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A Novel DLG3 Mutation Expanding the Phenotype of X-Linked Intellectual Disability Caused by DLG3 Nonsense Variants

The DLG3 gene is located at Xq13.1 and encodes SAP102, a member of the MAGUK protein family, extensively expressed in the brain and involved in synaptic function. Mutations in DLG3 are associated with a rare nonsyndromic form of X-linked intellectual disability (XLID) and have been described in 11 families to date. All affected males presented with intellectual disability, and some showed additional clinical features. The majority of female carriers were reported asymptomatic or mildly affected, due to skewed X-inactivation, rarely severely affected. We report a family, a boy and his mother, with a novel nonsense mutation in the DLG3 gene, c.1720C>T; p.Arg574*. The boy, hemizygous for the variant, showed intellectual disability, short stature due to growth hormone deficiency, dysmorphic features, and pectus excavatum. The mother, who presented with learning disabilities and borderline cognitive development, is a heterozygous carrier of the variant, which had arisen de novo. X-inactivation test was noninformative. This case report broadens the phenotypic spectrum of XLID caused by DLG3 nonsense variants. The dysmorphic features of the affected males may be more frequent than previously thought.