Polymerase chain reaction detection of the Dde I polymorphism in the factor 9 gene for fragile X linkage analysis

We have used the polymerase chain reaction (PCR) to analyze the 50 base pair (bp) insertion/deletion polymorphism in the coagulation factor 9 gene. This procedure is particularly applicable for DNA marker studies in fragile X families. The polymorphism, which can also be detected in Dde I digestions, was detected by the amplification of fragments of 298 and 348 bp. The alleles were distinguished directly by agarose gel electrophoresis. PCR detection of this polymorphism is much simpler, more accurate, and quicker than conventional analysis.