When should diabetes be investigated for a rare or genetic form?

Diabetes is classified according to its underlying cause, and determining the correct type requires more than looking at a person’s age, weight or blood glucose levels.

While type 1 and type 2 diabetes are the most common forms, an atypical clinical picture may indicate a different form of diabetes that requires more specialised investigation.

How is diabetes classified?

Diabetes is broadly classified according to the mechanism responsible for persistent high blood glucose. The main categories are type 1 diabetes, type 2 diabetes, gestational diabetes and other specific forms, including diabetes caused by genetic conditions, pancreatic disease, endocrine disorders or certain medicines.

Type 1 diabetes occurs when the immune system destroys the insulin-producing beta cells in the pancreas, resulting in an absolute lack of insulin.
Type 2 diabetes develops through a combination of insulin resistance and progressive impairment of insulin secretion.
Gestational diabetes is diabetes first diagnosed during pregnancy, while other specific forms have an identifiable underlying cause.

What determines whether someone has type 1, type 2 or another form of diabetes?

The type of diabetes is determined by the overall clinical picture. No single characteristic, such as age or body weight, is sufficient to establish the diagnosis.

Several features can suggest that the initial classification may need to be reconsidered:

Diabetes developing at an unusually young age or progressing in an atypical way.
Diabetes occurring in several generations of the same family.
A person who does not have typical features of type 2 diabetes.
Unexpectedly persistent insulin production despite a diagnosis of type 1 diabetes.
Diabetes associated with pancreatic, renal or endocrine abnormalities.
Blood glucose control or treatment requirements that do not fit the expected pattern.

This distinction matters because the diagnosis can influence treatment, monitoring and whether other family members should be assessed.

What are the rare genetic forms of diabetes?

Rare genetic forms of diabetes result from changes in specific genes involved in pancreatic beta-cell development, insulin production or glucose regulation. The most important groups include monogenic diabetes, which is caused by a change in a single gene and accounts for a small proportion of all diabetes cases.

Maturity-onset diabetes of the young (MODY) is one example of monogenic diabetes. It often develops at a young age and may affect several generations of a family. Neonatal diabetes is another rare genetic form, typically diagnosed within the first six months of life.

Recognising these conditions is important because their treatment can differ considerably from conventional type 1 or type 2 diabetes. A confirmed genetic diagnosis can also provide information that is relevant to relatives who may have inherited the same genetic change.

Which tests are used when the type of diabetes is uncertain?

Investigations should be guided by the clinical presentation and may include tests that establish diabetes, identify the underlying mechanism and determine whether genetic testing is appropriate.

Key investigations can include:

HbA1c and blood glucose tests: confirm and assess the severity of diabetes.
Diabetes-related autoantibody tests: help identify autoimmune type 1 diabetes.
C-peptide testing: assesses how much insulin the pancreas is still producing.
Family history assessment: identifies patterns suggesting an inherited form of diabetes.
Genetic testing: investigates suspected monogenic diabetes by looking for disease-causing genetic variants.

Genetic testing is not routinely required for everyone with diabetes. It is considered when the clinical features and family history suggest that a specific genetic form is possible, with specialist assessment helping to determine which test is appropriate.

Why can identifying the correct type of diabetes change treatment?

Accurate classification can change the most appropriate treatment because different forms of diabetes have different underlying mechanisms. Some people with genetic diabetes may respond particularly well to certain oral glucose-lowering medicines, while others require insulin or management of an associated condition.

Correct classification can also prevent someone from being treated according to an incorrect diagnosis and may clarify the expected progression of the condition. In genetic diabetes, it can additionally allow appropriately selected relatives to undergo genetic assessment.

When should you seek medical help?

Medical assessment is particularly important when diabetes develops unusually early, occurs across multiple generations, has an unexplained clinical course or does not respond as expected to treatment.

Urgent medical attention is required for severe symptoms such as vomiting, rapid breathing, marked drowsiness or significant deterioration, which can indicate a serious metabolic complication.

To discuss your symptoms and explore suitable treatment options, visit Dr Bobby Huda’s Top Doctors profile to arrange an appointment.