Third, weak CASK-LOF mutations, i.e., allowing considerable retention of function, cause X-linked recessive ID in males [10, 34, 52, 111, 124, 139, 150] with normal brain architecture (at MRI resolution) and variable features, including nystagmus, disruptive behavior, autism, constipation, facial dysmorphic, short stature, and microcephaly or relative macrocephaly. The gene discussed is CASK; the disease is microcephaly.