A 13-year follow-up of Finnish patients with Salla disease.

Liisa E Paavola,Tarja T Varho,Anne M Remes,Marika J Harila,Kari Majamaa,Tapio T Korhonen

doi:10.1186/s11689-015-9116-7

Abstract

BackgroundSalla disease (SD) is a rare lysosomal storage disorder leading to severe intellectual disability. SD belongs to the Finnish disease heritage, and it is caused by mutations in the SLC17A5 gene. The aim of the study was to investigate the course of neurocognitive features of SD patients in a long-term follow-up.MethodsNeuropsychological and neurological investigations were carried out on 24 SD patients, aged 16–65 years, 13 years after a similar examination.ResultsThe survival analysis showed excess mortality among patients with SD after the age of 30 years. The course of the disease was progressive, but follow-up of SD patients revealed that motor skills improved till the age of 20 years, while mental abilities improved in most patients till 40 years of age. Verbal comprehension skills did not diminish during the follow-up, but productive speech deteriorated because of dyspraxia and dysarthria. Motor deficits were marked. Ataxia was prominent in childhood, but it was replaced by athetotic movements during the teens. Spasticity became more obvious with age especially in severely disabled SD patients.ConclusionsYounger SD patients performed better in almost every task measuring mental abilities that then seem to remain fairly constant till early sixties. Thus, the results indicate better prognosis in cognitive skills than earlier assumed. There is an apparent decline in motor skills after the age of 20 years. The early neurocognitive development predicts the later course of motor and cognitive development.

Highlights

Salla disease (SD) is a rare lysosomal storage disorder leading to severe intellectual disability
We found that the course of the disease was progressive, but follow-up of SD patients revealed that motor skills improved till the age of 20 years, while mental abilities improved in most patients till 40 years of age
There are no previous studies on mortality of SD patients, and it is not known whether such subgroups are true

Summary

Introduction

Salla disease (SD) is a rare lysosomal storage disorder leading to severe intellectual disability. SD belongs to the Finnish disease heritage, and it is caused by mutations in the SLC17A5 gene. Salla disease (SD; OMIM 604369) is a rare lysosomal storage disease that belongs to the Finnish disease heritage [1,2,3]. SD is caused by mutations in the SLC17A5 gene encoding a protein, sialin that is responsible for sialic acid transport across lysosomal membranes and that is required for normal CNS myelination [4]. All patients become intellectually disabled, but life expectancy is only slightly decreased [2]. A few patients have been reported with relatively mild symptoms [7, 14]. Dysmyelination, and corpus callosum hypoplasia are typical for all patients with SD [15,16,17]

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