Salla disease

Salla disease (SD) is an autosomal recessive[2] lysosomal storage disease characterized by early physical impairment and intellectual disability. It was first described in 1979,[3] 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.

Salla disease
Other namesSialic acid storage disease or Finnish type sialuria[1]
Sialic acid
SpecialtyNeurology, endocrinology 

Presentation

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.[4] 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.[5]

Genetics
Salla disease has an autosomal recessive pattern of inheritance.

SD is caused by a mutation in the SLC17A5 gene, located at human chromosome 6q14-15.[2][6] 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.

The disease is inherited in an autosomal recessive manner.[2] This means the defective gene responsible for the disorder is located on an autosome (chromosome 6 is an autosome), and two copies of the defective gene (one inherited from each parent) are required in order to be born with the disorder. The parents of an individual with an autosomal recessive disorder both carry one copy of the defective gene, but usually do not experience any signs or symptoms of the disorder.

Diagnosis

A diagnosis of this disorder can be made by measuring urine to look for elevated levels of free sialic acid.[7] 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.

Prognosis

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

See also

References
  1. Online Mendelian Inheritance in Man (OMIM): 604369
  2. Aula N, A. P.; Aula, P. (August 2006). "Prenatal diagnosis of free sialic acid storage disorders (SASD)". Prenatal Diagnosis. 26 (8): 655–658. doi:10.1002/pd.1431. PMID 16715535. S2CID 20586318.
  3. Aula, P; Autio, S; Raivio, Ko; Rapola, J; Thodén, Cj; Koskela, Sl; Yamashina, I (Feb 1979). ""Salla disease": a new lysosomal storage disorder" (Free full text). Archives of Neurology. 36 (2): 88–94. doi:10.1001/archneur.1979.00500380058006. ISSN 0003-9942. PMID 420628.
  4. Autio-Harmainen H, Oldfors A, Sourander P, Renlund M, Dammert K, Simila S (1988). "Neuropathology of Salla disease". Acta Neuropathol. 75 (5): 481–490. doi:10.1007/BF00687135. PMID 3287834. S2CID 39839325.
  5. Strehle EM (2003). "Sialic acid storage disease and related disorders". Genet Test. 7 (2): 113–121. doi:10.1089/109065703322146795. PMID 12885332.
  6. Online Mendelian Inheritance in Man (OMIM): 604322
  7. Kleta R, Morse RP, Orvisky E, Krasnewich D, Alroy J, Ucci AA, Bernardini I, Wenger DA, Gahl WA (2004). "Clinical, biochemical, and molecular diagnosis of a free sialic acid storage disease patient of moderate severity". Mol Genet Metab. 82 (2): 137–143. doi:10.1016/j.ymgme.2004.03.001. PMID 15172001.
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