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Different types of diabetes

What is Type 1 diabetes?

Type 1 diabetes is an autoimmune disease that occurs when T cells attack and destroy most of the beta cells in the pancreas that are needed to produce insulin, so that the pancreas makes too little insulin or no insulin. Without the capacity to make adequate amounts of insulin, the body is not able to metabolise blood glucose, to use it efficiently for energy, and ketones can be produced. The onset of Type 1 diabetes may be triggered by environmental factors such as a viral or other infection.

What is Type 2 diabetes?

Type 2 diabetes usually appears in middle-aged or older people, although more frequently it is being diagnosed in younger overweight people, and it is known to affect people from high prevalence ethnic backgrounds at a younger age. Type 2 diabetes occurs when the body is not making enough insulin, or the body is not able to respond to the insulin properly. The risk of developing Type 2 diabetes can be reduced by changes in lifestyle.

What is monogenic diabetes?

Monogenic diabetes is diabetes caused by a change in a single gene. This can broadly be separated into neonatal diabetes and maturity onset diabetes of the young.

  • Neonatal diabetes is diagnosed at less than six months of age and mutations in at least 22 genes are known to cause neonatal diabetes. As mentioned previously all patients with diabetes diagnosed at less than six months of age (whatever their age now) should be referred for genetic testing as they are highly likely to have a monogenic cause of their diabetes.
  • Maturity onset diabetes of the young (MODY) is characterised by three key features:
    • a young age of onset (at least one family member diagnosed below the age of 25 years)
    • autosomal dominant inheritance (diabetes passed down from an affected parent to their child, with diabetes in 2 or more generations
    • non insulin dependent diabetes (or evidence of endogenous insulin production more than 3 years post diagnosis).

There are a number of genes now identified in which mutations cause MODY. The different types of MODY cause different phenotypes. The commonest MODY genes and their key characteristics are briefly summarised below:

  • GCK (Glucokinase) MODY: Mild hyperglycaemia, fasting blood glucose 5.5-8mmol/l, HbA1c 40-60mmol/mol or 5.8-7.6%), often detected during routine screening, no treatment needed, reduced risk of complications.
  • HNF1A MODY: Diabetes often develops during adolescence, sensitive to low dose sulphonylureas, have a low renal threshold for glucose, at risk of diabetic complications, early myocardial infarction.
  • HNF4A MODY: Macrosomia and neonatal hypoglycaemia may be present, sensitive to low dose sulphonylureas.
  • HNF1B MODY: Diabetes and renal cysts, low faecal elastase, low magnesium, usually require insulin treatment, may have uterine abnormalities or gout.

There are other rare causes of monogenic diabetes including Mitochondrially Inherited Diabetes and Deafness (MIDD), Familial Partial Lipodystrophy (FPLD) and you can find out more about these on our Diabetes Genes website.

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This article is from the free online course:

Genomic Medicine: Transforming Patient Care in Diabetes

University of Exeter

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