The Syndrome of Infantile-Onset Saccade Initiation Delay

Abstract

Infantile-onset saccade initiation delay (ISID), also known as congenital ocular motor apraxia, is characterized by the inability to initiate volitional horizontal saccades. Other abnormalities including developmental delay and ataxia have been reported. The frequency of these abnormalities is unknown. We performed a detailed review of the medical literature to quantify features of ISID. We searched the English medical literature for articles related to ISID from 1952 to 2010. Whenever possible, patients were excluded if they had acquired SID, Joubert syndrome or neurodegenerative conditions. The minimum prevalence was calculated for each abnormality. Sixty-six articles with information on 288 patients were included in the analysis. Head thrusts were reported in 84.7%. Blinks without head thrusts were used to initiate saccades in 41%. The fast phases of the optokinetic response and vestibulo-ocular reflex were impaired in 69.8% and 34.4% respectively. Smooth ocular pursuit was abnormal in 33%. Global developmental delay occurred in 41.3%, speech or language delay in 36.5%, cognitive delay in 17%, hypotonia in 35.8%, motor delay in 48.6%, and ataxia/clumsiness in 49.3% of patients. Neuroimaging was performed on 197 patients and was normal in 39.1%. Abnormalities involved the cerebellum (24.9%), cerebrum (15.7%), other infratentorial structures (11.7%), and corpus callosum (6.1%). Infantile-onset saccade initiation delay is frequently associated with deficits in reflexive saccades and less frequently with impaired smooth ocular pursuit. Developmental delay, hypotonia, and ataxia occur frequently in ISID, suggesting more global brain impairment and not just a saccadic disorder.