A very rare form of syndromic intellectual deficit characterized by microcephaly, severe developmental delay or regression, hypotonia, abnormal movements, and early-onset seizures. The disease is Monarch Disease Ontology identifier MONDO_0010278 (Christianson syndrome). Also known as: MRXSCH, X-linked Angelman-like syndrome, X-linked intellectual disability, South African type, X-linked intellectual disability-craniofacial dysmorphism-epilepsy-ophthalmoplegia-cerebellar atrophy syndrome, intellectual developmental disorder, X-linked syndromic, Christianson type, intellectual disability, X-linked syndromic, Christianson type, intellectual disability, microcephaly, epilepsy, and ataxia syndrome, mental retardation, X-linked syndromic, Christianson type.