Molecular genetic detection of Xp21 muscular dystrophy carriers in Cyprus

Multiplex Polymerase Chain Reaction (PCR) for 18 different exons of the dystrophin gene was used to characterize the mutations in 29 Cypriot families with Duchenne or Becker Muscular Dystrophy. Deletions were detected in 21 out of 28 families from which DNA was available for an affected patient (75%). Quantitative Multiplex PCR further enabled the identification of a duplication in one of our families (3.6%). Quantitative Multiplex PCR also enabled carrier diagnosis in families where a deletion or a duplication was detectable in an affected patient. Out of 69 at-risk females examined in these families, 20 were shown by Quantitative Multiplex PCR to be carriers, including three obligatory carriers. In the remaining six families with a surviving patient, carrier diagnosis was based on haplotype analysis using microsatellite polymorphisms from the 5'- and 3'-ends of the dystrophin gene. Haplotype analysis was informative in three of the above families (10.7%). Thus, deletions or duplications were detected in 78.6% of our families with a surviving patient, while carrier diagnosis was possible in 89.3% of these families. In the single family without a surviving patient, Quantitative Multiplex PCR indicated the absence of a deletion or duplication in the mother, while haplotype analysis could not be carried out in the absence of an affected patient. The high rate of new mutations in the dystrophin gene of which only about 80% are directly detectable by Quantitative Multiplex PCR, and the difficulty of haplotype analysis in some of our families, restricts the usefulness of these techniques to about 90% of our families.