Genetics of non-insulin dependent diabetes mellitus in 1990

The prevention of type 2 diabetes--lifestyle change or pharmacotherapy? A challenge for the 21st century

Diabetes mellitus is occurring in epidemic proportions in many countries. In Australia 7.4% of people over 25 years of age have diabetes (mostly type 2) and comparable or higher prevalences have been reported in the United States and a number of Asian countries. The enormous economic and social cost of this disease makes a compelling case for prevention. Epidemiological studies have shown clearly that type 2 diabetes results from an interaction between a genetic predisposition and lifestyle factors including obesity, sedentary behaviour and both calorie excess and various dietary constituents. The natural history of type 2 diabetes includes a preceding period of impaired glucose tolerance (IGT)/impaired fasting glucose (IFG) which provides an opportunity for targeted intervention within large communities. Lifestyle intervention studies have consistently shown that quite modest changes can reduce the progression from IGT to diabetes by 50-60%. It may, however, not be possible to translate these successful findings to larger cohorts or maintain the lifestyle changes longer term. This has lead to consideration of pharmacotherapy. While small studies with sulphonylureas are inconclusive, benefits have been found for metformin, acarbose and troglitazone. Big intervention studies with ramipril, rosiglitazone, valsartan and nateglinide are underway. Pharmacological intervention raises a whole range of ethical, economic and practical issues not the least of which is the problem of long term therapy of the 'otherwise well'.

Importance of family history in type 2 black South African diabetic patients

OBJECTIVE

To assess the family history of diabetes in type 2 black South African diabetics with emphasis on the parental phenotype.

DESIGN

Prospective case-control study in which family histories were obtained from patients.

SETTING

Diabetic clinic of a provincial teaching hospital in the Transkei region of South Africa.

SUBJECTS

A total of 1111 type 2 diabetics attending the diabetic clinic and 687 controls.

MAIN OUTCOME MEASURES

History of diabetes in parents, siblings, maternal and paternal grandparents, aunts, and uncles.

RESULTS

Altogether 27.3% of diabetic subjects had a family history of diabetes compared with 8.4% in the control group (p<0.01). Among the group with positive family history 82.6% reported only one diabetic family member, while 17.4% reported at least two relatives; 6.6% had a diabetic relative from both maternal and paternal sides, and 87.8% had first degree relative with diabetes. Among them there was a significant maternal aggregation with 64.7% of patients having a diabetic mother compared with 27% who had a diabetic father (p<0.01). No maternal effect was observed among the second and third degree relatives. Patients with positive family history had an earlier onset of diabetes than those without family history (p<0.01).

CONCLUSION

These data suggest that type 2 diabetes is heritable in black South African diabetics. It is also likely that maternal influences may play an important part.

Prevention of type 2 diabetes

Type 2 diabetes is a major cause of morbidity and mortality resulting from its microangiopathic and macroangiopathic complications. Current approaches to its management and to the prevention of diabetic complications are difficult to implement effectively, and there is little evidence to date that these approaches are reducing the impact of this disease. The recognition that type 2 diabetes usually has a prolonged prediabetic phase raises the possibility that the emergence of hyperglycemia and the atherosclerotic complications associated with diabetes may be preventable by the institution of early treatment modalities. Sufficient data suggest that life-style modification or pharmacotherapy directed at improving insulin sensitivity or insulin secretion in subjects with impaired glucose tolerance may reduce progression to diabetes. Two long-term prospective, controlled trials have been initiated to test this hypothesis.

Health risks of immigration: the Yemenite and Ethiopian cases in Israel

Immigration almost always involves major cultural changes in dietary, social and health-related beliefs and behaviour. Two years after the arrival of the earliest Yemenite immigration wave to Israel, about 30 years ago, the prevalence rate of diabetes in that population was almost nonexistent (approximately 0.06%), increasing to approximately 12% 25 years later. Obesity and hyperlipoproteinemia were not always correlated with diabetes. Ethiopians, mainly from the northern regions, first immigrated to Israel ten years ago. At that time, their prevalence rate of diabetes was 0-0.4%. Though it is too early to determine the overall prevalence rate in this population, 5-8% rates have been reported after up to 5 years in Israel. The objective of the present work was to study the effect of the diversity of ethnic food patterns and adaptability on the nutritional status of Ethiopian immigrants. Two groups were studied--teenagers and adults. After 2 and 18 months in Israel, adult Ethiopians who arrived in Israel in 1991 (n = 426) had an average body mass index (BMI) of 20-22 kg/m2, which was below western values; a waist:hip ratio (WHR) of 0.9 suggested abdominal fat accumulation. Fasting serum- glucose levels were within the norm, whereas insulin levels were high (24 micrograms/mL). Plasma triglycerides (TG) increased with age, from about 100 to 150 mg/dL, whereas cholesterol and lipoprotein levels remained stable and normal. The BMI of Ethiopian teenagers (n = 15) 5-7 years in Israel was similar to that found in adults. Fasting serum insulin levels were significantly lower in boys than in girls (approximately 16.6 vs approximately 18.6 microU/mL, respectively). Cholesterol values were significantly higher in girls than in boys (approximately 184 vs approximately 150 mg/dL); TG, high density and low density lipoprotein values were normal. These data indicate the existence of early signs of risk factors for diabetes, which may not manifest itself clinically unless provoked. Several causes, rendered detrimental by progress, could be setting the stage for early manifestation of risk factors for cardiovascular disease and diabetes. Of these, two are of pertinence to this work: a genetic endowment for low-energy output and the thrifty genotype, and maternal undernutrition.

Pathogenesis of feline diabetes mellitus

Cats are one of the few species that develop a form of diabetes mellitus that is clinically and histologically analogous to human type 2 diabetes mellitus. Figure 9 summarizes the etiologic factors thought to be involved in the development of feline and human type 2 diabetes. The main metabolic characteristics of type 2 diabetes mellitus are impaired insulin secretion and resistance to the action of insulin in its target tissues. Impaired beta cell function occurs before histologic changes become evident. The characteristic histologic finding in cats with type 2 diabetes is deposition of amyloid in pancreatic islets. Amyloid deposition occurs before the onset of clinical signs, but does not seem to be the primary defect. Pancreatic amyloid is derived form the recently discovered pancreatic hormone amylin. Amylin is synthesized in pancreatic beta cells, and is co-stored and co-secreted with insulin. Amylin has been postulated to be involved in the pathogenesis of feline diabetes mellitus both through its metabolic effects, which include inhibition of insulin secretion and induction of insulin resistance, and via progressive amyloid deposition and beta cell degeneration. Increased amylin concentration has been documented intracellularly in cats with impaired glucose tolerance and in the plasma of diabetic cats, and supports the hypothesis that amylin is involved in the pathogenesis of type 2 diabetes. Obesity is a common finding in diabetic felines and is a contributing factor to the insulin resistance present in type 2 diabetes. Clinical signs of diabetes develop once total insulin secretion decreases to 20% to 25% of normal levels. Many diabetic cats have been treated successfully with oral hypoglycemics, but 50% to 70% of diabetic cats are insulin dependent. Based on histologic evidence, this is the result of extensive amyloid deposition and subsequent beta cell degeneration, rather than autoimmune destruction of pancreatic beta cells associated with type 1 diabetes. Alternative ways of treating type 2 diabetes currently are being investigated. Amylin antagonists recently have been proposed as a novel treatment to reverse the deleterious effects of excessive amylin concentrations. The gastrointestinal hormone glucagon-like peptide-1 may also prove useful in treating diabetic cats, because of its stimulatory effect on insulin secretion and synthesis, and the absence of significant hypoglycemic effect.

Family studies of non-insulin-dependent diabetes mellitus in South Indians

Though a genetic basis for non-insulin-dependent diabetes mellitus (NIDDM) is clear, the likely mode of inheritance is not known. The segregation of NIDDM was studied in 64 nuclear South Indian pedigrees (449 individuals) ascertained through an affected proband having both parents and more than 1 sibling alive and available for oral glucose tolerance testing. A high proportion of parents were found to be of abnormal glucose tolerance [89 of 128 (70%) diabetic and 11 of 128 (9%) impaired]. Complex segregation analysis was performed using (1) POINTER which implements the mixed model and distinguishes major gene, multifactorial and non-transmitted environmental contributions to affection and (2) COMDS which implements an oligogenic model with major gene, modifier gene and environmental contributions to a) affection and b) diathesis (an ordered polychotomy amongst non-affected family members, based on 2-h plasma glucose level). Using POINTER, there was no formal support for a major gene and the most parsimonious solutions were achieved with multifactorial models. Using COMDS, we found i) significant improvements in models when information on glucose levels in nondiabetic family members (diathesis) was included, ii) support for segregation of a diallelic gene as well as background familial resemblance, and iii) under the best-supported model, this diallelic locus featured incomplete dominance (d = 0.8) and a disease-predisposing allele frequency of 14%. In South Indians, segregation of NIDDM is inadequately described by simple major gene models: more complex models provide more satisfactory descriptions. This finding, if applicable in other populations, has important implications for the search for diabetes-susceptibility genes.

A review of new developments in type 2 diabetes in human beings and cats

Cats appear to be one of the few non-human species that develop a type of diabetes mellitus analogous to human Type 2, or non-insulin-dependent diabetes mellitus (NIDDM). In this review, some current theories on diabetogenesis are discussed. In both cats and human beings, Type 2 diabetes is characterized by impaired insulin secretion due to a functional defect in pancreatic beta-cells, and insulin resistance. In both species, amyloid deposition occurs in pancreatic islets and is derived from the newly discovered pancreatic hormone islet amyloid polypeptide (IAPP), or amylin. Amylin also reduces insulin secretion and induces insulin resistance. Thus, the hypothesis of amylin being intimately involved in the pathogenesis of human and feline Type 2 diabetes appears justified. Obesity is a frequent concomitant problem in feline and human Type 2 diabetes and contributes to the insulin resistance characteristic of the disease.

Positive association in the absence of linkage suggests a minor role for the glucokinase gene in the pathogenesis of type 2 (non-insulin-dependent) diabetes mellitus amongst south Indians

Mutations of the glucokinase gene have been implicated in the development of glucose intolerance in pedigrees with maturity-onset diabetes of the young. However, the contribution of the glucokinase gene to the aetiology of common Type 2 (non-insulin-dependent) diabetes mellitus is uncertain. We have studied the role of the glucokinase gene in the pathogenesis of Type 2 diabetes in South Indians, using both population-association and linkage methodology. A pair of CA-repeat sequences (GCK(3') and GCK(5')) straddling the glucokinase gene were employed as markers, each subject being typed using the polymerase chain reaction and polyacrylamide gel electrophoresis. Comparisons of allele frequencies at these markers were made between 168 Type 2 diabetic subjects and 70 racially-matched control subjects. No differences in allele frequencies were apparent at the GCK(5') marker; however, there were significant differences in allele frequencies at the GCK(3') marker between the Type 2 diabetic subjects and control subjects (chi 2 = 11.6, df = 3, p = 0.009) with an increase of the z allele (78.0% vs 66.4%) and a decrease of the z + 2 allele (13.7% vs 25.0%) amongst the diabetic subjects. Linkage between glucose intolerance and the glucokinase gene was studied in 53 nuclear pedigrees under a variety of genetic models. Linkage was excluded (lod score < -2) at a recombination fraction of zero under five of the ten models used and highly unlikely (-2 < lod score < -1) under the others. The combination of positive association and negative linkage suggests that glucokinase acts as a minor gene influencing the development of Type 2 diabetes within this population.

The etiology and pathogenesis of non-insulin-dependent diabetes

Although environmental factors are important triggers of non-insulin-dependent diabetes mellitus (NIDDM), heredity plays a major role in the pathogenesis of the disease. Insulin resistance manifested as impaired activation of glycogen synthase and thereby storage of glucose as glycogen in skeletal muscle is demonstrable early on in NIDDM relatives, suggesting that NIDDM could be an inherited muscle disease. On the other hand, insulin deficiency is almost unequivocally present before manifest diabetes develops. An intensive search for candidate genes for NIDDM has been initiated; so far it has not been possible to ascribe NIDDM to any alterations in the human genome. Given the heterogenous nature of NIDDM, its age-dependent penetrance and strong influence of environmental factors, it may not be fruitful to use NIDDM as an end-point in genetic linkage or association studies. It is more likely that DNA defects result in either insulin resistance or insulin deficiency, which in turn, can both lead to NIDDM. In accordance with the thrifty gene hypothesis, the insulin resistance gene has protected individuals during long periods of starving by storing energy as fat rather than as glycogen in muscle. The abundance of food in Western society has made this once protective gene a deleterious one, suggesting that these individuals are not equipped with the metabolic machinery to handle overeating.