Expansion of the ARX spectrum.

We present four patients with ARX mutations and widely variant clinical presentations. Case 1, a female with a known ARX mutation has refractory infantile spasms and severe mental retardation. Case 2, a male presented with a neurodegenerative disorder and has a known ARX mutation likely de novo as mother is not a carrier. Cases 3 and 4, two siblings with a novel variant in ARX, which is not clearly pathogenic, have developmental delay. One of the siblings had a diagnosis of autistic spectrum disorder, failure to thrive with severe feeding difficulties, intracranial hemorrhage, and seizures. There are very few affected females with ARX related infantile spasms. These cases expand the known phenotype of this emerging condition.