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X-linked mental retardation type Christianson - SLC9A6

Clinical Features

Mutations in the SLC9A6 gene are inherited via the X chromosome; in affected families, it is primary male family members that develop the disease. The clinical symptoms are very similar to those of Angelman Syndrome, especially in infancy:

• Severe developmental delay
• Little or no speech development
• Epilepsy
• Ataxia
• Hyperactivity, joyful mood, spontaneous laughing
• Muscle hypotonia, also of the face muscular (drooling)
• Small stature

Some patients show developmental regression as the disease progresses. CMRT may reveal progressive cerebellar atrophy; spectroscopy shows an elevated signal for glutamate/glutamine in the basal ganglia. Patients are very thin, especially in their teen and adult years; they may also suffer from progressive scoliosis.

Genetic Information

The SLC9A6 gene is located on the long arm of the X chromosome and possibly takes part in cellular processes similar to those of the UBE3A gene, in which mutations cause Angelman Syndrome.
The disease follows an X chromosomal pattern of inheritance. Female carriers normally show no clinical symptoms; an uneven X-inactivation is not found.

Prevalence

No reliable data so far

Diagnostic