Functional Validation of a Novel PBX1 Missense Variant in a 46,XY Girl

The pre-B-cell leukemia transcription factor encoded by PBX1 is expressed throughout human embryonic stages. Accumulating cases with differences of sex development (DSDs) have been reported harboring PBX1 variants, suggesting a yet elusive role of PBX1 in the gonadal differentiation and sexual development processes.

We report a syndromic case of 46,XY DSD presenting severely undervirilized genitalia and gonadal dysgenesis with mixed ovarian and testicular differentiation, where whole-exome sequencing analysis identified a novel missense variant c.710G>C (p.R237T) in the highly conserved nuclear localization sequence in the three-amino acid loop extension domain of PBX1.

Compared with wild-type (WT) PBX1, PBX1 p.R237T reduced protein stability and hampered nuclear translocation of PBX1 in the inducible Flp-In TREx HEK293 cells. Induction with tetracycline significantly decreased cell proliferation in both Flp-In HEK293 PBX1 WT and p.R237T cells compared to untransfected HEK293 cells, while adhesive ability was not different. RNA sequencing identified differentially expressed genes in DSD-related genes, including MAP3K4, EMX2, KISS1R, and HOXA13 in cells expressing PBX1 p.R237T when compared to cells expressing WT PBX1.

Altogether, our results demonstrated the deleterious functional consequences of the rare PBX1 p.R237T variant identified in a Taiwanese proband with 46,XY DSD.