The relationship between Diabetes and Genetics

Diabetes affects millions of people in the UK, and one of the most common questions asked after a diagnosis is whether it runs in families. The answer is yes — but the relationship between genetics and diabetes is more nuanced than simple inheritance.

What is diabetes?

Diabetes is a lifelong condition in which the level of glucose in the blood is too high. There are two main types, and they are genuinely different conditions rather than milder and severer versions of the same thing.

Type 1 diabetes is an autoimmune condition. The immune system destroys the insulin-producing beta cells in the pancreas, so the body produces little or no insulin. It requires insulin treatment for life and is not caused by diet or lifestyle — a persistent and unhelpful misconception.

Type 2 diabetes involves insulin resistance, where the body's cells respond poorly to insulin, often alongside declining insulin production. It accounts for around 90% of cases and is strongly influenced by weight, activity, age and ethnicity — as well as genetics.

How insulin works

Blood glucose is kept within a narrow range by homeostasis. Insulin, produced by beta cells in the pancreas, is central to this. After a meal, insulin is released and binds to insulin receptors on muscle, fat and liver cells — rather like a key in a lock. That binding opens glucose transporters, allowing glucose to leave the bloodstream and enter cells, where it is used or stored.

In type 1, there is no key. In type 2, the lock responds poorly to it.

The genetic contribution

Counter-intuitively, type 2 diabetes has a stronger genetic component than type 1. Family history is one of the most powerful predictors of type 2 risk. If both parents have type 2 diabetes, a person's lifetime risk rises substantially; identical twin concordance is higher for type 2 than for type 1.

Type 1 also has genetic contributors — particularly HLA gene variants affecting immune function — but environmental triggers appear to play a larger role in whether the condition actually develops.

Over 400 genetic variants have now been associated with type 2 diabetes, each contributing a small amount. Some of the studied genes include:

• TCF7L2 — the most strongly associated common variant, affecting insulin secretion
• MADD — involved in several cellular pathways including insulin secretion and the conversion of proinsulin to insulin
• ADCY5 — codes for a protein involved in signalling that stimulates insulin release
• GLIS3 — involved in the development of pancreatic beta cells

There is also MODY (maturity-onset diabetes of the young) — a rare form caused by a single gene variant, inherited directly, often diagnosed before age 25 and frequently mistaken for type 1 or type 2. Genetic testing matters here because MODY can sometimes be treated with tablets rather than insulin.

Genetics is not destiny

This is the crucial point. Even with a strong family history, type 2 diabetes is substantially preventable. Large trials of intensive lifestyle intervention in people at high risk have shown reductions in progression to type 2 diabetes of around 50–60% — in some studies outperforming medication.

Reducing your risk

• Maintain a healthy weight; even modest weight loss substantially reduces risk
• Aim for 150 minutes of moderate activity a week, plus strength work twice weekly
• Eat a balanced diet with plenty of fibre, and limit refined carbohydrate, sugary drinks and processed foods
• Stop smoking
• Keep alcohol within 14 units a week
• Attend your NHS Health Check if you are aged 40–74

Risk is higher, and often develops at a lower BMI, in people of South Asian, African-Caribbean and Black African heritage — screening is worth considering earlier in these groups.

Symptoms worth acting on

See your GP if you experience increased thirst, passing urine more often (especially at night), unexplained weight loss, persistent fatigue, blurred vision, or slow-healing cuts. In type 1, symptoms can develop rapidly and need urgent assessment.

Checking your risk with Rightangled

Rightangled's home blood tests can measure HbA1c, which reflects average blood glucose over the previous two to three months, alongside cholesterol and other metabolic markers. Our DNA tests assess related genetic markers. Results are reviewed by our clinical team, which includes GPhC-registered independent prescribers, with medical oversight from our doctor, Dr Abdullah.

Verify us with the General Pharmaceutical Council (registration 9011933), see our LegitScript certification, and read reviews on Trustpilot.

This article is for general information and does not replace personalised medical advice. If you have symptoms of diabetes, see your GP.