Christianson syndrome

Christianson syndrome is an X-linked syndrome associated with intellectual disability, microcephaly, seizures, ataxia, and absent speech.^[1][2] Many individuals with this condition have a happy demeanor with frequent smiling and unprovoked laughter, similar to those with Angelman syndrome.^[1] Christianson syndrome is caused by mutations in the SLC9A6 gene, which is located within the q24-q27 interval of the X chromosome.^[1] There appears to be a range of phenotypes in carrier females, from intellectual disability to absence of symptoms.^[1][2]

In 1999, Christianson et al. described a 5-generation South African family with X-linked mental retardation, comprising 16 affected males and 10 carrier females. In 2008, Gilfillan et al. reported 3 additional families with the disorder: a Norwegian family with 3 affected males; a Swedish family with 1 affected son; and a family from the United Kingdom with 3 affected boys. In 2010, Schroer et al. reported a large family with 6 additional confirmed cases.^[1]

In 2014, 12 additional families with boys affected by Christianson syndrome were identified in a large study.  At present medical researchers believe Christianson syndrome may be one of the most common causes of X-linked brain development disorders.  Medical researchers estimate the condition may affect between 1 in 16,000-100,000 people worldwide.^[3]