intellectual disability, X-linked 1 (Monarch Disease Ontology entry MONDO_0010656) is an X-linked dominant condition caused by mutation(s) in the IQSEC2 gene, encoding IQ motif and SEC7 domain-containing protein 2. It is characterized by substantially impaired intellectual functioning and behavioral abnormalities. Also known as: IQSEC2-related disorder, IQSEC2-related syndromic intellectual disability, MRX, MRX1, MRX78, intellectual developmental disorder, X-linked 1, X-linked dominant, mental retardation, X-linked 1, mental retardation, X-linked 18.