Family history of type 1 diabetes: how much does it raise risk?

The NHS says type 1 diabetes is a condition where your body cannot make a hormone called insulin. Insulin helps your body use glucose for energy, and without it the level of glucose in your blood becomes too high. People with type 1 diabetes need to take insulin every day.

It is caused by a problem with the immune system, which makes it an autoimmune condition. Diabetes UK explains that the body has destroyed the insulin-producing beta cells in the pancreas, and that this can happen over years. It is different from type 2 diabetes, which is more common in older people and people who are overweight.

Diabetes UK says that although the exact cause of type 1 diabetes is not known, family history can increase your risk, as a number of genes are linked to it. It then makes an important qualification: genes on their own do not cause diabetes, because most people with type 1 do not have a family history of it at all.

The charity describes the practical size of the effect in plain terms: if someone in your family has type 1 diabetes, there is a slightly higher chance of you or your child developing the condition, but many people with type 1 do not have any family with the condition.

The NHS adds a second kind of family link. You are more likely to get type 1 diabetes if you have other problems with your immune system, or if others in your family have type 1 diabetes or other autoimmune conditions.

Diabetes UK says scientists think some things in the environment, such as viruses, play a role in triggering type 1 diabetes. Type 1 diabetes is thought to develop due to a combination of genetics and other factors that are not yet fully understood, and the charity says there is nothing to indicate that lifestyle plays a part.

That is a contrast with type 2 diabetes. The NHS says you can sometimes reduce your risk of type 2 diabetes with lifestyle changes, but it is not possible to prevent type 1 diabetes. Parents sometimes wonder whether something they did caused their child's type 1 diabetes. Diabetes UK says there is nothing you could have done to prevent it.

The NHS says the most common symptoms are peeing more than usual, especially at night, feeling very thirsty and drinking more than usual, feeling very tired, and losing weight without trying. The easiest way to remember them is the 4 Ts: toilet, thirsty, tired, thinner. Children may have heavier nappies or start wetting the bed.

Other symptoms can include blurred vision, breath that smells sweet or fruity, cuts that heal slowly, and frequent infections such as thrush. The NHS says symptoms develop quickly, over a few days or weeks. Type 1 diabetes usually starts in children and young adults but can happen at any age.

The NHS says to ask for an urgent GP appointment or get help from NHS 111 if you think you or your child has type 1 diabetes. Call 999 or go to A&E if there has been peeing more, thirst and tiredness together with symptoms getting worse quickly, stomach pain, diarrhoea or being sick, feeling sleepy or confused, or breathing faster and more deeply than usual.

These could be signs of diabetic ketoacidosis, which the NHS says can be life threatening if not treated quickly. If untreated, type 1 diabetes can lead to this serious condition.

If a GP thinks you or your child could have type 1 diabetes, the NHS says they will do a finger-prick test to check for high blood glucose and may test a sample of pee. If the tests suggest diabetes, you will see a specialist in hospital to start treatment, usually the same day.

Diabetes UK says there is a type 1 diabetes test that helps doctors know who is at high risk, but that screening is currently only available for children aged 3 to 13 in the UK as part of a research study. It also advises that if you have been diagnosed under 25 and have other family members with diabetes, you should speak to your diabetes team about genetic testing to rule out rarer types such as MODY.