Vertical saccade palsy: a presenting sign of Niemann-Pick type IIS

An 8 year old sister of a patient undergoing investigations for Niemann-Pick type IIS was observed to have mild difficulties in making downward saccades. She had no other symptoms apart from longstanding mild learning difficulties. Detailed eye movement assessment, using horizontal and vertical electro-oculography and video monitoring, revealed normal horizontal but abnormal vertical eye movements. Vertical downward saccades were absent and could only be achieved by mobilizing the bead to allow for headthrusts. Upward saccades were present at initial presentation, however a subsequent recording after 10 months revealed an inability to make upward saccades unless accompanied by blinks. Vertical optokinetic nystagmus was absent, although vertical smooth pursuit and vestibular ocular reflex were present. Cultured skin fibroblasts showed defective cholesterol esterification which confirmed the diagnosis of Niemann-Pick type IIS (previously known as type C). Vertical saccade palsy has been described as part of the neurological deficits, however it has not been previously reported as the presenting sign of Niemann-Pick type IIS.