Abnormal genetic sequences (mutations) in the aristaless-related homeobox gene (ARX) have been associated with infantile spasms, Ohtahara syndrome (a severe condition related to infantile spasms), intellectual disability (mental retardation), lissencephaly (a smooth brain that lacks the folds and convolutions normally seen), agenesis of the corpus callosum (lack of the major connection between the right and left hemispheres of the brain) and genital abnormalities (so-called ambiguous genitalia). There is great variation from patient to patient, and most patients do not exhibit all of the associated symptoms/conditions. The ARX gene is located on the x-chromosome and is "x-linked". This means that the vast majority of patients with ARX-related infantile spasms are boys (although it is possible for females to have these symptoms), who either inherit the ARX mutation from an asymptomatic mother (carrier female) or have a new mutation not inherited from either parent (sporadic mutation).

There is no scientific data yet indicating that patients with ARX mutations and infantile spasms preferentially respond to any particular treatment. However, identification of an ARX mutation would prompt genetic testing of a patient's mother and could greatly impact genetic counseling. If an asymptomatic mother carries this mutation, there is a 50% chance that future sons would be affected, and a 50% chance that female children would be asymptomatic carriers of the mutation.


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