X inactivation and dystrophin studies in a t(X;12) female: evidence for biochemical normalization in Duchenne muscular dystrophy carriers

Am J Med Genet. 1992 Aug 1;43(6):1012-5. doi: 10.1002/ajmg.1320430619.


A 4-year-old girl was identified with high creatine kinase (CK) values, and mild muscle weakness in a limb-girdle distribution. Results of dystrophin analysis of the muscle biopsy were consistent with a manifesting heterozygote for Duchenne muscular dystrophy. In peripheral lymphocytes she had a t(X;12) (p21.2;q24.33). Late DNA replication studies demonstrated inactivation of the normal X chromosome in 99.4% of cells. Dystrophin immunofluorescence showed 64% dystrophin-negative muscle fibers. Dystrophin content of muscle by immunoblot was approximately 5% of normal. The discordance between the percent of normal X inactivation and percent of dystrophin-negative cells may be explained by compensatory protection of dystrophin by rare nuclei with the normal X active in multi-nucleated muscle fibers with shared cytoplasm.

Publication types

  • Case Reports

MeSH terms

  • Child, Preschool
  • Chromosomes, Human, Pair 12
  • Creatine Kinase / blood
  • DNA Replication
  • Dosage Compensation, Genetic*
  • Dystrophin / metabolism*
  • Female
  • Heterozygote
  • Humans
  • Muscular Dystrophies / genetics*
  • Muscular Dystrophies / metabolism
  • Translocation, Genetic
  • X Chromosome


  • Dystrophin
  • Creatine Kinase