individual environment. Familial aggregation of hypertension and familial correlation of blood pressure appears to be more due to genes than to shared family environment. Total genetic heritability of 80% with some recessive major gene effects have been found for several traits associated with hypertension including urinary kallikrein excretion, intraerythrocytic sodium, and sodium-lithium countertransport. Other interesting factors regarding hypertension genetics include: non-modulation of the renin angiotensin system, intralymphocytic sodium, ionized calcium, and several genetic markers such as haptoglobin, HLA, and MNS blood type. Probably the most clinically useful information regarding the genetics of hypertension is evolving in several studies reporting a strong association of hypertension with dyslipidemia, diabetes, and obesity.

Current knowledge regarding the genetics of human hypertension

Observations over 11 years from the University of Utah Cardiovascular Genetics Research Clinic and published data from other studies are reviewed to illustrate research approaches, developing results and prospects for future studies. Strong associations with hypertension have been found for several biochemical tests that show substantial genetic determination. Suggestions of recessive major gene effects and significant polygenic background determinations have been found for several variables, including urinary kallikrein excretion, intracellular sodium concentration, sodium-lithium countertransport and sodium-potassium cotransport. Each of these variables is related in some way to sodium or potassium metabolism, or both, and may help to improve the understanding of a possibly inherited susceptibility to hypertension that is related to dietary electrolyte intake. A second major group of factors involving familial predisposition to hypertension include lipid abnormalities (increased very-low- and low-density lipoprotein cholesterol and decreased high-density lipoprotein cholesterol); increased fasting insulin levels or insulin resistance, or both; obesity (especially central or upper body obesity); and multiple environmental factors influencing these metabolic systems, including dietary fat, carbohydrate and calorie intake; physical exercise; and certain antihypertensive medications that adversely affect lipid metabolism and glucose tolerance. Some studies even suggest a possible link between these two large groups of factors (electrolyte metabolism and lipid-insulin metabolism). Hypertriglyceridaemia and hyperinsulinaemia are both significantly correlated with increased levels of several cation-flux tests. It is recommended that studies of human hypertension apply these biochemical profiles to study sibships with two or more hypertensive siblings as a cost-effective initial approach.(ABSTRACT TRUNCATED AT 250 WORDS)

Recessive inheritance of a relative fat pattern

We defined a relative-fat-pattern index (RFPI) as the ratio of subscapular skinfold thickness to the sum of subscapular and suprailiac skinfold thicknesses and computed RFPI for 774 adults (age greater than or equal to 25 years) in 59 pedigrees ascertained through cases of cardiovascular disease. Likelihood analysis of RFPI supported recessive inheritance of an allele with a frequency of 46%, which elevated mean RFPI from .412 to .533 when homozygous. The analysis apportioned the variance in RFPI as 42.3% due to the major locus, 9.5% due to polygenic inheritance, and 48.2% due to random environmental effects. Homozygotes for the recessive allele tended to have small suprailiac skinfold thicknesses rather than large subscapular skinfold thicknesses. Homozygotes were more frequent in younger than in older cases of obesity, coronary heart disease, essential hypertension, and diabetes mellitus; the increase was significant for all but diabetes.

Recessive inheritance of a high number of sodium pump sites

The number of sodium pump sites on erythrocytes was measured on 1,847 individuals in 80 Utah kindreds ascertained through probands with cardiovascular disease. Likelihood analysis supported recessive inheritance of high pump number. The major locus explained 14.0% of the variance in pump number; polygenic inheritance explained another 63.4%. Homozygotes for the recessive allele occurred with a frequency of 1.74% and had a mean pump number estimated as 566.0 sites/red blood cell (RBC) versus a mean of 312.2 sites/RBC for the other genotypes. Young individuals with the high pump number genotype were leaner, and older adults with the high pump number genotype were heavier. Diabetes and early hypertension were more prevalent in women with the high pump number genotype. Although not significant, obesity in adults of both sexes and early coronary heart disease in men were more prevalent in individuals with the high pump number genotype.

Genetic heritability and common environmental components of resting and stressed blood pressures, lipids, and body mass index in Utah pedigrees and twins

The relative contributions of genes and shared environment to cardiovascular risk factors were studied in twins and pedigrees in 1983-1985. Sitting, standing, isometric hand grip, bicycling, and mentally stressed (serial subtraction) blood pressures were obtained from 146 male monozygous twins, 162 male dizygous twins, and 1,102 healthy adults in 67 Utah pedigrees. Fasting total plasma cholesterol, triglycerides, high density lipoprotein cholesterol (HDL), and body mass index were also measured. Heritability was estimated before and after adjusting for 12 environmental variables (measures of socioeconomic status; personality types; exercise levels; use of tobacco, alcohol, coffee, etc.) by using age-adjusted twin intraclass correlations. These heritabilities were compared with those obtained from a variance components analysis of the pedigree data separating genetic and common household effects. Sitting and standing blood pressure heritability estimates were much higher from twin than from pedigree data (39-63% in twins vs. 16-22% in pedigrees), as were those for cholesterol and triglycerides (65 and 75% from twins vs. 42 and 37% from pedigrees) and body mass index (51 vs. 21%). Estimates were similar for heritability of HDL cholesterol (51 vs. 45%). Most of the stressed blood pressure heritabilities were similar to sitting blood pressure estimates. No common household effect (except for adjusted HDL cholesterol (24%), p less than 0.01) was statistically significant for the lipids, blood pressures, or body mass index. Environmental variables correlated much better in monozygous twins and spouses than in dizygous twins, brothers, or sisters. Spouse correlations for lipids, blood pressures, and body mass index were low, with a maximum of 0.12 (p less than 0.05) for HDL cholesterol. We conclude that genes contribute much more than shared environment to the well-recognized familial correlation of blood pressures, lipids, and body mass index.

A gene for high urinary kallikrein may protect against hypertension in Utah kindreds

The inheritance of 12-hour overnight total urinary kallikrein excretion and its association with family history of essential hypertension were studied in 405 normotensive adults and 391 youths in 57 Utah pedigrees. Total urinary kallikrein excretion was highly familial with 51% of the total variance attributable to a dominant allele for high total urinary kallikrein excretion and 27% attributable to the combined effects of polygenes and shared family environment. An estimated 28% of the population has one or two copies of the dominant allele for high total urinary kallikrein excretion (2.3 SD units higher than the low homozygotes). About 83% of the population could be assigned to one of the two genotypic populations. Individuals with the high total urinary kallikrein excretion genotype were significantly less likely to have one or two hypertensive parents (relative odds = 0.56, p = 0.042). We conclude that a dominant allele expressed as high total urinary kallikrein excretion may be associated with decreased risk of essential hypertension. Further studies should be performed to confirm this finding and to test for interactions between this apparently protective gene and other genetic and environmental determinants of essential hypertension.

Estimation of genetic model parameters: variables correlated with a quantitative phenotype exhibiting major locus inheritance

A major locus that is detected through its effect on one phenotype (a primary trait) may also affect other quantitative phenotypes or qualitative disease endpoints (secondary traits). The pattern of effects of the major locus on a set of primary and secondary traits suggests candidate defects for the mutant allele. The effects are directly estimable when "measured genotypes" or a tightly linked marker allow unambiguous assignment of major locus genotypes. When genotypes assignments are ambiguous for a major locus detected through its effect on a quantitative primary trait, we propose estimators using genotypic probabilities. Making certain reasonable assumptions, we demonstrate asymptotic unbiasedness of these genotypic probability estimators of the genotypic means and variances for either the quantitative primary or secondary traits, of the covariances between quantitative primary and secondary traits, and of prevalences for the secondary qualitative traits. An important application of genotypic probability estimators is to define an effect of a major locus that cannot be detected upon analysis of the variable; for example, major locus effects may be defined for hypertension or blood pressure as secondary traits, but not detected as primary traits.