Xp21/A Translocation: a Rarely Considered Genetic Cause for Manifesting Carriers of Duchenne Muscular Dystrophy

Clinically manifesting carriers of Duchenne muscular dystrophy (DMD) are rare among the pediatric population. A standardized diagnostic procedure in supposed DMD carriers entails performing a Multiplex Ligation-dependent Probe Amplification analysis of the DMD gene first, then taking a muscle biopsy to confirm reduced dystrophin levels and/or finally a complete sequencing of the DMD gene. We describe a girl with high-elevated creatine kinase, myalgia, and cardiomyopathy. Muscle biopsy showed a dystrophic pattern and nearly absent expression of dystrophin. Diagnosis could not be confirmed by molecular genetic procedures. Because of a mild mental retardation, a chromosome analysis and molecular karyotyping were performed, revealing a balanced translocation t(X;4)(p21;q31).arr(1-22,X)x2 dn with breakpoint on the X-chromosome within an intron of the DMD gene. The inactivation of the nonderivative X-chromosome was found to be in a nonrandom pattern, resulting in a functionally balanced karyotype and thus leading to a manifesting DMD carrier in this case. Chromosome analysis should be recommended in cases of genetically unsolved DMD carriers as a part of the standard genetic procedures.