Salla Disease

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

This disorder originates from mutations in the SLC17A5 gene, which encodes the sialin protein, responsible for the transport of free sialic acid out of the lysosome. Pathogenic variants in SLC17A5 disrupt the transport process, causing the 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 presents in childhood, it is known as infantile Salla disease; it can develop even before birth, and the symptoms are very severe. Only 150 cases have been described worldwide, mainly in Finland and Sweden.  

Salla disease that appears progressively, of mild or intermediate severity, presents a very variable symptomatology, characterized by progressive cognitive dysfunction that can range from mild to severe, hypotonia, psychomotor developmental delay, spasticity, epileptic seizures, hypomyelination, and characteristic facial features. The presence of high levels of free sialic acid in urine can be an indicator of the pathology.

There is no treatment that can cure Salla patients. The treatments used are aimed at alleviating symptoms and require close monitoring by pediatricians and specialists who develop an individualized educational plan. Physiotherapy is also recommended to help them acquire the greatest possible autonomy and reduce the risk of injuries resulting from motor dysfunction.