Molecular screening of XY SRY-negative sex reversal cases in horses revealed anomalies in amelogenin testing

Abstract

Male-to-female sex reversal in horses is a developmental disorder in which phenotypic females have a male genetic constitution. Male-to-female sex reversal is the second most common genetic sex abnormality, after X chromosome monosomy. All male-to-female sex reversal cases studied to date have been found to be infertile. Therefore, a screening test is particularly useful in laboratories doing DNA genotyping in horses. Our laboratory has tested > 209,000 horses for parentage using a panel of microsatellite markers and the sex marker gene amelogenin (AMEL). Suspect XY sex reversal cases are reported females with a male profile by AMEL testing. After routine genotyping, 49 cases were detected and further tested using the sex-determining region Y (SRY) gene, confirming the XY SRY-negative genotype of suspect sex reversal cases. When some inconsistencies arose in the initial result, a molecular panel of X- and Y-linked markers was analyzed for these samples. Of the 49 cases, 33 were confirmed as XY SRY-negative. The remaining 16 cases were identified as false-positives as a result of anomalies of AMEL testing in horses.

Keywords: AMEL gene; SRY gene; XY sex reversal; amelogenin; horses.

Figure 1.

Electropherograms of X-linked markers (TKY38, UCDEQ502, Lex003, Lex026, TKY270, and AMELX) and Y-linked markers (ECAYH12, ECAYM2, ECAYA16, SRY, and AMELY): A. confirmed XY SRY-negative sex reversal case, showing amplification for all Y-linked markers, except SRY; B. false-positive XY sex reversal, showing amplification for only X-linked markers, except AMELY; C. false-positive XX SRY-positive sex reversal case, showing amplification for all Y-linked markers, except AMELY. In the images, AMEL is indicated by a circle.