Salla Disease

Free sialic acid deposition disease (FSASD) or Salla disease is a lysosomal storage disorder. It is a very rare neurodegenerative disease, except in northern Finland, where it is estimated that 1 in 100 people carry a mutation causing this condition. The incidence of Salla disease worldwide is approximately one case per million people.

This disorder is caused by mutations in the SLC17A5 gene that codes for the sialin protein, which is responsible for the transport of free sialic acid out of the lysosome. Pathogenic variants in SLC17A5 disrupt the transport process, causing accumulation of large amounts of sialic acid in the lysosome and altering its function.

Salla disease can manifest in early childhood or appear progressively. When it occurs in infancy it is known as infantile Salla disease, it can develop even before birth and the symptoms are very severe. Only 150 cases have been reported worldwide, mainly in Finland and Sweden.

Progressive onset Salla disease of mild to intermediate severity, with highly variable symptomatology, is characterized by progressive cognitive dysfunction ranging from mild to severe, hypotonia, delayed psychomotor development, spasticity, epileptic seizures, hypomyelination and characteristic facial features. The presence of high levels of free sialic acid in urine may be indicative of the pathology.

There is no treatment that can cure Salla patients. The treatments used are aimed at alleviating symptoms and close follow-up by pediatricians and specialists who develop an individualized educational plan is needed. Physiotherapy is also recommended to help them acquire as much autonomy as possible and reduce the risk of injury from motor dysfunction.