banner image

Inheriting AT

Inheriting AT

AT is what is called an ‘autosomal recessive’ disorder. What this means, in simple terms, is that to be affected by the condition a person has to have two copies of a particular (mutated) gene.

For this to happen, both parents have to be carriers of the ATM gene. Almost always both parents will have one normal copy and one copy with a mutation. Some people with A-T do have children and in those cases they as the parent will have two mutated copies.

Each parent passes on (at random) one or other copy of the gene. As the diagram shows, there are four possible outcomes: the child has AT (one in four chance), the child is a carrier (two in four chance) and the child does not have the mutation at all (one in four chance).

Autosomal Recessive gene


On average, one in four children born to a couple of carriers will have AT. However the chance doesn’t change if you already have a child with AT. Even if you already have one (or more) children with A-T, the chance of the next child having AT is still one in four. There are a number of families in the UK and Ireland with two and even three children with AT.

Siblings of a child with AT, who don’t have AT themselves, will each have a two out of three chance of being a carrier.