Salla disease (also called sialic acid storage disease) is a very rare, often slowly progressing, recessive lysosomal storage disease that leads to a neurodegenerative disorder. It is most common in people of Finnish ancestry. Wikipedia NIH
Salla disease is caused by mutations in the SLC17A5 gene. [PMID 10581036] 23andMe tests for the R39C mutation in SLC17A5 as i5012634.