Normal cognitive functions in joubert syndrome

Developmental delay and subsequent impaired cognitive functions are present in almost all patients with Joubert syndrome (JS). We report on a 20-year-old woman with mild clinical signs of JS (minimal truncal ataxia and oculomotor apraxia) but typical molar tooth sign on neuroimaging, normal full scale (IQ=93), verbal (IQ=93), and performance intelligence quotient (IQ=94). Only minor difficulties in visual-spatial organization and in some executive functions could be detected. This pattern of deficits is partly reminiscent of the cerebellar cognitive affective syndrome. Her diagnosis was only reached following the diagnosis of JS in two brothers with severe cognitive impairment. Molecular investigations demonstrated a homozygous mutation in the INPP5E gene. This exceptional observation confirms that normal cognitive functions are possible in JS and corroborates the well known intrafamilial variability.