a slowly progressive multisystem disorder with the following manifestations: ataxia appearing with the onset of walking; telangiectases of the conjunctiva and skin of the face, neck, and ears; athetosis and nystagmus; and recurrent infections of the respiratory system caused by immunoglobulin deficiencies. Due to an autosomal recessive trait, with major pathological changes involving the cerebellar cortex, posterior columns, spinocerebellar tracks, anterior horn cells, dorsal roots, and peripheral nerves. Approximately 70% of the patients have an IgA deficiency concomitant with decreased T helper cell function. There are numerous chromosome breaks and alpha-fetoprotein levels in the sera are usually elevated. Syn: ataxia telangiectasia syndrome, Louis-Bar syndrome.