[Eye movement abnormalities as a sign for the diagnosis in Niemann-Pick disease type C]

Eye movement abnormalities in familial mental retardation syndrome should lead to the suspicion of a storage disorder, including Niemann Pick disease type C, Gaucher's disease, abetalipoproteinemia and Wilson's disease. The eye movement abnormalities in our two patients were suggestive of Niemann Pick disease type C, characterized by initial loss of voluntary vertical eye movements and subsequent loss of horizontal eye movements, with preservation of the vestibulo-ocular response. The characteristics of eye movements in storage disorders are different. In Gaucher's disease a progressive horizontal gaze palsy, in abetalipoproteinemia a particular type of internuclear ophthalmoplegia with nystagmus of the adducting eye and in Wilson's disease slowing of saccades may be observed.

We evaluated two mentally retarded sisters with unclear diagnosis at the age of 34 and 27 years. At the age of 24 and 21 a vertical gaze palsy led to the diagnosis of Parinaud syndrome.

At the time of our examination both sisters were unable to perform voluntary horizontal or vertical saccades or pursuit eye movements. The vestibulo-ocular reflex was present in all directions. Optokinetic nystagmus and convergence were absent. This clinical picture led us to a suspicion of Niemann-Pick disease type C, confirmed by the presence of sea-blue histiocytes in the bone marrow biopsy.

These cases demonstrate that the pattern of eye movement disorders in some syndromes associated with mental retardation can give important clues in the determination of the diagnosis.