The genetics and pathophysiology of type II and gestational diabetes

Do intrauterine or genetic influences explain the foetal origins of chronic disease? A novel experimental method for disentangling effects

BACKGROUND

There is much evidence to suggest that risk for common clinical disorders begins in foetal life. Exposure to environmental risk factors however is often not random. Many commonly used indices of prenatal adversity (e.g. maternal gestational stress, gestational diabetes, smoking in pregnancy) are influenced by maternal genes and genetically influenced maternal behaviour. As mother provides the baby with both genes and prenatal environment, associations between prenatal risk factors and offspring disease maybe attributable to true prenatal risk effects or to the "confounding" effects of genetic liability that are shared by mother and offspring. Cross-fostering designs, including those that involve embryo transfer have proved useful in animal studies. However disentangling these effects in humans poses significant problems for traditional genetic epidemiological research designs.

METHODS

We present a novel research strategy aimed at disentangling maternally provided pre-natal environmental and inherited genetic effects. Families of children aged 5 to 9 years born by assisted reproductive technologies, specifically homologous IVF, sperm donation, egg donation, embryo donation and gestational surrogacy were contacted through fertility clinics and mailed a package of questionnaires on health and mental health related risk factors and outcomes. Further data were obtained from antenatal records.

RESULTS

To date 741 families from 18 fertility clinics have participated. The degree of association between maternally provided prenatal risk factor and child outcome in the group of families where the woman undergoing pregnancy and offspring are genetically related (homologous IVF, sperm donation) is compared to association in the group where offspring are genetically unrelated to the woman who undergoes the pregnancy (egg donation, embryo donation, surrogacy). These comparisons can be then examined to infer the extent to which prenatal effects are genetically and environmentally mediated.

CONCLUSION

A study based on children born by IVF treatment and who differ in genetic relatedness to the woman undergoing the pregnancy is feasible. The present report outlines a novel experimental method that permits disaggregation of maternally provided inherited genetic and post-implantation prenatal effects.

A population-based screening for gestational diabetes mellitus in non-diabetic women in Bahrain

BACKGROUND

Maternal hyperglycemia is considered a risk factor for fetal morbidity. Since there is a high prevalence of diabetes mellitus among the population of Bahrain, we conducted a prospective population-based study of gestational diabetes mellitus (GDM) in non-diabetic pregnant women.

SUBJECTS AND METHODS

All non-diabetic pregnant women attending antenatal clinics during January 2001 to December 2002 (n=10,495) were screened for GDM during the 24th to 28th weeks of gestation. All positive subjects based on a 50-g glucose challenge test (GCT) were further evaluated by a diagnostic 75-g oral glucose tolerance test (OGTT). The birth weight of the child and post-delivery insulin resistance were monitored. The homeostasis model of insulin resistance (HOMA-IR) was used to assess insulin resistance.

RESULTS

Of 10,495 non-diabetic pregnant women screened, 32.8% (n=3443) had plasma glucose > or = 7.8 mmol/L (140 mg/dL) in the GCT. The 75-g OGTT found a prevalence of GDM of 13.5%. There were twice as many Bahrainis as expatriates. Of children born to women with GDM, 6.5% had a birth weight > 4000 g. Post-delivery evaluation of insulin resistance indicated that 33% of women with GDM had a HOMA-IR value > 2.

CONCLUSION

The population of Bahrain is a high-risk ethnic group for GDM. The association of insulin resistance in the post-gravid state with GDM among 33% of the study population suggests that insulin resistance, the possible cause of the pathophysiological mechanism underlying the development of gestational diabetes, continues in the post gravid state.

Improving the care of women with gestational diabetes

The article reviews gestational diabetes mellitus, including etiology, diagnostic and screening criteria, risk factors, and care of the affected woman. Gestational diabetes mellitus affects approximately 7% of all pregnant women, resulting in more than 200,000 cases each year, and is defined as glucose intolerance that begins or is first recognized during pregnancy. Women are considered at high risk for gestational diabetes if they are markedly obese, have a personal history of gestational diabetes, have a strong family history of diabetes, or have glycosuria. Risk assessment is essential in determining whether a woman should be screened or tested for gestational diabetes. Women who have had gestational diabetes should have comprehensive preconception care prior to a subsequent pregnancy to ascertain appropriate weight, nutrition, exercise, and signs of gestational diabetes.

Metabolic and steroidogenic alterations related to increased frequency of polycystic ovaries in women with a history of gestational diabetes

The prevalence of polycystic ovaries (PCO) and clinical, endocrine, and metabolic features were investigated in women with previous gestational diabetes (GDM). Thirty-three women with a history of GDM and 48 controls were studied. Glucose and insulin secretion capacity was evaluated by means of the oral glucose tolerance test (OGTT), and insulin action was determined by means of a euglycemic insulin clamp. Compared with control women, women with previous GDM more often had significantly abnormal OGTT, a higher prevalence of PCO (39.4% vs. 16.7%; P = 0.03), higher serum concentrations of cortisol, dehydroepiandrosterone, and dehydroepiandrosterone sulfate and a greater area under the glucose curve. Women with previous GDM showed a lowered early phase insulin response to glucose and impaired insulin sensitivity, which was accounted for mainly by decreased glucose nonoxidation. They also demonstrated a significantly lower fasting serum C peptide/insulin ratio than the controls, indicating that women with previous GDM have impaired hepatic insulin extraction, which tended to be more marked among women with PCO. This may explain why women with PCO and previous GDM were significantly more hyperinsulinemic than women with normal ovaries. In conclusion, our data demonstrate that women with previous GDM often have PCO and abnormal OGTT. They are insulin resistant as a result of lowered glucose nonoxidation and show inappropriately low insulin responses to glucose, reflecting impaired beta-cell function. They also have higher adrenal androgen secretion, which may be associated with abdominal obesity.

The genetic basis of diabetes mellitus

Familial risk, pathogenesis, clinical onset, and treatment of diabetes mellitus vary according to etiology. Although Type 2 diabetes has a higher familial risk, more is known about the genetics of Type 1 diabetes. Genes contributing 60% to 65% of susceptibility to Type 1 diabetes mellitus are known. Type 1 diabetes is associated with susceptibility genes in the HLA region on chromosome 6p21 and the insulin gene on chromosome 11p15, and at least eight additional susceptibility genes are under investigation. Islet cytoplasmic antibodies provide humoral evidence of Type 1 diabetes risk. Only 10% of the genes contributing susceptibility to Type 2 diabetes mellitus are known, and they are primarily associated with uncommon subtypes of the disorder. The insulin receptor gene on chromosome 19p13 and at least five glucose transporter genes contribute to Type 2 diabetes susceptibility, and further associations may emerge from study of the glycogen synthase gene, the glucokinase gene, the MODY genes, and the leptin gene. Diabetes comorbidities may result from genetic and environmental susceptibilities independently or in combination.