Family history of autism: how genes and families are linked

The NHS describes autism as a difference in how your brain develops that affects how you see and experience the world, often called a type of neurodivergence. It can affect how you communicate with and understand people, how you think, learn and pay attention, and how you respond to light, sounds, smells, tastes and touch.

Some autistic people have a learning disability and some have average or above average intelligence. Autistic people are more likely to have some physical and mental health conditions, such as epilepsy, anxiety, eating disorders or depression, and ADHD is also more common.

The National Autistic Society says autism is genetic and that most autistic people are autistic because of genes they got from their parents. If your child is autistic, it says, it is more likely that you or their other parent are also autistic. It says it is also more likely that you and your children are autistic if there are autistic people in your family.

It explains that the closer the family relationship, the more likely both people are to be autistic: identical twins have the highest likelihood, followed by full siblings, half siblings, cousins and so on. Even with identical twins, in some families one twin will be autistic and the other will not.

The charity also points out that twins, siblings or other relatives may share similar autistic traits, but only one gets a diagnosis because the other does not reach the clinical cut-off point.

According to the National Autistic Society, thousands of different genes contribute to a person being autistic, and scientists have identified only some of them. Because of this it says that genetic testing cannot predict whether a child will be autistic or not.

This means a family history is best understood as a pattern, not a test result. It does not allow anyone to say whether a particular child will or will not be autistic, and it does not mean anything is wrong with a person.

The National Autistic Society says a person is much more likely to be autistic because of genes inherited from parents than any other factor, but that in some cases other factors affect genes and contribute. It describes only two environmental factors that make it much more likely a baby will be born autistic even without getting genes from parents: the mother having rubella in the first trimester of pregnancy, and the mother taking the anti-seizure medication valproate while pregnant.

It says these are now very rare, because most people in the UK are vaccinated against rubella and strict prescribing guidelines mean valproate is not given to people who could become pregnant. The NHS states plainly that autism is not caused by vaccines or medicines.

If you take epilepsy medicine and are planning a pregnancy, do not stop it yourself. The NHS advises discussing treatment with a specialist first.

The NHS says signs might be noticed at a very young age, or not until later in life, and that autistic people differ a great deal. In young children signs can include starting to speak later than other children, not responding to their name, using eye contact less, repeating words and phrases, intense interests, enjoying repetitive actions, and being upset by changes in routine.

There can also be sensory differences, such as reacting strongly or not at all to lights, sounds, smells, tastes and textures. The NHS notes that signs can be harder to see in girls because of masking, which means not showing the signs, and that autistic boys can mask too.

The NHS advises speaking to a GP if you think your child might be autistic. If the doctor thinks your child may be autistic, they can refer them for an autism assessment and let you know about support available locally. You can also speak to a special educational needs coordinator (SENCo) at a nursery or school.

If a sibling is autistic, it is reasonable to mention that when raising concerns about a younger or older child. Support for autistic people covers many areas of life, from school to adult life, and national charities provide guidance as well.