When diabetes doesn't fit the label: LADA, MODY and other types

Why the type of diabetes matters

Type 1 and type 2 diabetes are treated differently, and so are the less common types. A wrong label can mean years of insulin injections that weren't needed, or tablets that were never going to work.

LADA: slow-onset autoimmune diabetes in adults

Latent autoimmune diabetes in adults (LADA) is autoimmune, like type 1, but develops slowly. At diagnosis it looks like type 2: people manage without insulin at first. It accounts for 2 to 12% of adult-onset diabetes.

Clues: diagnosis over 30 but a lean build; other autoimmune conditions such as thyroid disease, in you or your family; tablets that stop working within a few years.

GAD antibodies confirm it. C-peptide, which measures how much insulin your pancreas still makes, guides treatment: an international expert panel recommends insulin, as in type 1, when C-peptide is already low.

MODY: diabetes caused by a single gene

Maturity-onset diabetes of the young (MODY) is caused by a change in one gene and runs in families: each child of an affected parent has a one-in-two chance of inheriting it. In a UK study, 3.6% of people diagnosed with diabetes at 30 or younger had a monogenic cause. Many cases are missed: a UK estimate put the proportion undiagnosed above 80%, and although testing has improved since, the classic textbook criteria still miss many people.

Clues: diagnosis under about 35; a parent and grandparent with diabetes; no antibodies; your own insulin production still measurable three or more years after diagnosis; diabetes found in pregnancy in a slim woman with a raised fasting glucose.

The diagnosis changes treatment. The commonest types respond differently:

• GCK-MODY causes a mild, stable rise in glucose that usually needs no treatment outside pregnancy
• HNF1A and HNF4A-MODY often respond to a particular type of tablet better than to insulin, and some people can stop insulin under supervision

Other causes

Diabetes after pancreatitis or pancreatic surgery, with cystic fibrosis, with iron overload (haemochromatosis), or brought on by steroids.

The tests

• C-peptide, by blood or by a urine test (urinary C-peptide creatinine ratio)
• Islet autoantibodies: GAD, IA-2 and ZnT8. They are most informative close to diagnosis, and can become negative years later
• The Exeter MODY probability calculator, a free online tool that estimates the chance of MODY from your history
• Genetic testing, when the probability justifies it

UK researchers have shown that working through these tests step by step finds monogenic diabetes reliably without testing everyone.

What a new diagnosis can mean

A change of treatment, which should be supervised; testing for relatives; and specific advice for pregnancy.

If you think the label might be wrong

Please don't stop or reduce insulin on your own. Bring what you have to the appointment: when and how you were diagnosed, how soon you needed insulin, any antibody or C-peptide results, and who in your family has diabetes, going back as far as you can. My research at Oxford was in type 1 diabetes and MODY, and working out which type of diabetes someone has is a particular interest of mine.