FA is an inherited genetic disorder. Each of our genes is composed of half which we inherit from our mother and half from our father.

The FA genetic defect is described as autosomal recessive meaning that if a person has the abnormality only in one half of their FXN gene, they would have no symptoms, but would be a carrier. (And it’s usually only on diagnosis of an FA patient that their parents would discover, retrospectively, that they are carriers).

A child of two carriers has a 1-in-4 chance of their FXN gene being inherited from the abnormal half from their mother and the abnormal half from their father. Only in that case would they exhibit symptoms.

This visual goes some way to explaining the probability of inheritance:

So the probability for children of two carriers is that 1-in-4 would be an FA sufferer, 2-in-4 would be carriers but exhibit no symptoms and 1-in-4 would be clear of the condition altogether.