Beta-mannosidosis: a new cause of spinocerebellar ataxia.

Beta-mannosidosis (OMIM 248510) is an inborn lysosomal storage disorder caused by deficiency of beta-mannosidase activity. This enzyme is encoded by a single gene (MANBA), located on chromosome 4q22-25. This autosomal recessive disorder is characterized by a wide range of symptoms including mental retardation, behavioural problems, hearing loss, recurrent respiratory infections, angiokeratoma, facial dysmorphism, skeletal deformation, seizures, hypotonia, demyelinating polyneuropathy, and hepatosplenomegaly. The age of symptom onset is variable. We describe a 14-year clinical follow-up of a patient with beta-mannosidase deficiency with symptoms of mental retardation, progressive spasticity and cerebellar ataxia, a clinical spectrum that so far has never been reported in beta-mannosidosis. A novel mutation in the MANBA gene was found in our patient. Evoked potentials were in favour of a demyelinating pathology of the central nervous system. Serial MRI showed generalized cortical and subcortical atrophy in the absence of white matter changes suggesting an additional axonal pathophysiological component.