Alternative splicing of dystrophin mRNA complicates carrier determination: report of a DMD family.

Carrier determination is important for genetic counselling in DMD/BMD families. The detection of altered PCR amplified dystrophin mRNA fragments owing to deletions, insertions, or point mutations has increased the possibilities of carrier determination. However, problems may occur because of alternative splicing events. Here we present a family with a DMD patient characterised by a deletion of exons 45 to 54. At the mRNA level we detected a corresponding altered fragment which served for carrier determination. The mother and the sister of the patient showed the same altered dystrophin mRNA fragment as the patient and are therefore carriers. In the mother two additional altered dystrophin mRNA fragments were detectable, obviously resulting from alternative splicing in the normal allele. The grandmother and two other related females of the patient possess only the normal mRNA fragment. In a further female we detected an altered fragment owing to an mRNA deletion of exon 44. This fragment is created either by alternative splicing or a new mutation. Therefore, the carrier status of this female is still ambiguous indicating problems in carrier determination by the method of dystrophin mRNA analysis.