FGF9 variant in 46,XY DSD patient suggests a role for dimerization in sex determination

Abstract

46,XY gonadal dysgenesis (GD) is a Disorder/Difference of Sex Development (DSD) that can present with phenotypes ranging from ambiguous genitalia to complete male-to-female sex reversal. Around 50% of 46,XY DSD cases receive a molecular diagnosis. In mice, Fibroblast growth factor 9 (FGF9) is an important component of the male sex-determining pathway. Two FGF9 variants reported to date disrupt testis development in mice, but not in humans. Here, we describe a female patient with 46,XY GD harbouring the rare FGF9 variant (missense mutation), NM_002010.2: c.583G > A;p.(Asp195Asn) (D195N). By biochemical and cell-based approaches, the D195N variant disrupts FGF9 protein homodimerisation and FGF9-heparin-binding, and reduces both Sertoli cell proliferation and Wnt4 repression. XY Fgf9 D195N/D195N foetal mice show a transient disruption of testicular cord development, while XY Fgf9 D195N/À foetal mice show partial male-to-female gonadal sex reversal. In the general population, the D195N variant occurs at an allele frequency of 2.4 Â 10 À5 , suggesting an oligogenic basis for the patient's DSD. Exome analysis of the patient reveals several known and novel variants in genes expressed in human foetal Sertoli cells at the time of sex determination. Taken together, our results indicate that Brittany Croft and Anthony D. Bird contributed equally to this work.

Hormones and Signaling Pathways Involved in the Stimulation of Leydig Cell Steroidogenesis

“…Although Fgf9 knockout mice die at birth, analysis of embryos revealed partial or complete XY gonadal sex reversal [157]. A similar phenotype is observed in humans harboring an FGF9 variant (D195N) associated with 46 XY Difference of Sex Development (DSD) [158].…”

A role for TRPC3 in mammalian testis development

“…The TRPC3 mutation falls within the highly conserved TRP box (EWKFAR) which is implicated in channel gating ( Clapham, 2003 ; Fogel et al, 2015 ; Chen et al, 2021 ), and overexpression of the mutant TRPC3 protein led to significant cell death and increased nuclear localization of the calcium-responsive transcription factor NFAT ( Fogel et al, 2015 ). We previously identified the same TRPC3 R762H variant as one of only 24 candidate modifiers in a 46, XY DSD patient with an FGF9 variant (c.583G > A; p. Asp195Asn) ( Croft et al, 2023 ). To assess the pathogenicity of the TRPC3 variant, knock-in mice could be generated and be crossed with Fgf9 mutant mice to model the 46, XY DSD patient and assess the effects of both variants on testis development in mice.…”