Christianson syndrome

Christianson syndrome is a rare disorder that mainly affects the nervous system and becomes apparent in infancy. Children show delayed development, intellectual disability, an absence of speech, poor balance and coordination, and difficulty standing or walking; those who learn to walk lose the ability in childhood. Most have recurrent seizures that begin between ages one and two. Many also have a small head, a long narrow face with a prominent nose, jaw and ears, an open mouth with drooling, and abnormal eye movements, and affected children often have a happy manner with frequent smiling and laughter. It is caused by mutations in the SLC9A6 gene, which encodes the endosomal sodium/hydrogen exchanger NHE6, and is inherited in an X-linked recessive pattern, so males are affected far more often than females. It was first described in a South African family.