US Caucasians Research Articles

Heterozygote deficiency, population substructure and their implications in DNA fingerprinting

Substructured populations exhibit an overall deficiency of heterozygosity whose proportional magnitude depends on the nature of substructuring, i.e., the number of subpopulations (s), their time of divergence (t) from the ancestral population, and the rate of gene flow amongst them (m). Since apparent heterozygote deficiency could be caused by many factors other than population substructuring, one must examine the nature of substructuring that could produce the observed extent of heterozygote deficiency, in order to infer the substructuring from an observed heterozygote deficiency. Using the equivalence of proportional heterozygote deficiency and the coefficient of gene differentiation (GST), we can generate isolines of GST as functions of s, t (in units of 2Ne generations, Ne being the effective population size) and m. Analytical results suggest that large GST values cannot be reached by substructuring alone, unless the number of subpopulations are large and they remain isolated over a long period of time. Application of the theory to population data on six variable number of tandem repeats (VNTR) loci in US Caucasians and US Blacks demonstrates that the observed heterozygote deficiencies at these loci cannot be explained by substructuring within these populations alone. This is so because such large values of GST (3%-10%) would require an absence of gene exchange between the subpopulations and a divergence time from each other of at least 25,000 years ago, neither of which is compatible with the demography and ethnohistory of US Caucasians and Blacks. In contrast, the inability to detect extreme-sized alleles and/or incomplete resolution of nearly similar-sized alleles following Southern gel electrophoresis could easily explain the observed heterozygote deficiencies. The implications of these results are discussed in the context of the forensic use of DNA-typing data, and justify the employment of population genetic principles in forensic genetics.

Apparent heterozygote deficiencies observed in DNA typing data and their implications in forensic applications.

Restriction fragment length polymorphisms (RFLP) analysis using the Southern blot technique can be used to recognize copy number variation of variable number of tandem repeats (VNTR) of conserved core sequences at several regions of the human genome. This new class of polymorphisms reveals a high degree of genetic variation, useful for individual identification purposes. Criticisms against forensic applications of such DNA typing data include the limitation of employing Hardy-Weinberg expectation of genotype frequencies, since several surveys indicate apparent deficiency of heterozygosity (or excess homozygosity) in comparison with Hardy-Weinberg expectations. This research postulates an alternative explanation of deficiency of apparent heterozygosity which is caused by the inability to detect extremely small-sized alleles (called 'non-detectable' alleles) due to the sensitivity of Southern gel electrophoresis. We show that the presence of 'non-detectable' alleles can produce pseudo-homozygosity and their frequencies can be predicted from the observed proportional heterozygote deficiency. Furthermore, in the covert presence of such 'non-detectable' alleles, we show that the gene-count method provides over-estimates of allele frequencies in the sample population, and hence the Hardy-Weinberg predictions of genotype frequencies avoid wrongful bias against suspects in forensic applications of DNA typing data. Applications of this theory to population data on six VNTR loci in US Caucasians and US Blacks suggest that the presence of 'non-detectable' alleles could be the major cause of apparent heterozygote deficiency, and the current approaches of predicting the population frequency of specific DNA phenotypes are practically free of the possible wrongful bias in courtroom applications of DNA typing data.

Effects of polymorphisms in apolipoproteins E, A-IV, and H on quantitative traits related to risk for cardiovascular disease.

The impact of the common alleles at structural loci coding for apolipoprotein (apos) A-IV, E, and H on 12 quantitative risk factors for cardiovascular disease (apos A-I, A-II, B, C-II, C-III, and E; total cholesterol; triglycerides; high density lipoprotein cholesterol; systolic blood pressure; diastolic blood pressure; and red blood cell sodium-lithium countertransport) was estimated in 453 unrelated individuals (227 men and 226 women) aged 26-63 years from the Rochester Family Heart Study, who were not using medications affecting lipid levels or blood pressure. Each risk factor was adjusted for concomitants (assay date, age, age, squared, height, weight and smoking status) before the genotypic effects on mean levels and variances were estimated. Allele frequencies were the same in men and women and were similar to those observed in other studies of US Caucasians. There were very different gender-specific estimates of the relative contribution of concomitants, measured genetic effects, and residual unexplained effects to the interindividual variation of particular traits. Allelic variation in apo E had effects on the greatest number of traits, namely apo E, apo B, apo C-II, and total cholesterol. An effect on triglycerides was dependent on the inclusion of hypertriglyceridemic subjects. Allelic effects of apo A-IV and apo H were much less than those estimated for the apo E polymorphism. A possible role for apo H in high density lipoprotein metabolism is suggested. This study indicates that variation in many genes may influence variation in a particular trait and that a particular gene may have pleiotropic effects on several traits.

Hypertension in African-Americans.

A considerable disparity exists between African-Americans and US Caucasians in the incidence, severity, and management of hypertension. As a consequence, overall hypertension-related morbidity and mortality rates are at least threefold to fivefold higher in African-Americans than in Caucasians. Alarmingly high frequencies of stroke, end-stage renal disease, congestive heart failure, and left ventricular hypertrophy occur in African-Americans. To bring this crisis under control will require a renewed commitment to expanded research, improved public health measures, and more effective clinical intervention. Current hypertension control programs must be expanded and adequately funded. In addition, primary prevention of hypertension should be strongly recommended for the US population, especially African-Americans.

Coronary artery disease in African-Americans.

Contrary to opinions generally accepted in the past, CHD is very common in both African-American men and women, with incidence rates approaching those of US Caucasians. Higher prevalence of hypertension, diabetes, cigarette smoking, and obesity all contribute to the high level of CHD in African-Americans. Additional research is needed about the interrelations and management of various risk factors for CHD in African-Americans outside of the sudden death of African-Americans outside of the hospital is urgent, and special attention should be given to accessibility and use of health services by minority populations.

Quantitative computed tomography of lumbar vertebrae in Japanese patients with osteoporosis

Vertebral trabecular bone mineral density of both healthy Japanese subjects and Japanese patients with osteoporosis was measured by quantitative computed tomography (QCT) technique. The age-related reduction rate in vertebral trabecular bone mineral density of control females averaged 1.1% per year, from age 20 to 80, with an accelerated loss demonstrated after age 40. In the male controls, trabecular bone mineral density declined by an average of 0.9% per year. These values were found to be similar to the University of California at San Francisco (UCSF) QCT data (US Caucasians: 1.2% for female, 0.72% for male). Therefore, it appears that age-related rates of trabecular bone loss in the lumbar vertebrae may be similar for both Japanese and Caucasians. However, when compared to average values in UCSF QCT data of comparable age and sex, the mean values in Japanese appear to be approximately 10–20 mg/cm 3 lower than Caucasian counterparts. All female patients with osteoporosis as evidenced by atraumatic vertebral fracture had QCT values below 50 mg/cm 3. It is suggested that the Japanese may have lower trabecular bone mineral density than Caucasians but may also have a lower threshold for fracture of the vertebrae, Further studies are needed to establish the possible racial differences in vertebral trabecular bone mineral density, and to determine whether these possible disparities are related to genetic differences, or to differences in body size, dietary intake, physical activity or other lifestyle/environmental factors.

Epidemiology of endometrial cancer.

This review of endometrial cancer summarizes the demographic characteristics of patients with the disease, their hormonal risk factors related to endogenous and exogenous estrogens and medical history, and other risk factors. Endometrial cancer increased in incidence in the US in the early 1970s, but then declined again in the last 2 decades. Possible reasons are classification including estrogen- induced hyperplasia, but also increased use of exogenous estrogens primarily in post-menopausal women, who are the predominant victims. Postmenopausal estrogen usage decreased at the same time. The highest incidence occurs in Polynesian women, although US Caucasians have more endometrial cancer then Blacks or European women. Endometrial cancer is common in women with estrogen-secreting ovarian cancer. Women with polycystic ovaries, where the steroid androstenedione is secreted and converted to estrone in peripheral tissues, but progesterone is lacking, are higher risk for endometrial hyperplasia and cancer. Obese women are also at risk (estimated 20-fold), as they have low sex binding globulin and higher estrogen levels. Any exogenous estrogen, by any route, even if stopped for a week per month confers higher risk for endometrial cancer, as shown by virtually all case control studies. Very little data exists on the actual effect of taking progestins with postmenopausal estrogens. These tumors are less invasive, more differentiated, and often detected earlier than non-estrogen dependent endometrial cancers. Other putative risk factors, e.g., diabetes, hypertension, gall bladder disease, radiation exposure, and family history of breast cancer have no solid evidence for association. Smoking, however, is associated with a lower risk of endometrial cancer.

Genetic studies of low-abundance human plasma proteins. XII. A new variant of corticosteroid-binding globulin detected by isoelectric focusing/immunoblotting.

Thin-layer polyacrylamide gel isoelectric focusing over the pH range 3.5-5 followed by immunoblotting was used to investigate the occurrence and frequency of genetic variation in corticosteroid-binding globulin (CBG). Plasma samples from US Caucasians (n = 105) and US Blacks (n = 106) from Pittsburgh, Pa., Canadian Indians from Vancouver Island (n = 91) and Nigerian Blacks (n = 116) were analyzed. A complex isoprotein pattern was observed in all individuals tested. Reduction of this pattern to a single primary band following neuraminidase treatment indicates that the observed intraindividual variation is due to variation in the number of sialic acid residues associated with CBG. The CBG variant pattern consisted of a series of isoprotein bands having the same mobility as the common pattern, and a second series of bands at a more acidic isoelectric point. This pattern is consistent with heterozygosity for a rare CBG allele.