Deletion of amelogenin Y-locus: State of the art in gender determination

Accurate gender determination is widely used and it is crucial in many scientific disciplines, especially in profiling for DNA databasing, forensic casework (e.g., identifying the gender of biological material in stains of unknown origin), analysis of archeological specimens, preimplantation/prenatal diagnosis and post-natal diagnosis (e.g., X-linked diseases or children with ambiguous genitals). Today, molecular techniques, also based on length variation in the X–Y homologous amelogenin gene (AMELX and AMELY), are used for sex determination. In humans, the amelogenin gene is a single copy gene located on Xp22.1–Xp22.3 and Yp11.2 and it is sufficiently conserved, so the simultaneous detection of the X and Y alleles using polymerase chain reaction can lead to gender determination. There is a size difference of 6 bp between the X and the Y genes in the most widely used PCR primer set. The presence of two amplified products indicates a male genotype, while a single amplicon implies a female genotype. Several studies, published since 1998, have shown that normal males may be typed as females with this test because the amelogenin gender test may not always be concordant with true male gender: AMELY deletions may result in no amplification product and normal males being typed as female with the test (negative male). To date literature data have supported that the null allele is the result of a larger deletion on the short arm of the Y chromosome and that this occurs in different percentages in different population groups. Considering the consequences of the result obtained using only the amelogenin marker and the potential related interpretation difficulties, the gender misinterpretation may be troublesome in some cases, both in clinical practice and forensic caseworks. Different strategies have been proposed to solve this misinterpretation, such as the use of additional markers to resolve the possible occurrence of AMEY deletion. In this paper we propose a review of the incidence in failures of gender testing among different populations and the different strategies proposed in literature in case of doubt regarding the presence of deleted AME in the DNA profile.