The diagnosis and frequency of X-linked conditions in a cohort of moderately retarded males with affected brothers

Am J Med Genet. 1983 Apr;14(4):713-24. doi: 10.1002/ajmg.1320140413.


An epidemiological study was carried out on the group of moderately retarded brothers (IQ, 30-55) identified by Turner and Turner [1974]. Of the original 58 sets of brothers, 54 sets (now 17 to 32 years old) were traced; another four sets (missed in the earlier survey) were added. Forty-five of the 58 pairs were diagnosed as having nonspecific X-linked mental retardation (MR) giving an overall frequency of 5.57 moderately retarded males/10,000 male births. In 12 of the 45 families, affected males had the fragile(X) and macroorchidism; six had macroorchidism alone, giving a frequency of 2.8 moderately retarded males with X-linked MR and macroorchidism +/- the fragile(X) per 10,000 males. Corresponding heterozygote frequencies are 7.34 and 3.65/10,000 females respectively. A new subgrouping of nonspecific X-linked mental retardation is described in six families: X-linked MR, macroorchidism without the fragile(X). Three other X-linked conditions were identified: in one family, the Coffin-Lowry syndrome, in another, Duchenne muscular dystrophy, and in two families X-linked MR and muscle atrophy. Half (56%) of the obligatory carriers of fra(X)-MR in this study were dull to mildly retarded. The mildly retarded heterozygotes had a significantly higher percentage of fra(X) expressing lymphocytes as compared to the intellectually normal heterozygotes. When the three types of nonspecific X-linked MR for which population frequencies were calculated were considered together, half of the obligatory carriers (46%) were dull or mildly retarded, thus confirming that this condition is a significant cause of mild intellectual handicap in females.

Publication types

  • Comparative Study

MeSH terms

  • Adolescent
  • Adult
  • Epidemiologic Methods
  • Female
  • Fragile X Syndrome / genetics
  • Genetic Linkage*
  • Heterozygote
  • Humans
  • Intellectual Disability / genetics*
  • Male
  • Pedigree
  • Sex Chromosome Aberrations / diagnosis
  • Sex Chromosome Aberrations / epidemiology
  • Sex Chromosome Aberrations / genetics*
  • Sex Chromosomes*
  • Testis / abnormalities
  • X Chromosome*