13 families and 34 women at risk of being carriers of Duchenne and Bec
ker muscular dystrophies were analysed blind by restriction fragment l
ength polymorphisms (RFLPs) and a new, non-radioactive direct test bas
ed on competitive polymerase-chain-reaction (PCR) amplification. All o
bligate carriers were correctly diagnosed by RFLPs and competitive PCR
, and 7 women with a 99% risk of being carriers were also diagnosed ca
rriers by competitive PCR. There were no false positives or false nega
tives. Only 1 PCR result was non-informative. Our test allows rapid, p
recise, and direct carrier diagnosis of women whose relatives have a k
nown deletion of the dystrophin gene.