The eye movements of four patients with ataxia telangiectasia (AT), three of whom had an unusual neurological presentation, were studied. All had striking abnormalities of saccadic generation with markedly hypometric saccades, increased saccadic latency, but normal saccadic velocity. Three patients used head thrusts to aid refixation. In addition, there was absence of smooth pursuit and optokinetic nystagmus, and hyperactive vestibular responses. Two of the four patients had, in addition, periodic alternating nystagmus. This combination of an ocular motor apraxia with superadded cerebellar ocular motor abnormalities, and possibly periodic alternating nystagmus, should strongly suggest the diagnosis of AT, even if the clinical syndrome is otherwise atypical. Key Words Ataxia telangiectasia-Ocular motor apraxia-Eye movements in cerebellar disease.
Ataxia telangiectasia (AT) is an autosomal recessive disorder characterised by cutaneous and conjunctival telangiectasia and a progressive neurological syndrome comprising cerebellar ataxia, choreo-athetosis, peripheral neuropathy, and abnormal eye movements. Additional features include mental and growth retardation, and a predisposition to cutaneous and respiratory infections due to deficiencies of both humoral and cell-mediated immunity (1-3). Ten to twenty percent of patients develop malignancy which is usually of lymphoreticular origin. The majority of patients are chairbound in their teens, and survival beyond the third decade of life is unusual. Increased serum concentrations of a-fetoprotein are almost universal (43).
Recently, it has become clear that AT is clinically heterogeneous (&lo), several ' A videotape segment accompanies this article.