Genome sequencing and transcriptome profiling in twins discordant for Mayer-Rokitansky-Küster-Hauser syndrome

Objective Mayer-Rokitansky-Küster-Hauser syndrome (MRKH) is a rare congenital disease manifesting with aplasia or severe hypoplasia of uterine structures. Even though extensive studies have been performed, for the majority of cases the etiology remains unclear. In this study, we sought to identify genetic causes in discordant monozygotic (MZ) twins using genome sequencing of blood of both twins as well as uterine tissue of the affected twin. In addition, we profiled the endometrial transcriptome of affected twins to compare perturbations with those of sporadic MRKH cases. Results First, analyzing the data under the assumption that a variant solely identified in the affected twin or affected tissue could cause the phenotype, we identified a mosaic variant in ACTR3B with a high allele frequency in affected tissue, a low allele frequency in blood of the affected twin and almost absent in the blood of the unaffected twin. Since ACTR3B has not been reported for genitourinary anomalies before, clinical relevance of the variant needs to be clarified. Second, examining the data for candidate genes previously implied in MRKH, we detected a pathogenic variant in GREB1L in one twin pair and their unaffected mother showing a reduced phenotypic penetrance. Furthermore, two variants of unknown clinical significance in PAX8 and WNT9B were identified. Analysis for copy number and structural variants revealed no discordant variants in the twins or variants in candidate genes or regions. Third, we conducted transcriptome analysis of affected tissue and observed widespread perturbations largely similar to those in sporadic MRKH cases. These shared transcriptional changes were enriched for terms associated with estrogen and its receptors pointing at a key role of estrogen in MRKH pathology. Conclusion Our study on genome sequencing of blood and uterine tissue of discordant twins is the most extensive study performed on twins discordant for MRKH so far. Nevertheless, no clear pathogenic differences in the twins or between blood and tissue samples were detected. This points towards a more complex etiology of MRKH less dependent on genetic differences and more determined by epigenetic changes or environmental factors. Our transcriptome data showed a clear overlap with gene expression data of sporadic MRKH cases, indicating that the etiology for MRKH in discordant twins and sporadic cases is largely similar.