Achondroplasia (ACH) is the most frequent form of short-limb dwarfism. Recently, 
the gene mutation responsible for ACH has been identified in the transmembrane 
domain of the fibroblast growth factor receptor 3 gene. The cause of ACH is a 
point mutation at nucleotide 1138 of the cDNA, resulting in the substitution of 
an arginine residue for a glycine. For the purpose of prenatal diagnosis of ACH, 
we have used the nested polymerase chain reaction to ensure the gene 
amplification. Although the normal allele has no restriction site around the 
causative sequence, we have devised an unique method to incorporate a 
restriction site of SplI into the normal allele only using modified primer sets. 
We report here the use of this polymerase chain reaction methodology which can 
ensure the gene amplification and omit the complicated steps of sequencing for 
prenatal diagnosis.