Maturity onset diabetes of the young (MODY)
Q: What is MODY?
Maturity Onset Diabetes of the Young (MODY) affects one to two per cent of people with diabetes and can often go unrecognised. Its three main features are:
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Diabetes often develops before the age of 25 years
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Diabetes runs in families – being passed on from an affected individual in one generation to someone in the next
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Diabetes is usually treated with lifestyle changes such as a healthier diet and increased physical activity, although some forms of MODY may require treatment with tablets or insulin
Q: Why does MODY run in families?
MODY is due to a change in a single gene that is passed from a parent carrying the affected gene to their child. All children of an affected parent have a 50% chance of inheriting the affected gene and developing MODY themselves.
Q: Why is it important to recognise MODY?
- Currently six types of MODY have been identified. By knowing which type of MODY a person has, the most appropriate treatment can be offered.
- Knowing the type of MODY enables advice to be given about the progression of the diabetes.
Because it is inherited, other family members with diabetes can have genetic testing to confirm the cause of their diabetes, and unaffected family members can have genetic counselling to discuss whether they would like a predictive genetic test in order to determine whether or not they have inherited the affected gene.
Q: How is someone diagnosed with MODY?
MODY is confirmed by a ‘diagnostic genetic test’ that can be arranged by your GP or diabetes consultant. A blood sample is taken locally and then sent to the molecular genetics laboratory at the Royal Devon and Exeter Hospital for analysis. The blood sample needs to be accompanied with a genetic testing form that is completed by the doctor who refers you for the test.
Q: What types (classifications) of MODY are known?
- HNF1 – alpha. This is the gene found to be responsible for 70% of cases of MODY. It causes diabetes by lowering the amount of insulin produced by the pancreas. In childhood sufficient insulin is produced, but the amount of insulin reduces as the person gets older. The diabetes often develops in adolescence or early twenties, but may not be diagnosed until later in life. Good control of blood glucose and cholesterol levels are important in this type of MODY as the small blood vessels can be damaged, causing damage to eyes and kidneys. The large blood vessels may also become damaged, resulting in coronary heart disease. Those with HNF1alpha MODY are particularly sensitive to a group of tablets called sulphonylureas. They can often be well controlled on very small doses of these tablets for many years, although may well progress to needing insulin treatment eventually. Otherwise management recommendations are the same as for others with diabetes - keeping physically active and maintaining a healthy body weight helps to maintain good blood glucose and cholesterol levels.
- Glucokinase. This gene helps the body to recognise how high the blood glucose level is in the body. When this gene is not working properly the body allows the level of blood glucose to be higher than it should be. Blood glucose values in people with glucokinase MODY typically remain between 5.5-8mmol/l. This type of MODY rarely presents with symptoms and no treatment is required. It is often picked up with routine testing and it is important to identify it when a person is pregnant, although complications associated with glucokinase are rare.
- HNF4 – alpha. HNF4A is less common than other forms of MODY. Those who have inherited a change in this gene are likely to have had a birthweight of 9lb or more (around 4 kg). They may also have had a low blood sugar at, or soon after, birth and may have required treatment for this. The diabetes often develops later in life than in other forms of MODY but good control of blood glucose levels remains important. Sulphonylureas are an appropriate treatment for those with HNF4-alpha MODY but, as with HNF1 – alpha, progression to insulin is likely over time. Other management recommendations are the same as for others with diabetes- keeping physically active and maintaining a healthy body weight helps to maintain good blood glucose and cholesterol levels.
- HNF1 – beta. This type of MODY is associated with renal cysts (cysts of the kidneys) and diabetes, and sometimes uterine abnormalities or gout as well. Often the renal cysts can be detected in the foetus in utero. The diabetes tends to develop later and insulin treatment is usually required.
- PDX1 or IPF1. These are the same type of MODY. It it has only been described in one family to date in the UK so little information is available.
- NeuroD1. This type of MODY has only been described in two families so, again, little is known about it.
Q: Will MODY cause complications similar to other types of diabetes?
Originally it was thought that MODY very rarely caused complications, especially microvascular ones (problems with your kidneys, eyes and feet). However, it has now been found that most types of MODY can still lead to complications and therefore keeping strict glycaemic control and keeping your blood pressure and cholesterol well controlled is just as important as with other types of diabetes.
Q: Where can I go for further information and support?
You can find more detailed information about MODY on the Diabetes Genes website, run by the Diabetes Research department and Centre for Molecular Genetics at the Peninsula Medical School, and the Royal Devon and Exeter NHS Foundation Trust. The website address is www.diabetesgenes.org. You can also ask to be put in touch with your local genetic diabetes nurse, details of whom can be found on this website.
In addition you are welcome to call our Careline on 0845 120 2960, Monday to Friday, 9am to 5pm, or email careline@diabetes.org.uk, for more general information about diabetes, and for support.