Ouvrier and Billson (1988) were apparently the first to describe this entity. In the four original cases, the clinical features were as follows: (1) onset usually under 1 year of age, (2) episodes of variably sustained conjugate upward deviation of the eyes, with neck flexion (chin down) apparently compensating for the abnormal eye position, (3) downbeating saccades in attempted downgaze, (4) normal horizontal eye movements, (5) diurnal fluctuation of symptoms, (6) frequent relief by sleep, (7) exacerbation with febrile illnesses, (8) varying degrees of ataxia, (9) neurological examination usually otherwise normal, (10) absence of deterioration during long-term follow-up, (11) eventual improvement, (12) usually negative investigations, including imaging, EEG and CSF neurotransmitters. As of 2002, 49 cases have been reported. Aetiological factors have included autosomal dominant inheritance in four families, foetal exposure to sodium valproate in three cases, and structural lesions in five (hypomyelination x 2, periventricular leukomalacia, Vein of Galen malformation, pinealoma). Only a few cases have responded to L-dopa. The pathophysiology is still not understood. The outcome appears to be good in about half the cases. Ataxia, borderline cognitive abilities and residual minor oculomotor disorders are seen in the remainder.