Prenatal diagnosis
The mode of inheritance for A–T is autosomal recessive. Each parent is a carrier, meaning that they have one normal copy of the A–T gene (ATM) and one copy that is mutated. A–T occurs if a child inherits the mutated A–T gene from each parent, so in a family with two carrier parents, there is 1 chance in 4 that a child born to the parents will have the disorder. Prenatal diagnosis (and carrier detection) can be carried out in families if the errors (mutation) in an affected child's two ATM genes have been identified. The process of getting this done can be complicated and, as it requires time, should be arranged before conception.