Heterogeneity of insulin secretion in type II diabetes

Maturity onset diabetes of the young (MODY)--history, first case reports and recent advances

The world is seemingly facing a global increase in people suffering from diabetes especially in developing countries. The worldwide occurrence of diabetes for all age groups in year 2000 was estimated to be 2.8% and this number is most certainly expected to rise to 4.4% by 2030. Maturity-onset of diabetes of the young, or MODY, is a form of monogenic diabetes that is caused by mutations occurring in a number of different genes. Mutations in different genes tend to cause a slightly different variant of diabetes. MODY is typically diagnosed during late childhood, adolescence, or early adulthood and is usually observed to develop in adults during their late 50's. One of the main drawbacks in its diagnosis is that many people with MODY are misdiagnosed as having type 1 or type 2 diabetes. However, a molecular and genetic diagnosis can result in a better treatment and could also help in identifying other family members with MODY. This article explores the historical prospect and the genetic background of MODY, a brief summary of the first case reported and the significant factors that differentiate it from type 1 and type 2 diabetes.

Glucokinase as pancreatic beta cell glucose sensor and diabetes gene

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Insulin therapy in maturity-onset diabetes

A prime target of insulin action in patients with maturity onset diabetes is suppression of hepatic glucose production in both the fasting and postprandial states. In patients who fail to respond to oral treatment insulin improves glycaemic control, has an antiatherogenic effect on the serum lipoprotein pattern, and increases well being. The beneficial long-term effects of insulin therapy on morbidity and mortality are, however, still unproved. The regimens of insulin therapy are not established. In patients with normal or increased basal serum C-peptide concentration treatment may start with intermediate or long-acting insulin at bedtime together with oral medication, or in the morning with or without oral medication. If this fails two injections of intermediate-acting insulin or multiple injections of short-acting insulin should be started. Hypoglycaemia is uncommon in maturity onset diabetes treated with insulin, but moderate weight gain usually occurs. The possible role of hyperinsulinemia as a predisposing factor for atherogenesis remains unresolved. Despite controversies over treatment, any patient with maturity onset diabetes not responding to oral agents should be regarded as a candidate for insulin therapy.

Sequential changes in serum insulin concentration during development of non-insulin-dependent diabetes

Changes in serum insulin concentrations during deterioration of glucose tolerance were studied in 81 Pima Indians who worsened from normal to impaired glucose tolerance (IGT); 44 who changed from IGT to non-insulin-dependent diabetes mellitus (NIDDM); 27 who were seen at diagnosis of NIDDM and 1.4-8.5 years later; and 11 subjects who were seen at each of these stages. When their glucose tolerance was normal, subjects who later developed NIDDM had higher fasting and post-load insulin concentrations than controls of similar age and body mass index who did not become diabetic. Onset of IGT or NIDDM was associated with a further increase in fasting insulin concentrations, although a deterioration from IGT to NIDDM was associated with little change in insulin responses to oral glucose in spite of increased blood glucose. After the onset of NIDDM, both fasting and post-load insulin concentrations diminished. These longitudinal data show that, as glucose tolerance worsens, insulin and glucose concentrations in individuals follow the inverted-U-shaped relation previously reported in cross-sectional population studies.

Pathogenesis of NIDDM--a disease of deficient insulin secretion

Type 2 diabetes is a familial disease and studies of both Caucasian and Japanese families have raised the possibility that a major susceptibility gene is involved. The majority of patients have both beta cell dysfunction and impaired insulin sensitivity but studies of relatives of Type 2 diabetic patients suggest that beta cell dysfunction is an early feature of the disease. Impaired insulin sensitivity, from acromegaly, Cushing's disease or steroid therapy, induces diabetes only in a small proportion of the population, and they may be those who have an inherited cell defect. We postulate that a single beta cell defect gene, on its own, may be insufficient to cause overt diabetes and would lead to life-long glucose intolerance unless associated with other defects such as impaired insulin sensitivity. The nature of such a postulated beta cell defect is uncertain. Whilst it has been reported to be specific to glucose, and not to non-glucose stimuli, this feature may be secondary to hyperglycaemia. The occurrence of islet amyloid in 70-90% of Type 2 diabetic patients, and rarely in the normal population, raises the possibility that amyloid deposition causing disruption of the islet is a factor which might affect beta cell function. Amyloid formation may be a primary abnormality or could be secondary to beta cell dysfunction induced by hyperglycaemia. A major susceptibility gene might predispose a proportion, perhaps 10-15%, of a Caucasian population towards diabetes. The subsequent development of diabetes in a particular patient is likely to depend on many factors including other genetic factors, a sedentary life style and obesity. In different populations different genetic influences may operate, including abnormalities of insulin receptor genes and glucose transporter genes, which may allow a beta cell abnormality to become expressed clinically.

Linkage analysis of the human insulin receptor gene and maturity onset diabetes of the young

The cloning of the insulin receptor cDNA has permitted the definition of restriction fragment length polymorphisms at that locus. These polymorphisms were used to study the role of the insulin receptor in four pedigrees with maturity onset diabetes of the young through linkage analyses. When each pedigree was individually analysed, no linkage was demonstrated in the two larger pedigrees, implying that an insulin receptor defect was not responsible for the predisposition to diabetes in these pedigrees. One of these pedigrees was known to be hypoinsulinaemic, while insulin levels were unavailable in the second pedigree. In the two smaller pedigrees, however, a single haplotype cosegregated with diabetes. One of these pedigrees is known to be hyperinsulinaemic. The small size of the pedigrees which demonstrated cosegregation precluded statistical proof of linkage. Nonetheless, the presence of an uncommon insertional polymorphism which cosegregated with diabetes in both pedigrees was improbable and suggested that this insertion could be responsible for diabetes in these families. This study thus may be additional evidence for heterogeneity in maturity onset diabetes of the young. For the two larger pedigrees, the insulin gene and HLA region have already been eliminated as genetic markers. This study provides data which eliminate a third candidate gene in these two pedigrees.