Salla disease

Salla disease (also called sialic acid storage disease or Finnish type sialuria) is an autosomal recessive lysosomal storage disease characterized by early physical impairment and mental retardation. First described in 1979, Salla disease is named after Salla, a municipality in Finnish Lapland. Salla disease is one of 40 Finnish heritage diseases and affects approximately 130 individuals, mainly from Finland and Sweden.

Diagnosis
Individuals with Salla disease may present with nystagmus in the first months of life as well as hypotonia, reduced muscle tone and strength, 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.

Pathophysiology


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.

Life Expectancy
The life expectancy for individuals with Salla disease is between the ages of 50 and 60.

Diagnosis and Testing
A diagnosis of this disorder can be made by measuring urine to look for elevated levels of free sialic acid. Prenatal testing is also available for known carriers of this disorder.

Treatment
There is no cure for Salla Disease. Treatment is limited to controlling the symptoms of this disorder. Anti-convulsant medication may control seizure episodes. Physical therapists can assist an affected individual to build muscle strength and coordination, and speech therapists may assist the affected individual in improving his or her speech.