Christianson syndrome

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. 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 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. ==References==