PHENOTYPIC VARIATION AND MAGNETIC-RESONANCE-IMAGING (MRI) IN SALLA DISEASE, A FREE SIALIC-ACID STORAGE DISORDER

Salla disease (SD) is a recessively inherited lysosomal storage disord er particularly common in the Finnish population. Patients with SD are normal at birth, but develop psychomotor delay and ataxia during the first year of life. Phenotypic variation of SD is wide, ranging from s everely disabled children to mentally retarded adults capable of livin g under sheltered conditions. In the present study four unusually seve rely affected patients were investigated by detailed clinical examinat ion, magnetic resonance imaging (MRI) and analysis of the excretion of free sialic acid in urine. MRI study, reported here for the first tim e, revealed a similarly defective myelination pattern in seven patient s. The myelination process seemed to cessate at the level of an infant of a few months of age. Genetic linkage study of the families of the severely affected patients suggested linkage to the recently discovere d SD locus on the long arm of chromosome 6. Locus heterogeneity theref ore is an unlikely explanation of the phenotypic variation in SD.