blood vessels) in the membrane that covers the white part (sclera) of the eye. Vision (ability to see objects in focus) is normal. Control of eye movement is often impaired, affecting visual functions that require fast, accurate eye movements from point to point (e.g. reading). Eye misalignments (strabismus) are common, but may be treatable. There may be difficulty in coordinating eye position and shaping the lens to see objects up close. Orthopedics Many individuals with A–T develop deformities of the feet that compound the difficulty they have with walking due to impaired coordination. Early treatment may slow progression of this deformity. Bracing or surgical correction sometimes improves stability at the ankle sufficient to enable an individual to walk with support, or bear weight during assisted standing transfers from one seat to another. Severe scoliosis is relatively uncommon, but probably does occur more often than in those without A–T. Spinal fusion is only rarely indicated. Genetics A–T is caused by mutations in the ATM (ATM serine/threonine kinase or ataxia–telangiectasia mutated) gene, which was cloned in 1995. ATM is located on human chromosome 11 (11q22.3) and is made up of 69 exons spread across 150kb of genomic DNA. 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. Looking for mutations in the ATM gene of an unrelated person (for example, the spouse of a known A–T carrier) presents significant challenges. Genes often have variant spellings (polymorphisms) that do not affect function. In a gene as large as ATM, such variant spellings are likely to occur and doctors cannot always predict whether a specific variant will or will not cause disease. Genetic counseling can help family members of an A–T patient understand what can or cannot be tested, and how the test results should be interpreted. Carriers of