Individuals with Salla disease may present with nystagmus in the first months of life as well as hypotonia and cognitive impairment. The most severely impaired children do not walk or acquire language, but the typical patient learns to walk and speak and has normal life expectancy. The MRI shows arrested or delayed myelination.
The disorder is caused by a mutation in chromosome 6 (a recessive genetic trait in the gene SLC17A5, the locus of which is 6q14-15). This gene codes for sialin, a lysosomal membrane protein that transports the charged sugar, N-acetylneuraminic acid (sialic acid), out of lysosomes. The mutation causes sialic acid to build up in the cells.
First described in 1979, Salla disease is named after Salla, a municipality in Finnish Lapland. It is one of nearly 40 diseases that make up the Finnish disease heritage. The majority of Salla disease patients in Finland live in Salla or neighboring municipalities, with other patients living abroad.