Maturity onset diabetes of youth

MODY refers to a group of monogenic forms of diabetes with autosomal dominant inheritance. The causative mutations are all in genes that control production of insulin and thus MODY is characterised by relative insulinopaenia but ketosis is an unusual feature of MODY. Diagnosis can be confirmed by molecular genetic analysis. Treatment is by OHA or by insulin therapy depending on the type.

FBC

Baseline haematological and biochemical investigations are mandatory in all newly presenting cases of diabetes.

Urea and electrolytes

Assessment of urea and creatinine is essential to gauge renal function.

Liver function tests

Baseline haematological and biochemical investigations are mandatory in all newly presenting cases of diabetes.

Fasting or random glucose

WHO criteria for diagnosis of diabetes mellitus should be applied.

These are that a fasting plasma glucose >7 mmol/L or a random plasma glucose >11.1 mmol/L on one occasion in symptomatic patients, or two occasions in asymptomatic patients, indicates a diagnosis of diabetes mellitus.

If these criteria are not met it may be necessary to perform a 75g oral glucose tolerance test. The same biochemical cut offs are used for the fasting (7 mmol/L) and two hour (11.1 mmol/L) values.

Fasting lipid profile

A baseline lipid profile is a mandatory investigation in all newly presenting cases of diabetes.

ECG

Not normally necessary but may be performed if there is suspicion of pre-existing ischaemic heart disease.

HbA1c

This is often performed at diagnosis but in actual fact contributes very little at this stage as it will almost invariably be elevated.

While there is a move to have HbA1c adopted as a diagnostic test for diabetes neither the WHO or ADA have yet made this move.

Auto antibodies

Gad antibodies and islet cell antibodies will generally be negative in cases of MODY, helping to differentiate from T1DM where these will usually be positive.

C-peptide levels

C-peptide levels will be normal or low in the fasted state helping to distinguish MODY from T2DM where these will usually be high.

Renal ultrasound scan

There is an association of some types of MODY with cystic renal disease and therefore renal USS should be considered especially if there is any abnormality of renal function.

Molecular genetic testing

If there is sufficient clinical suspicion that the patient may have MODY then they should be offered molecular genetic testing. This enables a confident diagnosis to be made, may affect the treatment they are prescribed and has implications for other family members.

In the UK, the Peninsula Molecular Genetics Laboratory should be contacted and can advise on how to go about arranging the testing.

Patients should be counselled about advantages and disadvantages of genetic testing before a sample is taken and it may therefore be necessary to arrange referral for formal genetic counselling.

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