Occasionally, clinicians see patients with diabetes that does not fit the usual pattern of either type 1 or type 2 diabetes and can be considered ‘atypical diabetes’. Subtypes include monogenic, mitochondrial and ketosis-prone diabetes and latent autoimmune diabetes of adults. GPs need a high index of suspicion for these subtypes as treatment and prognosis may vary from those of type 1 and type 2 diabetes.
- Recognition of patients with atypical diabetes is important because of the therapeutic and prognostic implications of this diagnosis.
- Patients with atypical diabetes have often been misdiagnosed with type 1 or type 2 diabetes and in some cases committed to unnecessary insulin therapy and screening for complications.
- Maturity onset diabetes of the young (MODY) is most commonly caused by a mutation in the gene encoding hepatocyte nuclear factor 1-alpha; initial treatment is low-dose sulfonylurea therapy.
- MODY caused by mutations in the gene encoding gluco- kinase does not require treatment outside of pregnancy.
- Type 1 diabetes diagnosed before 6 months of age should prompt screening for neonatal diabetes genes, which may lead to discontinuation of insulin therapy.
- Ketosis-prone diabetes should be considered in patients presenting with ketoacidosis and a type 2 diabetes phenotype.
- Latent autoimmune diabetes in adults can be considered as slowly progressive type 1 diabetes.
- Maternally inherited diabetes and early deafness are clues to the possibility of mitochondrial diabetes.
- Genetic molecular testing is available, and patients with atypical diabetes should be referred for specialist assessment.