LEYDIG CELL HYPOPLASIA: A UNIQUE PARADOX IN THE DIAGNOSIS OF 46,XY DISORDERS OF SEX DEVELOPMENT

Objective: Disorders of sex development (DSD) are defined as conditions in which chromosomal sex is inconsistent with phenotypic sex, or in which the phenotype is not classifiable as either male or female. Mutations in genes present in X, Y or autosomal chromosomes can cause abnormalities of testis determination or 46,XY DSD. Leydig cell hypoplasia (LCH), also known as Leydig cell agenesis, is a rare autosomal recessive endocrine syndrome of 46,XY DSD. Our objective here is to present the case of a 27-year-old, phenotypic female who presented with primary amenorrhea and later found to have LCH. Methods: We used formatted history and clinical examination followed by necessary hormonal investigations. The diagnosis was confirmed by histopathology of resected testes and genetic mutation analysis. Results: The patient's physical examination was unremarkable except 2 ovoid lumps present in the inguinovulvar region. There were no müllerian structures on sonography. Estrogen and both basal and stimulated testosterone levels were low whereas luteinizing hormone and follicle-stimulating hormone were high. Her chromosomal sex was found to be 46,XY. The histopathology of the resected inguinal lumps showed atrophic testicular change lacking Leydig cells with relative preservation of Sertoli cells. Genetic mutation analysis failed to reveal any significant aberration in the LHCGR gene. At present she is on estrogen replacement therapy having undergone bilateral orchidectomy and vaginoplasty. Conclusion: LCH represents a unique example of diagnostic dilemma in gender identification. It requires a multidisciplinary approach for optimum outcome.

Protection Against XY Gonadal Sex Reversal by a Variant Region on Mouse Chromosome 13

XY C57BL/6J (B6) mice harboring a Mus musculus domesticus-type Y chromosome (YPOS), known as B6.YPOS mice, commonly undergo gonadal sex reversal and develop as phenotypic females. In a minority of cases, B6.YPOS males are identified and a proportion of these are fertile. This phenotypic variability on a congenic B6 background has puzzled geneticists for decades. Recently, a B6.YPOS colony was shown to carry a non-B6-derived region of chromosome 11 that protected against B6.YPOS sex reversal. Here. we show that a B6.YPOS colony bred and archived at the MRC Harwell Institute lacks the chromosome 11 modifier but instead harbors an ∼37 Mb region containing non-B6-derived segments on chromosome 13. This region, which we call Mod13, protects against B6.YPOS sex reversal in a proportion of heterozygous animals through its positive and negative effects on gene expression during primary sex determination. We discuss Mod13’s influence on the testis determination process and its possible origin in light of sequence similarities to that region in other mouse genomes. Our data reveal that the B6.YPOS sex reversal phenomenon is genetically complex and the explanation of observed phenotypic variability is likely dependent on the breeding history of any local colony.

Male mice lacking ADAMTS-16 are fertile but exhibit testes of reduced weight

Adamts16 encodes a disintegrin-like and metalloproteinase with thrombospondin motifs, 16, a member of a family of multi-domain, zinc-binding proteinases. ADAMTS-16 is implicated in a number of pathological conditions, including hypertension, cancer and osteoarthritis. A large number of observations, including a recent report of human ADAMTS16 variants in cases of 46,XY disorders/differences of sex development (DSD), also implicate this gene in human testis determination. We used CRISPR/Cas9 genome editing to generate a loss-of-function allele in the mouse in order to examine whether ADAMTS-16 functions in mouse testis determination or testicular function. Male mice lacking Adamts16 on the C57BL/6N background undergo normal testis determination in the fetal period. However, adult homozygotes have an average testis weight that is around 10% lower than age-matched controls. Cohorts of mutant males tested at 3-months and 6-months of age were fertile. We conclude that ADAMTS-16 is not required for testis determination or male fertility in mice. We discuss these phenotypic data and their significance for our understanding of ADAMTS-16 function.

ZNRF3 functions in mammalian sex determination by inhibiting canonical WNT signaling

Mammalian sex determination is controlled by the antagonistic interactions of two genetic pathways: The SRY-SOX9-FGF9 network promotes testis determination partly by opposing proovarian pathways, while RSPO1/WNT-β-catenin/FOXL2 signals control ovary development by inhibiting SRY-SOX9-FGF9. The molecular basis of this mutual antagonism is unclear. Here we show that ZNRF3, a WNT signaling antagonist and direct target of RSPO1-mediated inhibition, is required for sex determination in mice. XY mice lacking ZNRF3 exhibit complete or partial gonadal sex reversal, or related defects. These abnormalities are associated with ectopic WNT/β-catenin activity and reduced Sox9 expression during fetal sex determination. Using exome sequencing of individuals with 46,XY disorders of sex development, we identified three human ZNRF3 variants in very rare cases of XY female presentation. We tested two missense variants and show that these disrupt ZNRF3 activity in both human cell lines and zebrafish embryo assays. Our data identify a testis-determining function for ZNRF3 and indicate a mechanism of direct molecular interaction between two mutually antagonistic organogenetic pathways.