Novel compound heterozygous mutations in the SRD5A2 gene from 46,XY infants with ambiguous external genitalia

Abstract

Dihydrotestosterone is crucial for normal development of external genitalia and prostate in the male embryo. Autosomal recessive mutations in the 5a-reductase type 2 (SRD5A2) gene disrupt the synthesis of dihydrotestosterone in the urogenital tract and give rise to genetic males with undervirilized external genitalia that may be femalelike or ambiguous. In this study, three unrelated 46,XY children (0.5, 3, and 8 years old) who presented severe undermasculinization at birth were examined for genetic abnormalities in the SRD5A2 gene. Coding sequence abnormalities were ascertained by exon-specific polymerase chain reaction (PCR), single-stranded conformational polymorphism (SSCP), and sequencing analysis. Functional properties of the mutant alleles were investigated by means of site-directed mutagenesis assays. DNA molecular studies showed that all three patients were compound heterozygotes for SRD5A2 mutations. Patient 1 had a point mutation 547G ? A in exon 3 (G183S) and a novel dinucleotidic mutation 634,635CC ? TG in exon 4 (P212X). This double change results in premature termination signal (TGA) at codon 212, which predicts the expression of a truncated 211-amino acid protein. Patient 2 was the carrier of mutations G115D in exon 3 and S210F in exon 4. Patient 3 had two substitution mutations in exon 1, including a novel G ? C transversion at nucleotide 169 (E57Q) and a G ? A transition at nucleotide 254 (G85D). In transitory transfection assays, the recombinant cDNAs harboring mutations E57Q and G85D showed residual 5a-reductase activity, whereas those with mutations G115D, S210F, and P212X were devoided of activity. In contrast, the G183S substitution affected the catalytic activity of the enzyme by decreasing its affinity for testosterone substrate. We describe six different mutations of the SRD5A2 gene detected in three children with genital ambiguity. These genotypes are consistent with the clinical phenotype of steroid 5a-reductase 2 deficiency. Our data suggest that the combined gene variants (E57Q/G85D, G115D/S210F, and G183S/P212X) result in subfunctional or nonfunctional enzymes, causing masculinization defects in these patients. This further underscores that exon 4 of SRD5A2 may be a site prone to inactivating mutations.

Phenotypic and molecular characteristics in eleven Chinese patients with 5α‐reductase Type 2 deficiency

“…Measurement of the ratios of 5α‐ to 5β‐reduced steroids in urine has been used to confirm the diagnosis, which otherwise requires diagnostic tests that are not widely available. Therefore, as a reliable approach to identify this disorder, DNA sequencing of the entire 5α‐reductase type 2 gene (SRD5A2) is necessary, particularly in prepubertal patients …”

Human Chorionic Gonadotropin Test: Old Uncertainties, New Perspectives, and Value in 46,XY Disorders of Sex Development

“…Basal T/DHT ratio showed high sensitivity in adults ( Table 5 ), providing that an adequate cut-off value is used. According to the data summarized in Data are collected from individual published values in patients with proven SRD5A2 mutations [Saenger et al, 1978;Odame et al, 1992;Hiort et al, 1996;Sinneker et al, 1996;Canto et al, 1997;Can et al, 1998;Nordenskjöld and Ivarsson, 1998;Ocal et al, 2002;Fernández-Ciancio et al, 2004;Bahceci et al, 2005;Hackel et al, 2005;Skordis et al, 2005;Kim et al, 2006;Baldinotti et al, 2008;Vilchis et al, 2008;Zhu et al, 2014;Bertelloni et al, 2016].…”

Practical approach to steroid 5alpha-reductase type 2 deficiency

“…The p.G203S mutation has been observed in a compound heterozygous Mexican patient (p.G115D/p.G203S) who was reared as a male and exhibited a more masculine phenotype [8]. The combined gene variants (E57Q/G85D, G115D/S210F, and G183S/P212X) result in subfunctional or nonfunctional enzymes, causing masculinization defects [42]. The G196S (homozygosity) produces a predominantly male phenotype, and in all of the affected children that have been reported, the phallus is so large that they are identified as males with hypospadias and raised as boys [32].…”