Salla Disease Variants

Abstract

The case reports of two Swedish girls with initially pseudostationary clinical pictures, one simulating ataxic and the other dyskinetic cerebral palsy, are presented. It was eventually revealed that they had a slowly progressive encephalopathy with pronounced gross motor disability and signs of severe dyskinesia, but only mild intellectual delay. Electron microscopy of skin biopsies showed a picture identical to that in Salla disease. They had a moderately increased 5-10 fold urinary free sialic acid excretion, increased sialidase activity in lymphocytes but normal activity in cultured fibroblasts. These two Swedish cases represent variants of Salla disease, a group of conditions with probable genetic heterogeneity.

Salla disease is a newly discovered lysosomal storage disorder causing psychomotor retardation (Aula et al 1979). Recently it has been reported of 49 patients with this disease (Renlund et al 1983 a, Renlund 1984). The clinical picture of older patients can be quite variable, whereas the early manifestations seem to be more constant. So far, all cases have been reported from Finland. The diagnosis rests on a combination of clinical, morphological and laboratory findings, namely: early onset and severe psychomotor development delay, slight ataxia and transient nystagmus; later appearance of spastic paraparesis; vacuolated lymphocytes in blood smears, and storage lysosomes in skin and liver cells; and increased urinary excretion of free sialic acid. The concentration of free sialic acid in liver and cultured fibroblasts is increased (Renlund et al 1983 b). The biochemical defect of Salla disease has not yet been defined. Activities of several lysosomal enzymes, including sialidase, and of a number of other enzymes involved in the sialic acid metabolism, studied in cultured fibroblasts and liver, have so far been found to be normal (Renlund et al 1983 b). However, the sialidase activity in leucocytes has not been measured.
The purpose of this report is to present clinical and biochemical data for two unrelated Swedish patients with this disorder.

Key words

Sialic aciduria - Oligosaccharidosis - Salla disease