Hoarseness as the initial clinical presentation of anomalous left coronary artery from the pulmonary artery

Anomalous origin of the left coronary artery from the pulmonary artery is a rare congenital anomaly that, if left untreated, will most often result in severe myocardial ischemia and significant morbidity and mortality. We report an unusual presentation of this defect in a 2-month-old infant who had an initial complaint of a "hoarse cry." We theorize that impingement of the recurrent laryngeal nerve due to dilatation of the pulmonary artery was the most likely etiology of the patient's symptoms. This case serves as an important reminder that serious congenital heart disease may present with any number of complaints and unusual findings.

Autoregulation of cerebral blood flow in fetuses with congenital heart disease: the brain sparing effect

Fetuses with congenital heart disease (CHD) have circulatory abnormalities that may compromise cerebral oxygen delivery. We believe that some CHD fetuses with decreased cerebral oxygen supply have autoregulation of blood flow that enhances cerebral perfusion (brain sparing). We hypothesize that cerebral autoregulation occurs in CHD fetuses, and the degree of autoregulation is dependent on the specific CHD and correlates with intrauterine head circumferences. CHD fetuses were compared to normal fetuses. Data included cardiac diagnosis, cerebral and umbilical artery Doppler, head circumference, weight, and gestational age. The cerebral-to-placental resistance ratio (CPR) was assessed as a measure of cerebral autoregulation. CPR = cerebral/umbilical resistance index (RI) and RI = systolic-diastolic/systolic velocity (normal CPR > 1). CPR > 1 was found in 95% of normal vs 44% of CHD fetuses. The incidence of CPR < 1 was greatest in hypoplastic left or right heart fetuses. Compared to normal, cerebral RI was decreased in CHD fetuses. The CPR vs gestational age relationship, and the relationship among weight, head circumference, and CPR differed across normal and CHD fetuses. Fetuses > 2 kg with CHD and a CPR < 1 had smaller head circumferences than normal. Brain sparing occurs in CHD fetuses. Fetuses with single ventricular physiology are most affected. Inadequate cerebral flow in CHD fetuses, despite autoregulation, may alter brain growth.

Childhood passive smoking, race, and coronary artery disease risk: the MCV Twin Study. Medical College of Virginia

BACKGROUND

Children with long-term exposure to passive cigarette smoke may be at elevated risk for the development of premature coronary artery disease (CAD).

OBJECTIVE

To examine how CAD risk factors, exposure to passive smoking, sex, and race are related in pubertal children and to determine if there is an identifiable childhood risk profile (i.e., does passive smoking interact with other coronary risk factors to increase the risk of developing premature CAD).

DESIGN

Cohort analytic study.

SETTING

The Medical College of Virginia (MCV) Twin Study, Richmond, Va.

SUBJECTS

Randomly selected twins from 408 11-year-old twin pairs recruited from nearby schools.

METHODS

Data collection occurred at 18-month intervals on family and health histories, smoking and alcohol consumption, blood pressure, anthropometrics, and biochemical assays. Data from cohorts of 11-year-olds studied through age 15 years were analyzed by repeated-measures analyses of variance using a mixed modeling approach. Models for high-density lipoprotein cholesterol (HDL-C) included race, sex, passive smoking status, weight, systolic and diastolic blood pressures, and all interactions.

RESULTS

Passive smoke exposure was greater in white families than in black families. Levels of HDL-C and HDL2-C (HDL subfraction 2 cholesterol) were lower in white children than in black children (visit 1: HDL-C, mean +/- SD, 1.21+/-0.26 vs. 1.31+/-0.26 mmol/L [47.0+/-10.1 vs. 50.6+/-10.1 mg/dL], P< or =.01; HDL2, mean +/- SD, 0.31+/-0.18 vs. 0.41+/-0.19 mmol/L [12.3+/-7.0 vs. 15.9+/-7.4 mg/dL], P< or =.001). Children with a family history of cardiovascular disease had differences in HDL-C levels related to race that were worsened by exposure to cigarette smoke. In these children, HDL-C level was lower in those exposed to passive smoking (visit 1: 1.18+/-0.23 vs. 1.25+/-0.23 mmol/L [45.6+/-9 vs. 48.2+/-9 mg/dL] and visit 4: 0.98+/-0.10 vs. 1.19+/-0.18 mmol/L [37.8+/-4 vs. 46.0+/-7 mg/dL]; P<.001), with white children having lower HDL-C levels than black children (visit 1: 1.12+/-0.21 vs. 1.36+/-0.23 mmol/L [43.2+/-8 vs. 52.7+/-9 mg/ dL] and visit 4: 0.97+/-0.31 vs. 1.01+/-0.31 mmol/L [37.6+/-12 vs. 39.0+/-12 mg/dL]; P = .004). In white families, as weight increased, boys exposed to passive smoking showed the greatest decrease in HDL-C level (P<.01 for weight by sex and passive smoking interaction). Risk factors for CAD, such as blood pressure, interacted with HDL-C and these relationships varied by race and sex.

CONCLUSIONS

Pubertal children with long-term passive cigarette smoke exposure have lower HDL-C levels. Racial differences in HDL-C levels are related to passive smoke exposure. In children with a family history of cardiovascular disease, interactions exist between passive smoking, HDL-C level, and blood pressure that differ by sex and race. White males exposed to passive smoking who have a family history of cardiovascular disease and higher weights and diastolic blood pressures may be at special risk for premature CAD.

Balloon dilation of discrete subaortic stenosis associated with other cardiac defects in children

Balloon dilation (BD) is reported as an effective treatment for isolated discrete thin membranous subaortic stenosis (SAS). We asked if BD of SAS with associated cardiac defects: 1) is effective; 2) creates or worsens mitral insufficiency in the presence of valvar membrane attachment; and 3) creates or worsens aortic insufficiency. BD was performed on 13 patients (9 females, 4 males with a mean age of 5.8 years and an age range of 1-14 years old) for SAS with the following associated defects: VSD (6 patients), coarctation (4 patients), complete atrioventricular canal (1 patient), tetralogy of Fallot (1 patient), and abnormal mitral valve (4 patient). Prior intracardiac surgical procedures (3 for SAS resection) had been performed in 46% of the study group. Peak gradient was reduced from 53 +/- 40 mmHg to 31 +/- 25 mmHg (p < 0.01). The resulting gradient was related to the predilation gradient (r = 0.71; p =.006). Thin membranes (< 3 mm) were associated with lower initial gradient (p < 0.02), lower resulting gradient (p < 0.001) and a greater percent gradient reduction (76% versus 36%; p < 0.01). Aortic insufficiency, which was present predilation in 77%, did not change and was not created in any patient. Mitral valve membrane attachment was present in 69% and associated with a lower resulting gradient (p < 0.006). Mitral insufficiency was not created in 10 patients, was unchanged in 2 and was improved in 1 patient. Surgical procedures were ultimately required in 8 patients during follow-up. BD of SAS associated with other cardiac defects achieves the following: 1) reduces SAS gradient in selected patients without creating or worsening aortic insufficiency; 2) does not create or worsen mitral insufficiency when mitral valve membrane attachment is present; 3) improves preoperative hemodynamics; and 4) is unlikely to be effective in post-surgical recurrence.

Tracking of left ventricular mass in children: race and sex comparisons: the MCV Twin Study. Medical College of Virginia

BACKGROUND

Increased left ventricular (LV) mass is a predictor of cardiovascular disease in adults. The mechanism(s) for these observations are not fully understood.

METHODS AND RESULTS

We repeatedly studied a biracial sample of children from ages 11 through 17 years. At visits 1 through 5, height, weight, and pubertal stage were determined. Blood pressure and heart rate were measured. M-mode and two-dimensional echocardiograms were performed with a 3.5-MHz transducer with the subject in the supine position. LV mass was calculated. Repeated-measures analysis using a mixed modeling approach was performed for LV mass. At all ages, boys had greater LV mass than girls. For the population as a whole, we found significant tracking correlations for LV mass between each interval of measurement and throughout the entire period of examination. The tracking correlation for the entire sample from visit 1 through visit 5 was r=.41. The LV mass in white children tracked from the youngest to the oldest. Black children tracked similarly from ages 1 to 15 years, but tracking was not significant across the widest interval, visit 1 through visit 5. Racial differences were found in the interactions of systolic blood pressure and heart rate, which magnified the differences in LV mass. During adolescence, LV mass tracks significantly in both black and white children.

CONCLUSIONS

Interactive effects such as weight, blood pressure, and heart rate magnify sex and race differences in LV mass.

Genetic regulation of hemodynamic variables during dynamic exercise. The MCV twin study

BACKGROUND

Both resting and exercise levels of blood pressure in individuals have been used as predictors of adult hypertension. One possible mechanism underlying the relation between childhood resting and exercise blood pressure and future blood pressure is a set of genes expressed in childhood that persists to regulate adult blood pressure.

METHODS AND RESULTS

To investigate the genetic relation of blood pressure and heart rate during both rest and exercise, we asked: (1) Are the genes that regulate resting hemodynamic variables the same genes that regulate these variables during exercise? (2) How much of the variance in exercise hemodynamic variables is genetic and how much is environmental? (3) Do the genetic and environmental influences on hemodynamic responses change with increasing levels of exercise? To determine how genetic and environmental effects expressed at rest influenced responses during dynamic exercise, a genetic analysis was conducted by fitting a series of models to the covariance matrices with the use of the LISREL VII program.

CONCLUSIONS

We found that all the genetic effects expressed at the later stages of exercise can be explained by genetic effects expressed at rest and at the first stage of exercise. The environmental effects appear to be workload specific and include errors of measurement.

Advances in preventive cardiology

Since the publication of the Report of the Expert Panel on Blood Cholesterol in Children in 1991, both multi-institutional and office-practice-based studies have attested to its diet recommendations' safety and efficacy in modestly lowering blood cholesterol. Normal growth was preserved. Investigators have found no aberrations of either macro- or micronutrients. Although the dietary changes recommended appear effective, the screening recommendations have been vigorously questioned, with adherents on both sides with opinions from never screen to universal screening. Conventional medical wisdom states that smoking is bad for smokers' health. The ill health effects have been extended to passive smoking. Previous studies have shown effects of maternal smoking on the birth-weight of the newborn. Now studies are emerging that show long-time effects of in utero smoke on coronary risk factors.

Modulation of atrial repolarization by site of pacing in the isolated rabbit heart

BACKGROUND

Single-site or multisite atrial pacing may reduce the incidence of atrial fibrillation in humans. The therapeutic mechanisms may include synchronization of atrial repolarization (repolarization "memory") and/or decreased dispersion of atrial repolarization. These responses have not been well documented in intact atria.

METHODS AND RESULTS

Monophasic action potential recordings were made from six atrial epicardial sites in 39 isolated perfused rabbit heart preparations during 3 hours of continuous right atrial, left atrial, or biatrial pacing. Action potential recordings obtained at times 0, 45, 90, 135, and 180 minutes were computer analyzed for activation time (AT) and 90% action potential duration (APD) at each site. No consistent relationship could be demonstrated between APD and AT at any time during atrial pacing (all P > .05). On average, left atrial APDs were longer than right atrial APDs by up to 6.3 ms at all times, regardless of the site of pacing (P < or = .05). At all times, dispersion of atrial repolarization was minimized by left atrial pacing compared with right atrial pacing (21.6 +/- 9.1 versus 32.4 +/- 15.1 ms, respectively, at time 0; P < .05). Biatrial pacing provided no further reduction in dispersion of repolarization compared with left atrial pacing (all P > .05).

CONCLUSIONS

No relationship can be demonstrated between atrial AT and APD in the isolated rabbit heart preparation. This differs from ventricular repolarization "memory," which is demonstrable under the same conditions. Left atrial APD is, on average, longer than right atrial APD, suggesting spatial heterogeneity in repolarization. Dispersion of atrial repolarization is minimized by left atrial pacing in this preparation with no further advantage to biatrial pacing.

Genetic influences on ambulatory blood pressure patterns. The Medical College of Virginia Twin Study

The genetic influence of ambulatory blood pressure and heart rate was examined in 38 pairs of monozygotic twins, 17 pairs of same-sex dizygotic twins, and 11 pairs of opposite-sex dizygotic twins, all aged 15 or 17 years. The data were analyzed taking into consideration that the response was multivariate (24-h values) instead of the usual univariate response. The results demonstrated the heritability of ambulatory blood pressure and heart rate. This was true regardless of whether the estimate of heritability involved monozygotic twin pairs compared to same-sex dizygotic twin pairs only, or all dizygotic twin pairs. The time-related intraclass correlation coefficient within each twin classification indicated that the patterns of response within twin pairs correlated more for monozygotic twin pairs than within twin pairs for either set of dizygotic twin pairs. In addition, although the opposite-sex dizygotic twin pairs may have different mean levels of response, they exhibit a similarity of patterns of response akin to that seen within same-sex dizygotic twin pairs.

New perspectives in childhood blood pressure

Ambulatory blood pressure monitoring is a new technique available to the pediatric cardiologist, and several studies have investigated its usefulness. Investigators are now providing data for both normal values and reproducibility. Other authors have examined the effects of hypertension in mothers upon their offspring, which include small birthweight and possible developmental delay. New data, particularly from the Bergen Blood Pressure Study, indicate that maternal hypertension may be a precursor for future blood pressure elevation in offspring. It is known that obese people are more likely to be hypertensive. A study performed in China in a lean population, including individuals who were relatively obese, showed the positive relation of body weight to blood pressure. Furthermore, data now emerging indicate that both retinal vessels and renal arteries in children suffer changes with persistently elevated blood pressure. This clearly is something to follow. Other articles examined in this review investigate the relation of atherosclerosis to hypertensive disease.

Altered blood pressure reactivity in adolescent diabetics

OBJECTIVE

We examined hemodynamic responses to a variety of physiologic stimuli in 14 normotensive adolescents with type I diabetes and 45 healthy controls to determine whether structural vascular changes contribute to a reduced vasodilator capacity in adolescent diabetics. We asked, in adolescents with type I diabetes: (1) Are structural vascular changes present? (2) Are changes in the systemic vascular bed reflected in abnormal blood pressure regulation? and (3) Is abnormal vascular reactivity associated with either diabetes duration or control?

METHODOLOGY

Diabetic subjects were outpatients treated at the Medical College of Virginia, ages 13 to 18 years. Diabetes duration averaged 7.5 years. Each subject underwent an echocardiogram, dynamic and isometric exercise testing, and forearm plethysmography.

RESULTS

Compared to controls, diabetic subjects had (1) higher systolic and diastolic blood pressure during dynamic and handgrip exercise, (2) decreased forearm vasodilator capacity in response to ischemia, and (3) an increased aortic peak velocity. Group diastolic filling abnormalities were found, but these did not persist after adjustment for heart rate. The following variables were related to both diabetes duration and control (average glycosylated hemoglobin): (1) diastolic blood pressure during dynamic exercise, (2) resting forearm vascular resistance, and (3) forearm vascular reactivity. In addition, diabetes duration correlated with isometric exercise diastolic blood pressure, and diabetes control correlated with resting diastolic blood pressure.

CONCLUSION

In young diabetics we found that (1) abnormalities of the resistance vessels of the forearm may be present, (2) the degree of vascular change is related to diabetes duration and control, and (3) aortic distensibility may be impaired.

Hypertension and atherosclerosis in children

This article reviews important advances in the understanding and treatment of hypercholesterolemia and persistently high blood pressure in children. Two plant sterols, sitosterol and sitostanol, have been tested in prepubertal and adolescent children with hypercholesterolemia and appear promising. The advantages and disadvantages of family history in screening algorithms for atherosclerotic disease are discussed. Additionally, the apolipoproteins are being used more frequently to screen for cardiovascular risk. A rare genetic disease, familial defective apolipoprotein B-100, causes hypercholesterolemia. The distinction between this disease and familial hypercholesterolemia has therapeutic implications. Two studies show that in utero exposures influence the future development of hypertension. Intrauterine cocaine exposure was associated with persistently elevated blood pressure during later childhood. The mechanism may involve the sympathetic nervous system. Retarded fetal growth appears to be a risk factor for the presence of hypertension during adult years in men.

Cardiovascular reactivity in isometric exercise and mental arithmetic in children

In children, we studied noninvasively the cardiovascular stress responses, including changes over time of systolic blood pressure (SBP), heart rate (HR), and stroke volume (SV) in isometric handgrip (IHG) and mental arithmetic. Specifically, we asked whether 1) these cardiovascular stress responses were different for the two stress conditions in children, 2) these responses differed in boys and girls, and 3) the anthropometric variables related to these stress responses. SV differed significantly between IHG and mental arithmetic over the entire stress period. This may reflect higher systemic vascular resistance during IHG. HR in boys was lower than in girls over the entire period of stress in both stress tests. This observation cannot be attributed to differences in conditioning, because this should not influence responses to isometric or mental stress. A larger left ventricular mass was related to higher SVs. A marked relationship was found between HR and SBP and between HR and SV. No relationship was found between SBP and SV.

Investigation of the influences of puberty, genetics, and environment on the composition of subgingival periodontal floras

The classical twin model was utilized in this study in an attempt to determine the importance of host genetics to the composition of the subgingival flora. Simultaneously, the effect of puberty on the flora composition was assessed. The compositions of the floras were significantly different at ages 11 and 14 in the same people, indicating that transition to an adult flora composition may be initiated during puberty. However, the numbers of subjects who had prepubertal and postpubertal testosterone levels in this study were too small to demonstrate significant differences based solely on testosterone level (P = 0.053 and 0.11 for tests of unrelated members, i.e., all twins "a," the first twin of each pair, and all twins "b," the second twin of each pair). Sixteen unrelated 11-year-old subjects had prepubertal levels of less than 30 ng of testosterone per dl of serum, and only six of these unrelated subjects had levels above 300 ng/dl by age 14. Of their twin siblings, who formed the second group of unrelated individuals, 15 had prepubertal levels and only 5 reached postpubertal levels. Unpaired t tests indicated that Veillonella atypica, Prevotella denticola, and Prevotella melaninogenica were among the species that contributed most to changes in flora composition during puberty. The compositions of subgingival floras of 11-year-old monozygous and dizygous male twins were significantly more similar than those of unrelated subjects in the study (P = 0.004 and 0.009, respectively). At 12.5 years of age, the floras of monozygous twins remained more similar than those of unrelated subjects (P = 0.001), but the dizygous-twin floras were not significantly more similar than those of unrelated people. This difference corresponded with moderate and varied testosterone levels within dizygous-twin pairs at age 12.5. By age 14 both monozygous and dizygous twins again had floras with compositions more similar than those of unrelated people (P = 0.008 and 0.002, respectively). Estimates of the genetic contributions to the increased similarity of the floras of twins as compared with floras of unrelated people indicated that the concentrations of several species in the flora may be influenced by host genetic factors. The prevalence of certain other species appeared to be controlled primarily by environment.

Univariate genetic analysis of oxygen transport regulation in children: the Medical College of Virginia Twin Study

We investigated the relative contributions of genetic, individual environmental, and shared environmental effects on 2,3-diphosphoglycerate (DPG) regulation in preadolescent children. In a population of 165 early pubescent boy and girl twin pairs (11.4 y old), of whom 63 were passive smokers, we asked: 1) Are there differences in the control of DPG levels between early pubertal boys and girls? 2) If present, are these differences influenced by exposure to passive cigarette smoke? Non-passive-smoking boys and girls had similar DPG levels. With exposure to passive smoke, DPG levels increased in boys (p = 0.02) but not in girls. Analysis of variance on DPG demonstrated a parental smoking effect (p = 0.008) and suggested an interactive effect between parental smoking and sex of the child (p = 0.08). Univariate genetic analyses suggested that genes operated at different magnitudes in boys (9%) and girls (39%) in explaining a significant portion of the variance in DPG. The magnitude of shared environmental influences was greater in boys (62%) than in girls (34%), whereas individual environmental effects were similar in boys (29%) and girls (26%). Early pubertal boys differ from girls in their regulation of DPG. Environmental stressors such as passive cigarette smoke may elicit different responses in males and females, even at an early age. The use of path analysis may provide important insights into the mechanisms and interactions of genetic and environmental effects that underly the childhood antecedents of atherosclerotic heart disease.

Common fragile site expression in lymphocytes from an individual mosaic for trisomy 8

During the course of a survey of fragile site expression in lymphocytes from twins one member of a dizygotic pair was found to be mosaic for trisomy 8. One hundred fifty metaphases from this individual were analyzed (100 treated with aphidicolin and 50 untreated); 43% were 46,XY and 57% 46,XY,+8. No differences were observed between the treated and control cultures in either the proportions of normal and trisomic metaphases or the overall or specific fragile site expression in the normal and trisomic cells.

Genetic factors that predispose the child to develop hypertension

Familial aggregation, population, and twin studies all point to important genetic influences on the level of blood pressure in childhood and adolescence. Whether a major gene effect operates during childhood has not been determined. The investigation of polygenic paths leads to the study of variables such as ion transport and reactivity paths that appear to be under strong genetic influences. The evidence suggests that abnormalities in these paths might be linked to a prehypertensive state. Univariate genetic analyses of systolic and diastolic blood pressure show that a significant portion of the variability of these variables is under genetic control. Moreover, during early adolescence, boys differ from girls in the regulation of their resting blood pressure. Multivariate genetic analyses show that in these young adolescents, genetic paths shared with body mass index appear to influence systolic but not diastolic blood pressure. The genetic relationship between systolic and diastolic blood pressure appears largely to be independent of body mass index. Genetic studies can partition the genetic and environmental influences on blood pressure and identify shared paths with variables previously believed to be linked epidemiologically. This information may have the capacity to be the framework for public health guidelines developed to lower the incidence of adult hypertension.

Multivariate genetic analysis of blood pressure and body size. The Medical College of Virginia Twin Study

BACKGROUND

In subjects of all ages, those who weigh the most often have the highest blood pressure. Thus, in epidemiological studies, weight is the most important correlate of blood pressure. Using the data from the Medical College of Virginia Twin Study, we asked these questions: 1) Do the same genetic paths that regulate body size also regulate systolic and diastolic blood pressure? 2) Are there distinct genetic pathways that regulate each of these variables? 3) Does environment play a major regulatory role? 4) Are the correlations among these variables mainly due to genetic or environmental effects? 5) Do genetic paths that regulate body size mediate the correlation between systolic blood pressure and diastolic blood pressure?

METHODS AND RESULTS

We ascertained 253 Caucasian twin pairs living in the Commonwealth of Virginia. The average age was 11.2 +/- 0.2 years. We used multivariate path analyses to investigate the genetic relations among systolic blood pressure, diastolic blood pressure, and body size. We found that there was a highly significant genetic relation between systolic blood pressure and body size and between systolic and diastolic blood pressure. There are genetic paths that are shared within these two sets of variables, but in each case, the paths for each pair appear to be separate from one another.

CONCLUSIONS

These analyses provide a method to partition correlation coefficients found in epidemiological studies into genetic and environmental components. The correlations found among these three variables are in large part due to these genetic relations. We found no genetic relation between diastolic blood pressure and body size.

Sex differences in the determinants of left ventricular mass in childhood. The Medical College of Virginia Twin Study

BACKGROUND

Left ventricular (LV) hypertrophy is a predictor of cardiovascular events in adults and has been observed in children and adolescents with hypertension. We wanted to establish the determinants of LV mass in normotensive preadolescent children. Our objectives were 1) to produce a simplified and generalizable model of the clinical variables that determine normal cardiac growth during childhood and 2) to understand better why males have an increased LV mass relative to females, even as children.

METHODS AND RESULTS

In a group of 243 eleven-year-old children, we analyzed anthropometric, hemodynamic, and echocardiographic data to define which variables were predictors of echocardiographically determined LV mass. Stepwise regression was used to predict LV mass overall, by sex, and by body size (body mass index). Overall, LV mass was directly related to weight, male sex, and systolic and diastolic blood pressure and inversely related to resting heart rate and skin-fold thicknesses. Systolic blood pressure was a determinant in boys but not in girls. Heart rate was a weak inverse correlate in both sexes. When the data were analyzed by body mass index quartile, weight was the sole predictor of LV mass in the largest children.

CONCLUSIONS

We conclude that in normotensive preadolescent children, 1) weight, but not pondersity, is a strong predictor of LV mass; 2) body fat is negatively associated with LV mass; 3) boys have an increased LV mass relative to girls; and 4) boys and girls have similar anthropometric determinants and may have different hemodynamic determinants. Our data suggest that body size, and in particular lean body mass, explains much of the variability in cardiac growth seen in children. The influence of hemodynamic variables seems to be more limited. Our findings are of general interest because, although hypertensive heart disease is well described, the early developmental stages are not well understood.

Aphidicolin-inducible common fragile-site expression: results from a population survey of twins

Common chromosomal fragile sites appear to be ubiquitous in humans and other mammals, and, although the molecular basis and function of these sites remain an enigma, it has been speculated that they may be a cytogenetic expression of gene activity. A population survey of 28 twin pairs was conducted to assess the heritability of common fragile-site expression. Our data yielded a heritability estimate of .88 for total site expression, suggesting that these sites may result from some common process that is under relatively stringent genetic control. An analysis of the expression of individual autosomal sites revealed that expression on both homologues in the same cell occurred more frequently than expected.

Blood pressure response to exercise. A marker for future hypertension?

Whether or not an exaggerated blood pressure response to exercise in childhood predicts adult-onset essential hypertension is not known. While peak systolic blood pressure during exercise can indicate future hypertension, left ventricular mass (measured echocardiographically) and resting systolic blood pressure seem to be much better predictors. However, the blood pressure response to exercise in groups of normotensive individuals, such as those with a family history of hypertension, may identify physiologic changes associated with the early hypertensive state.

Bivariate genetic analysis of left ventricular mass and weight in pubertal twins (the Medical College of Virginia twin study)

Left ventricular (LV) hypertrophy in adults is a recognized risk factor for the subsequent development of cardiovascular morbidity. To make informed preventive health decisions it is important to understand the interaction of genes and environment on LV mass. In both children and adults, weight is a strong correlate of LV mass. We hypothesized that genetic influences common to both of these variables could in part explain the strong relation between weight and LV mass in children. In a population of 341 twins (11 years old), these questions were asked: (1) How much of the total variance of LV mass is under genetic control? (2) After accounting for weight and weight adjusted for sexual maturity, how much of the remaining variance is genetic? (3) Of the total genetic variance, what proportion is specific for LV mass and what proportion is common to both weight and LV mass? (4) How much of the correlation between these 2 variables is explained by genes common to both LV mass and weight? Univariate genetic analyses documented that genes operating at different magnitudes in boys (63%) and girls (71%) explain a significant proportion of the variance of LV mass. After removing the effect of weight and sexual maturity by regression methods, genes remain an important influence. Bivariate genetic analyses confirmed that genes common to LV mass and weight significantly influence the covariation of these variables and that greater than 90% of the correlation of LV mass and weight is due to common genes.

Genetic and environmental contributions to cholesterol and its subfractions in 11-year-old twins. The Medical College of Virginia Twin Study

We conducted a cross-sectional analysis of the genetic and environmental contributions to the variance of lipoprotein cholesterol and its subfractions in children during early adolescence. Univariate path analysis was used to determine the relative contributions of genes, individual environment, and family environment to these measures in 233 11-year-old Caucasian twin pairs. For high density lipoprotein, high density lipoprotein2, low density lipoprotein, very low density lipoprotein, and triglycerides, a model that incorporated genes and individual environmental variation but not common environment was sufficient to explain the variation. Different magnitudes of genetic effects were seen for total cholesterol in boys and girls. High density lipoprotein3 showed different magnitudes by sex for genetic and individual environmental effect. Intermediate density lipoprotein was the only cholesterol subfraction in which shared, or common, environment was found to make a statistically significant contribution to the variation.