Mental Retardation, X-Linked 89

Clinical Features

Shoichet et al. (2003) reported a 7-year-old girl with severe developmental delay who had a de novo balanced chromosome rearrangement, t(X;7)(p11.3;q11.21). At age 2 years, she did not yet walk or speak, and she exhibited clearly delayed psychomotor development. At age 3 years 9 months, occasional convulsions, predominantly localized to the shoulders and upper back, were reported, which led to the diagnosis of myoclonic epilepsy. At age 5 years 6 months, her physical development was in the normal range. She had no dysmorphic features. Screening for inborn errors of metabolism resulted in no indication of amino acidopathies or organic acidurias.

Shoichet et al. (2003) reported 2 male probands with X-linked mental retardation without dysmorphic features or additional neurologic abnormalities. The proband in 1 family had delayed early milestones and at the age of 5 years was functioning at an intellectual level of age 3 years. He exhibited language retardation, avoided social contact, and was hyperactive. Both of the mother's brothers were affected but further clinical data were not available. The proband in the other family reached early milestones within the normal time frame, but exhibited a severe language delay. At age 10 years, he was unable to read, had essentially no acquisition of mathematics skills, and required special education. He had mood disorders, with both hyperactivity and aggressiveness.

History

In a 7-year-old girl with severe mental retardation and a de novo balanced translocation t(X;7)(p11.3;q11.21), Shoichet et al. (2003) cloned the DNA fragment that contained the X chromosomal and the autosomal breakpoint. In silico sequence analysis demonstrated that the ZNF41 gene was disrupted. Expression studies indicated that ZNF41 transcripts were absent in the patient cell line, suggesting that the mental disorder in this patient resulted from loss of functional ZNF41. Moreover, screening of a panel of patients with nonsyndromic MRX led to the identification of ZNF41 mutations in affected members of 2 unrelated families (314995.0001-314995.0002).

Piton et al. (2013) found the mutations in ZNF41 identified by Shoichet et al. (2003) in a total of 7 males in the NHLBI Exome Variant Server; they also found truncating ZNF41 variants in 1 male and 1 female in that database. Based on these findings, as well as a lack of reported ZNF41 mutations since 2003, Piton et al. (2013) classified the involvement of ZNF41 mutations in mental retardation as highly questionable.