title: A 13-year follow-up of Finnish patients with Salla disease.
abstract: BACKGROUND
  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. The aim of the study was to investigate the course of neurocognitive features of SD patients in a long-term follow-up.
  
  
  METHODS
  Neuropsychological and neurological investigations were carried out on 24 SD patients, aged 16-65 years, 13 years after a similar examination.
  
  
  RESULTS
  The 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.
  
  
  CONCLUSIONS
  Younger 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.
authors.affiliation: Department of Neurology, Oulu University Hospital, P.O. Box 20, 90029 Oulu, Finland ; Department of Clinical Medicine, Neurology, University of Oulu, P.O. Box 5000, 90014 Oulu, Finland ; Department of Clinical Neurology, University of Oulu, P.O. Box 5000, 90014 Oulu, Finland ; Neural Ltd, Center of Neuropsychology, Isokatu 16 B 18, 90100 Oulu, Finland.
authors.forename: Liisa E
authors.initials: LE
authors.lastname: Paavola
authors.affiliation: Department of Neurology, Institute of Clinical Medicine, University of Eastern Finland, P.O. Box 1627, 70211 Kuopio, Finland ; Department of Neurology, Kuopio University Hospital, P.O. Box 1777, 70211 Kuopio, Finland.
authors.forename: Anne M
authors.initials: AM
authors.lastname: Remes
authors.affiliation: Neural Ltd, Center of Neuropsychology, Isokatu 16 B 18, 90100 Oulu, Finland.
authors.forename: Marika J
authors.initials: MJ
authors.lastname: Harila
authors.affiliation: The Neuropediatric Unit of Turku City Welfare Division, P. O. Box 670, 20101 Turku, Finland.
authors.forename: Tarja T
authors.initials: TT
authors.lastname: Varho
authors.affiliation: Department of Psychology, University of Turku, Turku, 20014 Finland.
authors.forename: Tapio T
authors.initials: TT
authors.lastname: Korhonen
authors.affiliation: Department of Neurology, Oulu University Hospital, P.O. Box 20, 90029 Oulu, Finland ; Department of Clinical Medicine, Neurology, University of Oulu, P.O. Box 5000, 90014 Oulu, Finland.
authors.forename: Kari
authors.initials: K
authors.lastname: Majamaa
keywords: Dysmyelination; Follow-up study; Free sialic acid storage; Neurocognitive development; Rare diseases