Genotype Identification of Complete Hydatidiform Moles without a Maternal Component: Attempts at a Novel 26-plex STR System.

Objective: Current autosomal short tandem repeat (STR) assays can analyze the zygotic composition by comparing the allelic genes at each locus of complete hydatidiform moles (CHM), with a maternal genotype serving as an essential reference for comparative analysis. However, their application in pathology represents a challenge because of deficiency or contamination of maternal-origin tissues. This study aimed to develop a novel STR genotyping method for identifying CHM genotypes without a maternal component.

Methods: Samples with the pathologic description of molar pregnancy were collected. Routine hematoxylin-eosin (HE) staining and p57 immunohistochemistry staining were conducted in accordance with standard guidelines. A novel 26-plex system was explored to classify CHM and diploid pregnancies. The system combined 22 STRs on chromosomes 21/18/13/X, 3 sex loci, and 1 quality control marker (TAF9L), enabling molecular diagnosis in the absence of maternal tissue. At last, traditional DNA typing based on villi and decidua (maternal component) of each case was used for result consistency analysis.

Results: CHM and nonmolar abortus could not be distinguished by the basic HE staining with no fetal evidence or other prominent features. DNA typing was successfully processed for all cases according to the novel 26-plex and traditional system. CHM (46XX) diagnosis required single A-STR/X-STR peaks and absent Y-chromosome markers, excluding chromosomal abnormalities via TAF9L analysis. When the villous tissue analysis revealed single peaks at X-STR/SRY loci, a 1:1 amelogenin ratio, and a 2:1 TAF9L peak ratio, these results overlapped with those of 46XY hydropic abortus or CHM. Notably, p57 immunohistochemical staining resolved the ambiguity. Consistency with traditional DNA genotyping confirmed system accuracy. This multiplex assay enhanced reliability in mole diagnosis, supporting clinical differentiation and genetic counseling.

Conclusion: This study presents a rapid and cost-effective assay for the genotypic identification of CHM without the need for a maternal component. The method combined the characteristics of STR loci distributed across different chromosomes and developed the clinic application of forensic biomarkers.