KCNK9 imprinting syndrome is an extremely rare genetic disorder characterized by a variety of symptoms including distinctive facial features, varying degrees of intellectual disability, and congenital hypotonia. The KCNK9 imprinting syndrome is caused by an alteration in the maternal copy of the KCNK9 gene. The paternal copy of the gene is imprinted allowing only maternal KCNK9 expression. An alteration in the paternal copy of the KCNK9 gene is not believed to be associated with disease. KCNK9 imprinting syndrome has been described in only a few families worldwide. The incidence and prevalence of the disorder is unknown, and a registry has been established to learn more about this disorder. It is likely that some people with this disorder go undiagnosed or misdiagnosed, making it difficult to determine the true frequency of KCNK9 imprinting syndrome in the general population. Molecular genetic testing is available through specialized laboratories, and most cases are diagnosed by whole exome sequencing. To date, a specific amino acid change (p.G236R) has been detected in the KCNK9 gene most likely as a recurrent de novo event in families. Recently, a single patient with a p.Ala237Asp alteration has also been described.
KCNK9