A.G. Cudworth

EVIDENCE FOR A LONG PREDIABETIC PERIOD IN TYPE I (INSULIN-DEPENDENT) DIABETES MELLITUS

In a prospective investigation of the prediabetic period before onset of type 1 (insulin-dependent) diabetes, HLA genotypes were determined in 582 healthy parents and siblings of 160 affected children. Islet cell antibody was sought by both the conventional (ICA-IgG) and the complement fixation (CF-ICA) techniques during regular prospective observation over a mean period of 2.0 years. 4 siblings and 2 parents became diabetic; the interval before detection of any biochemical abnormality exceeded a year in 4 of these (range 3-30 months), and in all cases ICA-IgG was positive from the outset, CF-ICA being positive in 5. These observations suggest that the initiation of pathogenesis may precede the abrupt clinical onset of diabetes by several years, even in children. This has important implications, both for research and for possible future prophylaxis.

COMPLEMENT-FIXING ISLET-CELL ANTIBODIES IN TYPE-I DIABETES: POSSIBLE MONITORS OF ACTIVE BETA-CELL DAMAGE

Evidence is presented for the existence of a separate species of islet-cell antibodies which fix complement. Investigations in type I diabetics, non-diabetic polyendocrine patients, and unaffected first-degree relatives of type I diabetic probands show that the complement-fixing islet-cell antibodies are more closely related to the onset of clinical disease than the conventional islet-cell antibody, and they tend to disappear more rapidly. The complement-fixing antibodies may reflect damage of pancreatic beta cells more selectively and may be preferable to the conventional antibody as a serological marker for studying the natural history of type I diabetes.

The genetic susceptibility to type 1 (insulin-dependent) diabetes: Analysis of the HLA-DR association

SummaryHLA-DR and MT1, MT2, MT3 genotypes have been investigated in 123 Type 1 (insulin-dependent) diabetic subjects and their families. Ninety-eight percent of probands possessed either DR3 (relative risk = 5.0), or DR4 (relative risk = 6.8) or both antigens (relative risk = 14.3), emphasizing the strong association of the disease with these two antigens. Almost 51% of the probands were DR3, DR4 heterozygotes. The DR antigen combinations of the parents leading to DR3, DR4 heterozygous and to DR3 and DR4 homozygous offspring were analysed. There was a marked increase in DR3, DR4 heterozygosity, but no increase in homozygosity for these antigens compared with the expected frequencies. These results are compatible with the existence of two susceptibility genes operating at a locus or at loci closely linked to that of HLA-DR. There was a striking reduction of DR7 (relative risk = 0.1) and only five probands possessed DR2 (relative risk = 0.1). In each case, the other inherited allele was DR3 or DR4. Linkage disequilibrium between B7 and DR2 was much lower in the haplotypes of the probands than in the ‘non-diabetic’ parental haplotype. In contrast, the association of BW62 with DR4 was more pronounced in the haplotypes of the probands. There was no increase in recombination frequency in these families and no strong effect of HLA-DR on age of onset could be demonstrated. There was a significant shift towards DR identity compared with identity for the whole HLA haplotype (A, B, C and DR) in both healthy and diabetic siblings (p < 0.025).

Can Future Type I Diabetes Be Predicted? A Study in Families of Affected Children

This article examines the risk of type I (insulin-dependent) diabetes in siblings of affected children, in relation to HLA genotypes. The 288 available siblings of 160 diabetic probands were grouped according to the number of HLA haplotypes in common with their probands. HLA-identical siblings (both haplotypes in common) have an approximately 100 times greater risk of developing the disease than that in the general population, and this risk is significantly higher than that in haplo-identical siblings (one haplotype in common) P = 0.008). Thus, in Northern European populations, some 30% of HLA-identical siblings are expected to be diabetic by the age of 30 yr. The risk in nonidentical siblings (neither haplotype in common) is not significantly increased. These findings carry implications for genetic counseling and research.

EVIDENCE FOR RAISED K-CELL LEVELS IN TYPE-I DIABETES

The proportion of blood mononuclear cells forming low-affinity rosettes with sheep erythrocytes (K cells) was abnormally high in 13 (57%) of 23 children with classical type-1 diabetes at diagnosis but normal in children who had had diabetes for more than a year. A raised proportion of K cells was also found in 5 out of 10 unaffected siblings with islet-cell antibodies and at least one HLA haplotype in common with the diabetic proband; and in 10 (45%) of 22 subjects with type-1 diabetes and co-existent autoimmune thyroid disease irrespective of the duration of diabetes or the presence of islet-cell antibodies. These findings may be new evidence for lymphocyte-mediated beta-cell destruction and support the idea of immunogenetic heterogeneity within type-1 diabetes.

Risk Factors Associated with Severe Proliferative Retinopathy in Insulin-dependent Diabetes Mellitus

The natural history of disease and suspected risk factors for bad prognosis were investigated in 40 subjects with insulin-dependent diabetes mellitus who had severe retinopathy and in 22 patients with a similar duration of diabetes without evidence of complications. The retinopathy group showed a marked excess of men (ratio 2:1). Examination of the data in the literature also showed a striking excess of men, 61% (P < 0.001) in patients with insulin-dependent diabetes and severe microvascular disease. In addition, proliferative retinopathy was found to have significant associations with current poor diabetic control, hypertension, and previous treatment with once-daily insulin regimens, particularly with protamine zinc insulin.

Genetic and Immunologic Factors in Microvascular Disease in Type I Insulin-Dependent Diabetes

A detailed study of 133 subjects with insulin-dependent (type I) diabetes with severe microvascular disease has failed to substantiate the hypothesis that HLA factors influence the predisposition to this type of complication. A significant association between proliferative retinopathy and raised levels of circulating immune complexes was found. The distribution of insulin-binding levels in serum was similar to that in patients without complications. There was no correlation between insulin binding and the presence of immune complexes and no evidence was found that these complexes contained anti-insulin, anti-nuclear, or organ-specific antibodies. The distribution of insulin-binding levels in these subjects with diabetes of long duration was similar to that observed in 270 subjects with juvenile-onset short-duration type I diabetes. When the data were combined, significant associations between HLA-B8 and low/absent insulin binding levels and B7 with moderate/high insulin-binding levels were observed. HLA-BW62 was not associated with either high or low insulin-binding capacity. It is concluded that HLA genetic factors, insulinbinding capacity, and autoimmunity are unrelated to the pathogenesis of microvascular disease. Raised levels of circulating immune complexes may well be secondary to widespread tissue damage in diabetes of long duration.

Genetic and metabolic studies in diabetic neuropathy

SummaryForty-one diabetic patients with symptomatic diabetic neuropathy were studied together with an equal number of matched diabetic subjects without neuropathy. The acetylator status was determined and HLA-A, B, C and DR antigens were investigated. Metabolic control was assessed by measurement of glycosylated haemoglobin and by the mean of multiple random clinic blood glucose values. No significant difference was observed between the two groups in the proportion of fast and slow acetylators. The distribution of HLA frequencies was similar in subjects with and without neuropathy for both Type 1 (insulin-dependent) and Type 2 (non-insulin-dependent) diabetic patients. When compared with diabetic subjects without neuropathy, the neuropathy group had higher levels of both glycosylated haemoglobin (mean ± SEM: 50.1±1.4 versus 57.5±1.8 mmol hydroxymethylfurfural/mol haemoglobin (10.5±0.3 versus 12.0±0.4% haemoglobin A1, p < 0.01) and mean blood glucose (9.3±0.4 versus 11.3±0.5 mmol/l, p < 0.005). This study provides no evidence that genetic factors increase the susceptibility of diabetic patients to develop neuropathy. In contrast, the elevated glycosylated haemoglobin and blood glucose levels strengthen the association between hyperglycaemia and diabetic neuropathy.

Increased killer cell activity in insulin dependent (Type 1) diabetes mellitus

SummaryAntibody dependent cell mediated cytotoxicity in relation to the levels of circulating killer cells was investigated in 16 newly diagnosed classical insulin dependent (Type 1) diabetics, 11 islet cell antibody positive non diabetic children with at least one HLA haplotype in common with their diabetic sibling, and in 15 normal controls. Antibody dependent cell mediated cytotoxicity was evaluated using, as target, 51Cr labelled human 0+ erythrocytes sensitised with an anti-CD antiserum. Killer cells were measured by the low affinity E-rosetting cell technique. Increased killer cell levels (>normal mean + 2SD) were accompanied by a significant enhancement in antibody dependent cell mediated cytotoxicity both in newly diagnosed diabetics (p < 0.05) and in unaffected siblings (p < 0.01). These preliminary results indicate that raised antibody dependent cell mediated cytotoxicity is a feature of insulin dependent diabetes at diagnosis and suggest that active B cell damage might be occurring some time before the onset of clinical symptoms.

Antibody-dependent and natural killer cytotoxicity in type 1 diabetes

SummaryThe antibody-dependent cell-mediated cytotoxicity and the spontaneous cell-mediated cytotoxicity against Chang liver cells in relation to the levels of circulating K-cells (low affinity E-rosetting cells) were investigated in 23 newly diagnosed insulin-dependent (Type 1) diabetics, and in 17 unaffected islet cell antibody-positive subjects. Antibody-dependent cell-mediated cytotoxicity was significantly increased in those newly diagnosed diabetics with K-cell levels greater than 2 SD above the mean of normal controls (p<0.02). A similar but not significant trend was also found in islet cell antibody-positive subjects with raised K-cells. Spontaneous cell-mediated cytotoxicity was not different in any of the groups. These results lend further support to the concept that antibody-dependent lymphocyte cytotoxicity is enhanced in Type 1 diabetes at diagnosis.