Competitive assay to improve the specificity of detection of single-point mutations in alpha 1-antitrypsin deficiency.

Allele-specific oligonucleotides are used widely for the detection of single point mutations in genes. A modification of this assay based on competition has been developed for detection of the Z mutation of alpha 1-antitrypsin (alpha 1-AT). The normal alpha 1-AT allele is referred to as M, and the Z mutation arises from a single base substitution. Amplified DNA products corresponding to homozygous M, heterozygous MZ, and homozygous Z obtained by the polymerase chain reaction were incubated with a twofold molar excess of unlabeled oligonucleotide prior to hybridization with a radiolabeled oligonucleotide. Thus, initial incubation with unlabeled M-specific oligonucleotide was followed by hybridization with radiolabeled Z-specific oligonucleotide, and vice versa. This assay increased the specificity of single-point mutation detection three- to four-fold. Furthermore, specific hybridization was obtained at a lower temperature as a consequence of improving the signal-to-noise ratio.