Characterization of 35 novel NR5A1/SF-1 variants identified in individuals with atypical sexual development: The SF1next study.

CONTEXT: Steroidogenic factor 1 (NR5A1/SF-1) is a nuclear receptor that regulates sex development, steroidogenesis and reproduction. Genetic variants in NR5A1/SF-1 are common among differences of sex development (DSD) and associate with a wide range of phenotypes, but their pathogenic mechanisms remain unclear. OBJECTIVE: Novel, likely disease-causing NR5A1/SF-1 variants from the SF1next cohort of individuals with DSD were characterized to elucidate their pathogenic effect. METHODS: Different in silico tools were used to predict the impact of novel NR5A1/SF-1 variants on protein function. An extensive literature review was conducted to compare and select the best functional studies for testing the pathogenic effect of the variants in a classic cell culture model. The missense NR5A1/SF-1 variants were tested on the promoter luciferase reporter vector -152CYP11A1_pGL3 in HEK293T cells and assessed for their cytoplasmic/nuclear localization by Western blot. RESULTS: Thirty-five novel NR5A1/SF-1 variants were identified in the SF1next cohort. Seventeen missense NR5A1/SF-1 variants were functionally tested. Transactivation assays showed reduced activity for 40% of the variants located in the DNA binding domain and variable activity for variants located elsewhere. Translocation assessment revealed three variants (3/17) with affected nuclear translocation. No clear genotype-phenotype, structure-function correlation was found. CONCLUSIONS: Genetic analyses and functional assays do not explain the observed wide phenotype of individuals with these novel NR5A1/SF-1 variants. In nine individuals, additional likely disease-causing variants in other genes were found, strengthening the hypothesis that the broad phenotype of DSD associated with NR5A1/SF-1 variants may be caused by an oligogenic mechanism.

Adrenal Abcg1 Controls Cholesterol Flux and Steroidogenesis.

Cholesterol is the precursor of all steroids, but how cholesterol flux is controlled in steroidogenic tissues is poorly understood. The cholesterol exporter ABCG1 is an essential component of the reverse cholesterol pathway and its global inactivation results in neutral lipid redistribution to tissue macrophages. The function of ABCG1 in steroidogenic tissues, however, has not been explored. To model this, we inactivated Abcg1 in the mouse adrenal cortex, which led to an adrenal-specific increase in transcripts involved in cholesterol uptake and de novo synthesis. Abcg1 inactivation did not affect adrenal cholesterol content, zonation, or serum lipid profile. Instead, we observed a moderate increase in corticosterone production that was not recapitulated by the inactivation of the functionally similar cholesterol exporter Abca1. Altogether, our data imply that Abcg1 controls cholesterol uptake and biosynthesis and regulates glucocorticoid production in the adrenal cortex, introducing the possibility that ABCG1 variants may account for physiological or subclinical variation in stress response.

Genetic reanalysis of patients with a difference of sex development carrying the NR5A1/SF-1 variant p.Gly146Ala has discovered other likely disease-causing variations.

NR5A1/SF-1 (Steroidogenic factor-1) variants may cause mild to severe differences of sex development (DSD) or may be found in healthy carriers. The NR5A1/SF-1 c.437G>C/p.Gly146Ala variant is common in individuals with a DSD and has been suggested to act as a susceptibility factor for adrenal disease or cryptorchidism. Since the allele frequency is high in the general population, and the functional testing of the p.Gly146Ala variant revealed inconclusive results, the disease-causing effect of this variant has been questioned. However, a role as a disease modifier is still possible given that oligogenic inheritance has been described in patients with NR5A1/SF-1 variants. Therefore, we performed next generation sequencing (NGS) in 13 DSD individuals harboring the NR5A1/SF-1 p.Gly146Ala variant to search for other DSD-causing variants and clarify the function of this variant for the phenotype of the carriers. Panel and whole-exome sequencing was performed, and data were analyzed with a filtering algorithm for detecting variants in NR5A1- and DSD-related genes. The phenotype of the studied individuals ranged from scrotal hypospadias and ambiguous genitalia in 46,XY DSD to opposite sex in both 46,XY and 46,XX. In nine subjects we identified either a clearly pathogenic DSD gene variant (e.g. in AR) or one to four potentially deleterious variants that likely explain the observed phenotype alone (e.g. in FGFR3, CHD7). Our study shows that most individuals carrying the NR5A1/SF-1 p.Gly146Ala variant, harbor at least one other deleterious gene variant which can explain the DSD phenotype. This finding confirms that the NR5A1/SF-1 p.Gly146Ala variant may not contribute to the pathogenesis of DSD and qualifies as a benign polymorphism. Thus, individuals, in whom the NR5A1/SF-1 p.Gly146Ala gene variant has been identified as the underlying genetic cause for their DSD in the past, should be re-evaluated with a NGS method to reveal the real genetic diagnosis.

Basics of androgen synthesis and action.

Androgens are essential sex steroid hormones for both sexes. Testosterone (T) is the predominant androgen in males, while in adult females, T concentrations are about 15-fold lower and androgen precursors are converted to estrogens. T is produced primarily in testicular Leydig cells in men, while in women precursors are biosynthesised in the adrenal cortex and ovaries and converted into T in the periphery. The biosynthesis of T occurs via a series of enzymatic reactions in steroidogenic organs. Notably, the more potent androgen, dihydrotestosterone, may be synthesized from T in the classic pathway, however, alternate metabolic pathways also exist. The classic action of androgens on target organs is mediated through the androgen receptor, which regulates nuclear receptor gene transcription. However, the androgen-androgen receptor complex may also interact directly with membrane proteins or signaling molecules to exert more rapid effects. This review summarizes the current knowledge of androgen biosynthesis, mechanisms of action and endocrine effects in human biology, and relates these effects to respective human congenital and acquired disorders.