DRB1*04 and DQ alleles: expression of 21-hydroxylase autoantibodies and risk of progression to Addison's disease

Of 957 patients with type 1 diabetes without known Addison's disease 1.6% (n = 15) were positive for 21-hydroxylase autoantibodies. Among DQ8/DQ2 heterozygous patients, the percentage expressing 21-hydroxylase autoantibodies was 5% (10 of 208) vs. less than 0.5% of patients with neither DQ8 nor DQ2. Three of the diabetic patients found to have 21-hydroxylase autoantibodies on screening were subsequently diagnosed with Addison's disease. Overall, the genotype DQ8/DQ2, consisting of DRB1*0404/DQ8 with DRB1*0301/DQ2, was present in 14 of 21 patients with Addison's disease (8 of 12 with diabetes and 6 of 9 without diabetes or antiislet autoantibodies) vs. 0.7% of the general population (109 of 15,547; P < 10(-6)) and 11% of patients with DM without Addison's disease (62 of 578; P < 10(-6)). Among patients with diabetes with DQ8, Addison's disease was strongly associated with the specific DRB1 subtype, DRB1*0404 (8 of 9 patients from 8 families, in contrast to only 109 of 408 DQ8 DM patients with diabetes without Addison's disease having DRB1*0404; P < 0.001). Among 21-hydroxylase autoantibody-positive DQ8 patients, 80% with DRB1*0404 (12 of 15) had Addison's disease, in contrast to 1 of 10 autoantibody-positive patients with DRB1*0401 or DRB1*0402 (P < 0.001). We conclude that patients with DRB1*0404 and 21-hydroxylase autoantibodies are at high risk for Addison's disease. Patients with DRB1*0401 and DRB1*0402 have more limited progression to Addison's disease despite the presence of 21-hydroxylase autoantibodies.

Definition of multiple ICA512/phogrin autoantibody epitopes and detection of intramolecular epitope spreading in relatives of patients with type 1 diabetes

The related tyrosine phosphatase-like proteins, islet cell antigen 512 (ICA512) and phosphatase homologue in granules of insulinoma (phogrin), are major targets of autoantibodies in patients with type 1 diabetes. In the current study, we have examined the overlapping specificities and antigenic epitopes of autoantibodies to ICA512 and phogrin and determined whether intramolecular epitope spreading occurs during the development of diabetic autoimmunity. ICA512 autoantibodies and phogrin autoantibodies were detected in 65-70% (n = 110) of patients with new-onset type 1 diabetes and 60-65% (n = 42) of prediabetic relatives of patients with type 1 diabetes. Of the sera, 10% reacted with ICA512 but not phogrin, whereas only 1% of sera reacted with phogrin but not ICA512. The binding of phogrin autoantibodies in 88 dual (ICA512 and phogrin) autoantibody-positive sera could be completely blocked by excess recombinant ICA512, whereas the blocking of ICA512 autoantibodies with recombinant phogrin was only partial (mean inhibition of 58.9 +/- 3.7%, mean +/- SE). Binding and competition analysis using multiple chimeric ICA512/phogrin constructs demonstrated that a major unique epitope for ICA512 autoantibodies is localized to amino acids 762-887. A conformational epitope associated with the carboxy-terminal 31 amino acids of ICA512 was recognized by one-third of sera, and a minor epitope is located on amino acids 601-762 of ICA512. The major epitopes for phogrin-selective autoantibodies were localized to amino acids 640-922 of phogrin. Sequential serum samples were analyzed in 22 relatives who expressed ICA512/phogrin autoantibodies. Intramolecular epitope spreading was found for 5 of 13 relatives who have progressed to type 1 diabetes. Among nine relatives who have remained nondiabetic, three demonstrated a decrease in the number of epitopes recognized. These studies highlight the complexity of autoantibody recognition of ICA512/phogrin and are consistent with the hypothesis that ICA512/phogrin may be recognized as a consequence of beta-cell destruction.

Intensity and amount of physical activity in relation to insulin sensitivity: the Insulin Resistance Atherosclerosis Study

CONTEXT

Exercise training is associated with improved insulin sensitivity (SI), but the potential impact of habitual, nonvigorous activity is uncertain.

OBJECTIVE

To determine whether habitual, nonvigorous physical activity, as well as vigorous and overall activity, is associated with better SI.

DESIGN

A multicultural epidemiologic study.

SETTING

The Insulin Resistance Atherosclerosis Study, conducted in Oakland, Calif; Los Angeles, Calif; the San Luis Valley, Colo; and San Antonio, Tex.

PARTICIPANTS

A total of 1467 men and women of African American, Hispanic, and non-Hispanic white ethnicity, aged 40 to 69 years, with glucose tolerance ranging from normal to mild non-insulin-dependent diabetes mellitus.

MAIN OUTCOME MEASURE

Insulin sensitivity as measured by an intravenous glucose tolerance test.

RESULTS

The mean SI for individuals who participated in vigorous activity 5 or more times per week was 1.59 min(-1) x microU(-1) x mL(-1) x 10(-4) (95% confidence interval [CI], 1.39-1.79) compared with 0.90 (95% CI, 0.83-0.97) for those who rarely or never participated in vigorous activity, after adjusting for potential confounders (P<.001). When habitual physical activity (estimated energy expenditure [EEE]) was assessed by 1-year recall of activities, the correlation coefficient between SI and total EEE was 0.14 (P<.001). After adjustment for confounders, vigorous and nonvigorous levels of EEE (metabolic equivalent levels > or = 6.0 and <6.0, respectively) were each positively and independently associated with SI (P< or =.01 for each). The association was attenuated after adjustment for the potential mediators, body mass index (a measure of weight in kilograms divided by the square of the height in meters), and waist-to-hip ratio. Results were similar for subgroups of sex, ethnicity, and diabetes.

CONCLUSIONS

Increased participation in nonvigorous as well as overall and vigorous physical activity was associated with significantly higher SI. These findings lend further support to current public health recommendations for increased moderate-intensity physical activity on most days.

Dietary fat and insulin sensitivity in a triethnic population: the role of obesity. The Insulin Resistance Atherosclerosis Study (IRAS)

From the Insulin Resistance Atherosclerosis Study (IRAS), 1173 men and women of African-American, non-Hispanic white, and Hispanic ethnicity with no history of diabetes were included in an evaluation of the cross-sectional relation of habitual dietary fat intake with insulin sensitivity (SI) as assessed by minimal-model analysis of a 12-sample, insulin-modified frequently sampled intravenous-glucose-tolerance test. Dietary intake was measured by a food-frequency interview modified to enhance sensitivity to food choices within the three ethnic groups. Percentage of energy from total fat was associated with rank of SI (SI(rank); r = -0.06, P = 0.03), with log fasting insulin (r = 0.10, P < 0.001), and with BMI (r = 0.10, P < 0.001). Multiple-linear-regression models included SI(rank) as the dependent variable, dietary fat (g/d) as the primary independent variable adjusted sequentially for total energy, other covariates, body mass index, and waist-hip circumference ratio (WHR). For all subjects combined, total fat intake was inversely related to SI(rank), but this association was not significant (P = 0.14) and was attenuated by adjustment for body mass index and WHR (P = 0.44). The association of total fat (g/d) with SI(rank) differed significantly (P < 0.01) for obese compared with nonobese individuals. Higher fat intake was associated with lower SI(rank) among obese (beta = -1.40, P = 0.03) but not among nonobese persons (beta = 0.16, P = 0.80). Among the obese (body mass index < or = 63), adjustment for body mass index largely accounted for the observed association of dietary fat with SI(rank). These findings were generally consistent for monounsaturated, polyunsaturated, and saturated fats. Among individuals already at increased risk for non-insulin-dependent diabetes mellitus because of obesity, high intake of dietary fat may worsen insulin sensitivity. This effect may be mediated by the relation of dietary fat to obesity.

The design of trials for prevention of IDDM

Several large clinical trials for the prevention of IDDM in islet cell antibody positive first-degree relatives are planned or underway. The design of these trials rests in part on assumptions about the natural history of autoimmunity during the prediabetic period and on the likely effectiveness of the intervention being tested. At this time, most of the factors that influence the required sample size can only be roughly estimated.

Early exposure to cow's milk and solid foods in infancy, genetic predisposition, and risk of IDDM

Using a case-control study design, we examined the hypothesis that early exposure to cow's milk and solid foods increased the risk of IDDM. An infant diet history was collected from 164 IDDM subjects from the Colorado IDDM Registry with a mean birth year of 1973, and 145 nondiabetic population control subjects who were frequency matched to diabetic subjects on age, sex, and ethnicity. Early exposure was defined as exposure occurring before 3 mo of age. After controlling for ethnicity, birth order, and family income, more diabetic subjects were exposed early to cow's milk (OR 4.5, 95% CI 0.9-21.4) and solid foods (OR 2.5, CI 1.4-4.3) than control subjects. To examine this association while accounting for the genetic susceptibility to IDDM, we defined individuals as high and low risk by an HLA-DQB1 molecular marker. Early exposure to cow's milk was not associated with elevated risk for IDDM in low-risk individuals. Relative to unexposed low-risk individuals, early exposure to cow's milk was strongly associated in individuals with a high risK marker (OR 11.3, CI 1.2-102.0). Similar findings were observed for early exposure to solid foods. These data indicate that early exposure to cow's milk and solid foods may be associated with increased risk of IDDM. The inclusion of HLA-encoded risk in the analyses demonstrates the combined effect of genetic and environmental factors.

Incidence of insulin-dependent diabetes mellitus in Colorado

We examined the incidence of insulin-dependent diabetes mellitus in children 0-17 years of age in Colorado from 1978 to 1988. Cases were ascertained from a statewide registry based on physician surveillance. A total of 1,376 children were diagnosed during this interval in a population averaging 860,000 children. The degree of ascertainment was estimated to be 93.3%. The age-adjusted incidence rate of insulin-dependent diabetes mellitus was 14.8/100,000 person-years. The rate was lower in individuals of Spanish origin (Hispanics) (8.7/100,000 person-years) compared with non-Hispanic individuals (15.5/100,000 person-years) (incidence rate ratio = 0.6, 95% confidence interval = 0.4-0.8). Incidence rates were higher in winter and lower in summer for children 5-17 years old. Children diagnosed before the age of 5 years showed no significant seasonal pattern, although peak incidences were observed in autumn and spring. No temporal trend in diabetes incidence was observed overall or by ethnic group. The increasing insulin-dependent diabetes incidence reported by registries in Europe during this time period was not observed in Colorado.