Molecular genotyping of hydatidiform moles: analytic validation of a multiplex short tandem repeat assay

Distinction of hydatidiform moles from non-molar (NM) specimens, as well as their subclassification as complete (CHM) versus partial hydatidiform moles (PHM), is important for clinical management and accurate risk assessment for persistent gestational trophoblastic disease. Because diagnosis of hydatidiform moles based solely on morphology suffers from poor interobserver reproducibility, a variety of ancillary techniques have been developed to improve diagnosis. Immunohistochemical assessment of the paternally imprinted, maternally expressed p57 gene can identify CHMs (androgenetic diploidy) by their lack of p57 expression, but cannot distinguish PHMs (diandric monogynic triploidy) from NMs (biparental diploidy). Short tandem repeat genotyping can identify the parental source of polymorphic alleles and thus discern androgenetic diploidy, diandric triploidy, and biparental diploidy, which allows for specific diagnosis of CHMs, PHMs, and NMs, respectively. In this study, a retrospectively collected set of morphologically typical CHMs (n = 8), PHMs (n = 10), and NMs (n = 12) was subjected to an analytic validation study of both short tandem repeat genotyping and p57 immunohistochemistry. Several technical and biological problems resulted in data that were difficult to interpret. To avoid these pitfalls, we have developed an algorithm with quantitative guidelines for the interpretation of short tandem repeat genotyping data.