X inactivation and dystrophin studies in a t(X;12) female: evidence for biochemical normalization in Duchenne muscular dystrophy carriers.
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.
Wenger
S L
SL
Division of Medical Genetics, Children's Hospital of Pittsburgh, PA 15213-2583.
Steele
M W
MW
Hoffman
E P
EP
Barmada
M A
MA
Wessel
H B
HB
D002675:Child, Preschool; D002881:Chromosomes, Human, Pair 12; D003402:Creatine Kinase / Q000097:blood; D004261:DNA Replication; D004303:Dosage Compensation, Genetic; D016189:Dystrophin / Q000378:metabolism*; D005260:Female; D006579:Heterozygote; D006801:Humans; D009136:Muscular Dystrophies / Q000235:genetics* / Q000378:metabolism; D014178:Translocation, Genetic; D014960:X Chromosome
D016189:Dystrophin; D003402:Creatine Kinase