Christianson syndrome is an X linked syndrome associated with intellectual disability, microcephaly, seizures, ataxia and absent speech.
Presentation
Onset of symptoms is normally within the first year of life with truncal ataxia and seizures. The head is small (microcephaly). Common facial abnormalities include: Long narrow face Prominent nose Prominent jaw Open mouth
Other common features include: Uncontrolled drooling Abnormal eye movements
The associated intellectual disability is usually in the profound range, with an IQ below 40 commonly presenting.
Those affected often have a happy demeanor with frequent smiling and spontaneous laughter.
Genetics
This condition is caused by mutations in the SLC9A6 gene. This gene is located on the long arm of the X chromosome (Xq26.3). The gene encodes a sodium/hydrogen exchanger located in the endosomes. Mutations in this gene cause a decrease in the pH (overacidification) of the endosomes.
How this causes the clinical features is not known presently. The inheritance of this condition is X-linked dominant.
Diagnosis
The diagnosis may be suspected on clinical grounds. It is made by sequencing the SLC9A6 gene.
Differential diagnosis Angelman syndrome Spinocerebellar ataxia type 29
Management
There is presently no curative treatment. Management is supportive.
Epidemiology
The prevalence is estimated to be around 1 in 16,000 to 1 in 100,000, worldwide, making it a rare disease.
History
This condition was first described in 1999.Christianson AL, Stevenson RE, van der Meyden CH, Pelser J, Theron FW, van Rensburg PL, Chandler M, Schwartz CE (1999) X linked severe mental retardation, craniofacial dysmorphology, epilepsy, ophthalmoplegia, and cerebellar atrophy in a large South African kindred is localised to Xq24-q27. J Med Genet 36:759–766 The causative mutation was discovered in 2008.Gilfillan GD, Selmer KK, Roxrud I, Smith R, Kyllerman M, Eiklid K, Kroken M, Mattingsdal M, Egeland T, Stenmark H, Sjøholm H, Server A, Samuelsson L, Christianson A, Tarpey P, Whibley A, Stratton MR, Futreal PA, Teague J, Edkins S, Gecz J, Turner G, Raymond FL, Schwartz C, Stevenson RE, Undlien DE, Strømme P (2008) SLC9A6 mutations cause X-linked mental retardation, microcephaly, epilepsy, and ataxia, a phenotype mimicking Angelman syndrome. Am J Hum Genet 82:1003–10
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