Molecular epidemiology: the impact of molecular biology in epidemiology research.

Progress in molecular biology and genetics is changing the practice of medicine and public health through the development of molecular diagnostics and targeted interventions for susceptible individuals. The ethical, legal and social issues that are becoming apparent as these important discoveries are introduced into practice will have an enormous impact on society. The accurate translation of this new genetic information from the laboratory to the community is an urgent need. Molecular epidemiology is at the foundation of this important link, and represents the scientific basis of public health for the 21st Century.

Insulin-dependent diabetes mellitus, physical activity, and death.

The beneficial effect of physical activity in the general population is well known, but, to the authors' knowledge, has not been reported for persons with insulin-dependent diabetes mellitus. In a cohort of 548 diabetes patients followed as part of the Pittsburgh Insulin-dependent Diabetes Mellitus Morbidity and Mortality Study, physical activity was ascertained by survey in 1981, and mortality was ascertained through January 1, 1988. Cases were also compared with non-diabetic sibling controls. Activity level among cases varied inversely with the occurrence of diabetic complications. Overall activity level was inversely related to mortality risk. Sedentary males (< 1,000 kcal/week) were three times more likely to die than active males (> 2,000 kcal/week). A similar, but statistically nonsignificant, relation was seen in females. Cox proportional hazards analysis controlling for potential confounders (age, body mass index, insulin dose, reported diabetes complications, cigarette smoking, and current alcohol drinking) similarly revealed that activity level was inversely associated with mortality risk. Comparison of cases with non-diabetic sibling controls identified similar activity levels for the two groups. The results suggest that activity is not detrimental with regard to mortality, and may in fact provide a beneficial effect in terms of longevity in diabetes patients.

Autoimmunity and genetics contribute to the risk of insulin-dependent diabetes mellitus in families: islet cell antibodies and HLA DQ heterodimers.

The risk for insulin-dependent diabetes mellitus (IDDM) associated with genetic susceptibility markers at the human leukocyte antigen (HLA) DQA1 and DQB1 loci was evaluated among individuals with and those without islet cell antibodies. A total of 108 antibody-positive parents and siblings of IDDM patients from the Pittsburgh registry were identified among 1,592 who were screened. HLA-DQ molecular typing was performed on 79 of these individuals and on 78 antibody-negative relatives. There were similar proportions of homozygotes for both of the diabetogenic alleles DQA1 arginine-52 (R/R) and DQB1 non-aspartate-57 (nD/nD) among the antibody-positive and antibody-negative relatives (19.0 and 15.4%, respectively). However, subsequent development of IDDM was restricted to individuals who were both antibody positive and carried the potential to make at least one diabetogenic DQ heterodimer. A dose-response effect was observed among the antibody-positive relatives, in which two of 18 capable of generating one diabetogenic heterodimer and six of 29 generating two heterodimers became insulin requiring. Nine of 15 who were homozygous for both R/R and nD/nD, coding exclusively for diabetogenic variants, became diabetic over the course of the follow-up. With a multivariate model, the relative risk for IDDM among those with islet cell antibodies who were also R/R and nD/nD was estimated to be 229.3 compared with those lacking both, after age and sex were controlled for. The data suggest that while autoimmunity, indicated by the presence of cytoplasmic islet cell antibodies may be relatively common, it progresses only in those with variant HLA-DQ molecules.

Cardiovascular disease and arterial calcification in insulin-dependent diabetes mellitus: interrelations and risk factor profiles. Pittsburgh Epidemiology of Diabetes Complications Study-V.

Cardiovascular disease is a frequent complication of insulin-dependent diabetes mellitus (IDDM), but the prevalence, interrelations, and risk factors of its principal components (coronary, cerebrovascular, and lower-extremity arterial disease) and of medial arterial wall calcification are not well understood. To address these issues, data from the Epidemiology of Diabetes Complications Study (n = 657) baseline examination were examined. The term coronary heart disease (CHD) was applied to those with myocardial infarction or angina, whereas lower-extremity arterial disease (LEAD) was applied to those who had undergone amputation of a lower limb or who had an ankle to arm blood pressure ratio less than 0.8 at rest or after exercise. Calcification of the lower-extremity arteries was considered to be present if ankle pressure was more than 100 mm Hg higher than brachial pressure. Although the prevalence of CHD was low, LEAD was significantly more common in women than in men (p less than 0.01), whereas calcification was more frequent in men than in women (p less than 0.01). Ten percent of those with LEAD also had CHD, and 8% with LEAD had calcification. Modeling of potential risk factors (e.g., diabetes duration and glycosylated hemoglobin) revealed that duration, female gender, fibrinogen, low density lipoprotein cholesterol, high density lipoprotein cholesterol, and high density lipoprotein cholesterol to apolipoprotein A-I ratio were independent predictors of LEAD, whereas for CHD only, diabetes duration and hypertension contributed to CHD. Calcification revealed a mixed pattern, with duration, hypertension, and triglyceride to apolipoprotein A-I ratio being the statistically significant associated factors. The results suggest that although LEAD, CHD, and calcification often coexist, their risk factor profiles differ.

Human insulin use and hypoglycaemia: insights from the Pittsburgh Epidemiology of Diabetes Complications Study.

Recently, concern has arisen that human (as opposed to beef or pork) insulin may cause more frequent and/or severe hypoglycaemia in association with reduced warning symptoms. This question was examined from questionnaire data of 628 Type 1 diabetic patients (mean age 28 years and duration of diabetes 19 years) participating in the baseline examination of a follow-up study of diabetes complications. Those using human insulin (n = 73) reported an insignificantly higher frequency of hypoglycaemic reactions in the last year than those using animal insulin (66 vs 55% with reactions at least monthly) and only a weak trend was seen overall for the prevalence of human insulin use to increase with increasing frequency of hypoglycaemia (p = 0.06). Hypoglycaemic reactions resulting in unconsciousness were too rare to permit analysis by type of insulin used. The prevalence of reduced awareness of hypoglycaemia was similar among human insulin users to that seen in animal insulin users (25 vs 19%, NS). However, prevalence of reduced awareness showed a strong relationship to current blood glucose in the animal (r = -0.18, p less than 0.001) but not human (r = -0.06, NS) insulin users. Excluding patients with autonomic symptoms or neuropathy did not alter the results, nor did excluding the 34 individuals taking more than three insulin injections per day. It is concluded that human insulin use is not associated with either any substantial increased frequency of hypoglycaemia or reduction in awareness of hypoglycaemia. However, human insulin use does appear to be associated with reduced awareness of hypoglycaemia in those whose blood glucose control is relatively poor.

Measuring subclinical neuropathy: does it relate to clinical neuropathy? Pittsburgh epidemiology of diabetes complications study-V.

We report results from 120 (25- to 34-year-old) participants in a neuropathy substudy of subjects with insulin-dependent diabetes mellitus (IDDM) taking part in a cohort follow-up study. Diabetic neuropathy was evaluated by quantitative sensory testing, nerve conduction studies, and clinical examination. Mean quantitative sensory thresholds differed significantly by clinical category of abnormal sensation and ankle reflex activity. Mean sural and peroneal amplitudes and conduction velocities were also significantly lower for subjects classified as having abnormal ankle reflex activity. Modeling potential correlates in logistic analyses showed glycemic control, triglyceride levels, and hypertension status to be independently associated with clinically overt neuropathy. Similar lipid and hemodynamic parameters were associated with abnormality by any single assessment method used to define neuropathy. Although follow-up is needed to resolve the best assessment methods for determining neuropathy, these results suggest that good glycemic control as well as control of blood pressure and lipids is advisible.

Prevalence of complications in IDDM by sex and duration. Pittsburgh Epidemiology of Diabetes Complications Study II.

The prevalence of and interrelationships among all four major complications of insulin-dependent diabetes mellitus (IDDM) and their risk factors are being examined in a large epidemiologic study of IDDM subjects diagnosed in childhood. This article focuses on the baseline prevalence of complications in the 657 subjects diagnosed between 1950 and 1980 and currently aged 8-48 yr, with a mean duration of 20 yr. In addition to background retinopathy being virtually universal after 20 yr of diabetes, proliferative retinopathy affects 70% of IDDM subjects after 30 yr duration. As with overt nephropathy, prevalence of proliferative retinopathy is marginally higher in females than in males at short durations; the previously reported male excess is limited to the subjects with IDDM of longer duration (greater than or equal to 25 yr). Somewhat different patterns of microalbuminuria are also seen by sex. Males show a threefold increase in prevalence from 10 to 25 yr duration, whereas females show a more constant prevalence across these durations. A further rise in microalbuminuria is seen in males but not females at greater than or equal to 30 yr duration, giving a combined prevalence of microalbuminuria and overt nephropathy at greater than or equal to 30 yr duration of 84% (males) and 59% (females). Distal symmetrical polyneuropathy shows a constant rise with duration and is only marginally higher in men. Prevalence of cardiovascular (coronary and cerebral) disease shows no sex difference, whereas peripheral vascular disease is particularly common in women after 30 yr duration (greater than 30%) compared with men (11%) when determined by ankle/arm blood pressure ratio less than 0.8 at rest or after exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Diabetic autonomic neuropathy and cardiovascular risk. Pittsburgh Epidemiology of Diabetes Complications Study III.

Diabetic autonomic neuropathy (DAN) has been shown to confer a high risk of mortality. The association between DAN and cardiovascular risk factors was examined in a well-defined cohort of 25- to 34-year-old insulin-dependent diabetes mellitus subjects (n = 168) with and without DAN as evaluated by heart rate response to deep breathing, standing, and the Valsalva maneuver. The autonomic tests were performed using both an office-based procedure and a method employed by the Diabetes Control and Complications Trial with analyses performed by the Diabetes Research and Analysis Association, Lexington, Ky. Good agreement was found between the procedures for the assessment modalities of heart rate response to deep breathing. Modeling potential correlates in logistic analyses, where heart rate response to deep breathing was the dependent variable, revealed hypertension status, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and gender (female) to be independent determinants of DAN. These results suggest that traditional cardiovascular risk factors are important correlates of DAN and may relate to both its cause and poor prognosis. Since these results are from a cross-sectional study, prospective follow-up of this cohort will be needed for confirmation.

Epidemiological correlates of diabetic neuropathy. Report from Pittsburgh Epidemiology of Diabetes Complications Study.

The natural history of diabetic neuropathy and its risk factors are not well understood, apart from the recognition that prevalence increases with duration and, in many studies, degree of glycemia. The role of potential risk factors was therefore evaluated in a cross-sectional analysis from the baseline examination of the Pittsburgh Epidemiology of Diabetes Complications Study. We present results from the first 400 subjects seen at baseline examination. Neuropathy was determined by a trained internist with a standardized examination and was defined as the presence of at least two of three criteria: abnormal sensory or motor signs, symptoms consistent with neuropathy, and decreased tendon reflexes. The prevalence of neuropathy in this cohort was 34% (18%, 18-29 yr old, 58% greater than or equal to 30 yr old) with no difference by sex. By focusing on subjects greater than or equal to 18 yr old, all significant univariate variables (e.g., duration, glycosylated hemoglobin [HbA1]) were analyzed in 3 multiple logistic regression models: all subjects greater than or equal to 18 yr old and separating the same subjects into two groups based on age (18-29 and greater than or equal to 30 yr). Duration, HbA1, smoking status, and high-density lipoprotein cholesterol were found to be associated with neuropathy in the models for the greater than or equal to 18-yr-old group and the greater than or equal to 30-yr-old group. In the 18- to 29-yr-old group, duration, HbA1, and hypertension status were found to be significantly associated with neuropathy.(ABSTRACT TRUNCATED AT 250 WORDS)

Aspartic acid at position 57 of the HLA-DQ beta chain protects against type I diabetes: a family study.

One hundred seventy-two members from 27 randomly selected multiple case Caucasian families of patients with insulin-dependent diabetes mellitus (IDDM) were studied at the DNA level to ascertain the reliability of codon 57 of the HLA-DQ beta-chain gene as a disease protection/susceptibility marker. The analysis was carried out by polymerase chain reaction amplification of DNA encoding the first domain of the DQ beta chain and by dot blot analysis of the amplified material with allele-specific oligonucleotide probes. One hundred twenty-three randomly selected healthy Caucasian donors were also tested. The results demonstrated that haplotypes carrying an aspartic acid in position 57 (Asp-57) of their DQ beta chain were significantly increased in frequency among nondiabetic haplotypes (23/38), while non-Asp-57 haplotypes were significantly increased in frequency among diabetic haplotypes (65/69). Ninety-six percent of the diabetic probands in our study were homozygous non-Asp/non-Asp as compared to 19.5% of healthy unrelated controls. This conferred a relative risk of 107 (chi 2 = 54.97; P = 0.00003) for non-Asp-57 homozygous individuals. Even though the inheritance and genetic features of IDDM are complex and are not necessarily fully explained by DQ beta chain polymorphism, this approach is much more sensitive than HLA serolog in assessing risk for IDDM.