Mental Retardation, X-Linked 90

A number sign (#) is used with this entry because X-linked mental retardation-90 (MRX90) is caused by mutation in the DLG3 (300189) gene on chromosome Xq13.

Clinical Features

Tarpey et al. (2004) reported 4 families in each of which at least 2 males had moderate to severe nonsyndromic X-linked mental retardation.

Philips et al. (2014) reported 2 unrelated Finnish families with MRX90. Three affected males in 1 family (D172) had delayed psychomotor development with speech delay, mild to moderate intellectual disability, narrow thorax, molar hypoplasia, short and upslanting palpebral fissures, high-arched palate, and hypotonia. Five males in the second family (D301) had delayed motor and language development with moderate to severe mental retardation. Three patients had ADHD, and 1 had seizures in childhood. Three had strabismus, but no other constant dysmorphic features were noted. One 60-year-old female was also affected.

Mapping

In a family segregating X-linked mental retardation, Tarpey et al. (2004) mapped the MRX locus to a 2-Mb region on Xq13, bound by markers DXS811 and DXS559.

Molecular Genetics

In affected members of 4 of 329 families with moderate to severe X-linked mental retardation, Tarpey et al. (2004) identified truncating mutations in the human DLG3 gene (300189.0001-300189.0004).

In affected members of 2 unrelated Finnish families with MRX90, Philips et al. (2014) identified 2 different splice site mutations in the DLG3 gene (300189.0005 and 300189.0006). The mutations were found by X-chromosome exome sequencing in 14 Finnish families with X-linked mental retardation.