JOUBERT-SYNDROME REVISITED - KEY OCULAR MOTOR SIGNS WITH MAGNETIC-RESONANCE-IMAGING CORRELATION

Joubert syndrome is characterized by episodic hyperpnea and apnea, dev elopmental delay, hypotonia, truncal ataxia, ophthalmologic abnormalit ies, and vermian dysgenesis. We studied 15 patients with the diagnosis of Joubert syndrome to (1) more fully define the syndrome's clinical features, and (2) correlate the clinical features with magnetic resona nce imaging (MRI) findings. Eight of 15 patients had a history of epis odic hyperpnea and apnea. All patients had developmental delay and hyp otonia. Of the 13 patients receiving detailed neuro-ophthalmologic eva luations, three had optic nerve dysplasia, pendular nystagmus, and gaz e-holding nystagmus. All 13 patients had a normal vestibule-ocular ref lex based on head thrust, but had absent to poor ability to cancel the vestibule-ocular reflex horizontally and vertically. Twelve of 13 pat ients had impaired smooth pursuit. Twelve of 13 patients had defects i n initiation of saccades and quick phases. Two of the most consistent radiologic features were absent or hypoplastic posterior cerebellar ve rmis, and deformed midbrain and pontomesencephalic junction, which bas ed on ocular motor physiology correlate with the vestibule-ocular refl ex cancellation/pursuit defect and saccade initiation defect, respecti vely. As a result of midbrain, vermian, and superior cerebellar pedunc le abnormalities, axial neuroimaging showed a unique ''molar tooth'' a ppearance of these structures. These results indicate that Joubert syn drome results from maldevelopment of the midbrain and cerebellar vermi s, producing a pathognomonic sign on MRI.