Maturity onset diabetes of youth

Polyuria and polydipsia are the cardinal symptoms of diabetes and occur when the blood glucose level exceeds the renal threshold for glucose excretion - usually approximately 10 mmol/L.

However, MODY often presents with relatively mild hyperglycaemia and therefore osmotic and other classical hyperglycaemic symptoms can be absent at presentation.

Variable difficulty with focusing - that has been present for only a short period and is fluctuating - is due to osmotically driven swelling of the lens and varies as the degree of hyperglcaemia varies.

However, MODY often presents with relatively mild hyperglycaemia and therefore osmotic and other classical hyperglycaemic symptoms are often absent at presentation.

Significant weight loss in association with a new diagnosis of diabetes is a less common feature of MODY.

This feature, especially in a patient who is already lean, should prompt the physician to consider a diagnosis of type 1 diabetes or other causes of diabetes, for example post-pancreatitis diabetes.

Hyperglycaemia impairs neutrophil and macrophage function at the same time as producing a more favourable environment for micro-organisms to grow.

Infections generally are therefore more common in the hyperglycaemic patient and genital candidiasis is a particularly prevalent example.

However, MODY often presents with relatively mild hyperglycaemia and therefore osmotic and other classical hyperglycaemic symptoms are often absent at presentation.

A thorough family history is essential to detect monogenic causes of diabetes such as MODY.

In addition, mitochondrial diabetes or APECED (auto-immune polyendocrinopathy, candidiasis and ectodermal dystrophy) might also be missed without a good family history being taken.

Because MODY is usually inherited as an autosomal dominant trait, the family history with members of each successive generation being affected ought to be fairly obvious.

To confidently diagnose MODY, there needs to be a strong family history of diabetes mellitus with onset before the age of 25. T2DM also however often runs quite strongly in families.

A complete absence of family history of diabetes doesn’t absolutely rule out the diagnosis of MODY but should at least prompt consideration of alternative diagnoses which may include T1DM or LADA. 

This would increase the chances of steroid induced diabetes and reduce the probability of MODY.

Any of these conditions may pre-dispose to loss of beta cell mass. If so, this would indicate a cause of diabetes other than MODY.

As awareness of MODY increases there are an increasing number of first degree relatives of index cases being screened at a pre-symptomatic stage and found to have early, pre-symptomatic diabetes.

However, the history of family screening for a 'genetic' form of diabetes ought to be quite apparent. Because some forms of MODY present with relatively mild hyperglycaemia, diagnosis can also be made in an asymptomatic patient after the chance finding of an elevated blood glucose level.

Are there family members with diabetes who have spent many years successfully managing with diet-only therapy and who have acquired very few, if any, diabetes complications? 

Are there family members with diabetes mellitus who have only required very low doses of sulphonylurea drugs, such as gliclazide or glibenclamide, for prolonged periods of time giving good control of their diabetes? 

Are there family members who have been diagnosed with T1DM but who have required very low doses of insulin to achieve good control of their diabetes, or who have later come off insulin therapy and required only tablet treatment, or who have had prolonged 'honeymoon' phases of their diabetes?