Search tips
Search criteria 


Logo of jmedgeneJournal of Medical GeneticsVisit this articleSubmit a manuscriptReceive email alertsContact usBMJ
J Med Genet. 1990 October; 27(10): 627–631.
PMCID: PMC1017241

Fragile Xq27.3 in female heterozygotes for the Martin-Bell syndrome.


X inactivation studies have been carried out on lymphocytes from eight unrelated females heterozygous for the Martin-Bell syndrome. Four of these carriers were of normal IQ and four were mentally handicapped. When BrdU was used to differentiate between the active and inactive X chromosome an average of 55% of fra(X) were active in the retarded subjects, but only 27% were active in those of normal IQ. When 3H thymidine was used to differentiate between the active and inactive X chromosome, an average of 58% of mitoses from handicapped subjects and 33% of mitoses from normal subjects showed an active fra(X) in informative cells. These results are compared with previously published studies and it is concluded that the number of inactive fra(X) chromosomes calculated as a proportion of all cells scored is the same in mentally normal and mentally retarded subjects. However, the number of active fra(X) chromosomes is consistently higher in the retarded than in the normal females.

Full text

Full text is available as a scanned copy of the original print version. Get a printable copy (PDF file) of the complete article (686K), or click on a page image below to browse page by page. Links to PubMed are also available for Selected References.

Selected References

These references are in PubMed. This may not be the complete list of references from this article.
  • Sherman SL, Morton NE, Jacobs PA, Turner G. The marker (X) syndrome: a cytogenetic and genetic analysis. Ann Hum Genet. 1984 Jan;48(Pt 1):21–37. [PubMed]
  • Nussbaum RL, Ledbetter DH. Fragile X syndrome: a unique mutation in man. Annu Rev Genet. 1986;20:109–145. [PubMed]
  • Jacobs PA, Glover TW, Mayer M, Fox P, Gerrard JW, Dunn HG, Herbst DS. X-linked mental retardation: a study of 7 families. Am J Med Genet. 1980;7(4):471–489. [PubMed]
  • Lyon MF. X-chromosome inactivation and developmental patterns in mammals. Biol Rev Camb Philos Soc. 1972 Jan;47(1):1–35. [PubMed]
  • Migeon BR, Moser HW, Moser AB, Axelman J, Sillence D, Norum RA. Adrenoleukodystrophy: evidence for X linkage, inactivation, and selection favoring the mutant allele in heterozygous cells. Proc Natl Acad Sci U S A. 1981 Aug;78(8):5066–5070. [PubMed]
  • Knoll JH, Chudley AE, Gerrard JW. Fragile (X) X-linked mental retardation. II. Frequency and replication pattern of fragile (X)(q28) in heterozygotes. Am J Hum Genet. 1984 May;36(3):640–645. [PubMed]
  • Uchida IA, Joyce EM. Activity of the fragile X in heterozygous carriers. Am J Hum Genet. 1982 Mar;34(2):286–293. [PubMed]
  • Howell RT, McDermott A. Replication status of the fragile X chromosome, fra(X)(q27), in three heterozygous females. Hum Genet. 1982;62(3):282–284. [PubMed]
  • Paul J, Froster-Iskenius U, Moje W, Schwinger E. Heterozygous female carriers of the marker-X-chromosome: IQ estimation and replication status of fra(X)(q). Hum Genet. 1984;66(4):344–346. [PubMed]
  • Tuckerman E, Webb T, Bundey SE. Frequency and replication status of the fragile X, fra(X)(q27-28), in a pair of monozygotic twins of markedly differing intelligence. J Med Genet. 1985 Apr;22(2):85–91. [PMC free article] [PubMed]
  • Tuckerman E, Webb T, Thake A. Replication status of fragile X(q27.3) in 13 female heterozygotes. J Med Genet. 1986 Oct;23(5):407–410. [PMC free article] [PubMed]
  • Tuckerman E, Webb T. The inactivation of the fragile X chromosome in female carriers of the Martin Bell syndrome as studied by two different methods. Clin Genet. 1989 Jul;36(1):25–30. [PubMed]
  • Wilhelm D, Froster-Iskenius U, Paul J, Schwinger E. Fra(X) frequency on the active X-chromosome and phenotype in heterozygous carriers of the fra(X) form of mental retardation. Am J Med Genet. 1988 May-Jun;30(1-2):407–415. [PubMed]
  • Fryns JP, Kleczkowska A, Kubień E, Petit P, Van den Berghe H. Inactivation pattern of the fragile X in heterozygous carriers. Hum Genet. 1984;65(4):400–401. [PubMed]
  • Fryns JP, Van den Berghe H. Inactivation pattern of the fragile X in heterozygous carriers. Am J Med Genet. 1988 May-Jun;30(1-2):401–406. [PubMed]
  • Nielsen KB, Tommerup N, Poulsen H, Jacobsen P, Beck B, Mikkelsen M. Carrier detection and X-inactivation studies in the fragile X syndrome. Cytogenetic studies in 63 obligate and potential carriers of the fragile X. Hum Genet. 1983;64(3):240–245. [PubMed]
  • Uchida IA, Freeman VC, Jamro H, Partington MW, Soltan HC. Additional evidence for fragile X activity in heterozygous carriers. Am J Hum Genet. 1983 Sep;35(5):861–868. [PubMed]
  • Schempp W, Meer B. Cytologic evidence for three human X-chromosomal segments escaping inactivation. Hum Genet. 1983;63(2):171–174. [PubMed]

Articles from Journal of Medical Genetics are provided here courtesy of BMJ Publishing Group