SUN-149 Low level Mosaic LHX1 Gene Deletion Contributes to Mayer-Rokitansky-Küster-Hauser (MRKH) Syndrome

Abstract Disclosure: D. Kira: None. L.P. Chorich: None. Z.A. Hawkins: None. S. Brakta: None. H. Kim: None. J.A. Phillips: None. L.C. Layman: None. Introduction: MRKH syndrome is a rare severe Mullerian Duct (MD) anomaly where the uterus and upper 2/3 of the vagina fail to develop. Females with MRKH present with primary amenorrhea, but with normal ovaries, hypothalamic-pituitary-gonadal axis and secondary sex characteristics. There are 2 types of MRKH: isolated Mullerian aplasia (type1) or combined with additional congenital anomalies (type2). For most cases, the etiology of MRKH is still unknown. The genetics of MRKH is not well understood, but pathogenic variants in WNT4, HNF1B, and ZNHIT3 have been reported. LHX1 is a Lim domain transcription factor that has been extensively studied in animals. The Lhx1null mouse model is embryonic lethal, but conditional knockout models found it important in the urogenital system development. In humans, convincing evidence for LHX1 variants is lacking. Exome sequencing failed to reveal pathogenic variants in 134 patient samples, so we tested for gene deletions by genomic qPCR and RT-PCR, which suggested a possible heterozygous intragenic variant. Hypothesis: A low level mosaic pathogenic (P) / likely pathogenic (LP) variant in LHX1 could be associated with MRKH that otherwise would have been lethal. Methods: gDNA was extracted from peripheral blood samples from the 3 individuals with LHX1 variants and analyzed by colony PCR and Sanger sequencing to map the deletion, confirm the heterozygous allele and determine level of mosaicism. Results: We previously found that exon 4 was deleted by RT-PCR in these three (2.2%) unrelated MRKH patients, who had the same heterozygous 166bp frameshift deletion with a premature stop codon (c.676_841del;p.V226Ifs*120) in exon 4 predicted to impair the function of LHX1. This was not found in their unaffected family members. Mapping the variant showed a 1864bp deletion that spanned the whole length of intervening sequence 3, exon 4, and intervening sequence 4. Colony PCR results showed that 2/59 (3.4%), 4/65 (6.2%), and 1/95 (1%) colonies had the deletion in the 3 MRKH patients. Conclusion: Recently, it has become increasingly apparent that mosaicism may occur in human genetic diseases. Our lab has observed chromosomal mosaicism for structural variants in ∼3% of women with MRKH utilizing optical genome mapping (Brakta et al, 2023), and others have noted mosaicism in 2-3% of patients who underwent deep sequencing. Mosaicism can allow the presentation of a disease phenotype of a variant that would have otherwise been lethal in the non-mosaic state. Our next step will be to utilize targeted deep sequencing of about 70-100 genes already known to be implicated in the mice urogenital system and MD development. Studying the role of low level (10%) mosaicism is challenging since tissue remnants of underdeveloped MDs in MRKH patients are difficult to obtain. Presentation: Sunday, July 13, 2025