
Christianson syndrome

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 
Other common features include
The associated intellectual disablity is usually in the profound range.
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 rise in the pH 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. 
Management.
There is presently no curative treatment. Management is supportive.
Epidemiology.
The prevalence is not known but this is considered to be a rare disease.
History.
This condition was first described in 1999. The causative mutation was discovered in 2008.