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Evidence for a genetic basis for type 2 diabetes and the metabolic syndrome has been derived from studies of families, twins and populations with genetic admixture. Identification of genes associated with disease pathogenesis is now underway using techniques such as genome scanning by positional cloning and the candidate gene approach. Genome scanning in several different ethnic groups has identified chromosome regions harbouring type 2 diabetes susceptibility genes such as the novel gene, calpain 10 (CAPN10). The hepatic nuclear factor 4alpha (HNF4alpha) gene partly explains the linkage peak on chromosome 20, while the upstream transcription factor (USF1) is associated with familial combined hyperlipidaemia (FCHL) and maps close to the type 2 diabetes associated 1q peak. Peroxisome proliferator-activated receptor gamma (PPARgamma) was identified as a candidate gene based on its biology. A Pro12Ala variant of this gene has been associated with an increased risk of type 2 diabetes. Many genes accounting for monogenic forms of diabetes have been identified--such as maturity onset diabetes of the young (MODY); glucokinase (GCK) and HNF1alpha mutations being the most common causes of MODY. GCK variants result in 'mild' diabetes or impaired glucose tolerance (IGT) and relatively few cardiovascular complications, while HNF1alpha-associated MODY is more typical of type 2 diabetes, frequently being treated with sulphonylureas or insulin and resulting in microvascular complications. Testing for single gene disorders associated with type 2 diabetes and obesity may determine cause, prognosis and appropriate treatment; however, for the more common polygenic diseases this is not the case. In type 2 diabetes, molecular genetics has the potential to enhance understanding of disease pathogenesis, and help formulate preventative and treatment strategies.

Diabetes mellitus is a chronic metabolic disorder characterized by hyperglycemia and is associated with microvascular and macrovascular complications. Diabetes is the leading cause of noncommunicable diseases worldwide and has reached epidemic proportions in certain parts of the world and in certain ethnic groups. Type 1 diabetes (T1D) is due to autoimmune destruction of insulin-secreting pancreatic β -cells of islets of Langerhans. Type 2 diabetes (T2D) is a multifactorial disease with genetic and environmental factors (especially those causing obesity) playing a key role in its pathogenesis. T2D is the most common form of diabetes worldwide accounting for 90% of cases globally and affecting approximately 4% of the world's adult population. Both T1D and T2D are distinct from ‘other causes of diabetes’ as defined by the etiological classification of the World Health Organization (WHO), which include maturity onset diabetes of the young (MODY) and fibrocalculous pancreatic diabetes (FCPD). Gestational diabetes (GDM) is the fourth category defined by the s WHO.

The results of her basal pituitary function tests taken at that time are tabulated below ( table 1 ). These results suggest adrenocorticotropic hormone (ACTH), thyroid stimulating hormone (TSH) and prolactin deficiencies. A repeat MRI scan of her pituitary demonstrated a normal pituitary gland with no optic chiasmal compression, nor evidence of pituitary haemorrhage. In view of the spontaneous resolution of her visual field defect and pituitary macroadenoma, together with the ACTH and TSH deficiencies, a clinical diagnosis of lymphocytic hypophysitis was made. The patient was treated with hydrocortisone and thyroxine. On further follow-up, she remains well with no headaches or visual disturbances, a normal menstrual cycle and improved energy levels.

Evidence for a genetic basis for type 2 diabetes and the metabolic syndrome has been derived from studies of families, twins and populations with genetic admixture. Identification of genes associated with disease pathogenesis is now underway using techniques such as genome scanning by positional cloning and the candidate gene approach. Genome scanning in several different ethnic groups has identified chromosome regions harbouring type 2 diabetes susceptibility genes such as the novel gene, calpain 10 (CAPN10). The hepatic nuclear factor 4alpha (HNF4alpha) gene partly explains the linkage peak on chromosome 20, while the upstream transcription factor (USF1) is associated with familial combined hyperlipidaemia (FCHL) and maps close to the type 2 diabetes associated 1q peak. Peroxisome proliferator-activated receptor gamma (PPARgamma) was identified as a candidate gene based on its biology. A Pro12Ala variant of this gene has been associated with an increased risk of type 2 diabetes. Many genes accounting for monogenic forms of diabetes have been identified--such as maturity onset diabetes of the young (MODY); glucokinase (GCK) and HNF1alpha mutations being the most common causes of MODY. GCK variants result in 'mild' diabetes or impaired glucose tolerance (IGT) and relatively few cardiovascular complications, while HNF1alpha-associated MODY is more typical of type 2 diabetes, frequently being treated with sulphonylureas or insulin and resulting in microvascular complications. Testing for single gene disorders associated with type 2 diabetes and obesity may determine cause, prognosis and appropriate treatment; however, for the more common polygenic diseases this is not the case. In type 2 diabetes, molecular genetics has the potential to enhance understanding of disease pathogenesis, and help formulate preventative and treatment strategies.