Impaired mental functioning occurs as an isolated feature or as part of many syndromes listed in the X-linked catalog. Mental retardation that is not associated with other distinguishing features is referred to as 'nonspecific.'
- Classification ... Impaired mental functioning occurs as an isolated feature or as part of many syndromes listed in the X-linked catalog. Mental retardation that is not associated with other distinguishing features is referred to as 'nonspecific.' - Classification Opitz and Sutherland (1984) reported on a conference in which fragile X mental retardation and X-linked mental retardation of numerous other types were discussed. The report contains a rather comprehensive discussion by Opitz of the nosology of X-linked mental retardation. Mulley et al. (1992) reviewed nomenclature guidelines for X-linked mental retardation. Raymond (2006) reviewed the diagnosis and classification of X-linked mental retardation and discussed the phenotypes associated with genes causing syndromic and nonsyndromic mental retardation.
Suthers et al. (1988) reported a large family in which multiple males spanning several generations had nonsyndromic X-linked mental retardation. Two developed psychiatric problems and 1 had infrequent seizures. Carrier females were 'less academically able compared to their ... Suthers et al. (1988) reported a large family in which multiple males spanning several generations had nonsyndromic X-linked mental retardation. Two developed psychiatric problems and 1 had infrequent seizures. Carrier females were 'less academically able compared to their non-carrier sibs' (Shoubridge et al., 2010). Shoubridge et al. (2010) provided follow-up of a family with X-linked mental retardation reported by Gedeon et al. (1994) as MRX18. Affected males had moderate to severe intellectual disability, and some had seizures. Carrier females had varying levels of intellectual disability. Some affected individuals had brachycephaly, large ears, and a fixed flexion deformity of the elbows. Three males had autistic features, and most had delayed language skills.
In affected members of 4 unrelated families with X-linked nonsyndromic mental retardation (MRX1; 309530), Shoubridge et al. (2010) identified 4 different hemizygous mutations in the IQSEC2 gene (300522.0001-300522.0004). Two of the families had been reported by Suthers et ... In affected members of 4 unrelated families with X-linked nonsyndromic mental retardation (MRX1; 309530), Shoubridge et al. (2010) identified 4 different hemizygous mutations in the IQSEC2 gene (300522.0001-300522.0004). Two of the families had been reported by Suthers et al. (1988) and Gedeon et al. (1994). Some carrier females had learning disabilities. The authors suggested that a defect in the GTP-binding activity of mutant IQSEC2 may influence the regulation of actin cytoskeleton organization and neuronal development in the brain.
Herbst (1980) reviewed 24 pedigrees ascertained in British Columbia; cytogenetic studies were not done. Based on this study, Herbst and Miller (1980) calculated an incidence of X-linked mental retardation of 1.83 per 1,000 live male births and a ... Herbst (1980) reviewed 24 pedigrees ascertained in British Columbia; cytogenetic studies were not done. Based on this study, Herbst and Miller (1980) calculated an incidence of X-linked mental retardation of 1.83 per 1,000 live male births and a carrier frequency of 2.44 per 1,000 live female births. Assuming a mutation rate for X-linked loci of 3 to 9 x 10(-5) and a fitness of zero for affected males, they estimated that 7 to 19 genes cause nonspecific mental retardation. Included in their pedigrees were some having marXq28 ('fragile X'); based on literature review, they estimated that one-half of X-linked mental retardation is associated with marXq28, leaving a substantial proportion of cases which could be labeled 'nonspecific.'