Autosomal recessive neurodegenerative disorders caused by lysosomal membrane transport defects that result in accumulation of free sialic acid (N-ACETYLNEURAMINIC ACID) within the lysosomes. The two main clinical phenotypes, which are allelic variants of the SLC17A5 gene, are ISSD, a severe infantile form, or Salla disease, a slowly progressive adult form, named for the geographic area in Finland where the kindred first studied resided.
