Amplification Failure of the Amelogenin X Gene Caused by a Rare Mutation in the Primer-Binding Region

The study of gender markers is essential in forensic genetic analysis. Mutations in the X or Y homologs of the amelogenin gene can be misleading, resulting in serious mistakes in forensic genetic analysis. We recently discovered two male cases of the X homolog of the amelogenin (AMELX) allelic dropout while analyzing short tandem repeat genotypes obtained from crime scene evidence. Subsequently, we evaluated the molecular characteristics of AMELX allelic dropout in this study. We used two previously reported amelogenin primers to verify a half level of amelogenin gene amplification intensity in the two male cases, which we confirmed was caused by AMELX allelic dropout. We then characterized the point mutation using Sanger sequencing and designed mutation-specific primers that could overcome AMELX allelic dropout. Short tandem repeat genotyping analysis confirmed that the AMELX allelic dropout was recovered by the mutation-specific primer designed specifically for this case. The sequencing of the AMELX allele revealed a single-point variant from A→G at base position 7 downstream from the 3' end in the amelogenin forward primer-binding region. This point mutation was identically found in two different male cases, resulting in AMELX allelic dropout. To our knowledge, these mutations and the X homolog amplification failure of amelogenin have not been reported in the Korean population. Our study provides a reliable approach to AMELX allelic dropout due to rare case mutations and could enable the better interpretation of gender markers for forensic samples.