5-α-Reductase type 2 deficiency: is there a genotype-phenotype correlation? A review

5-α-Reductase type 2 enzyme catalyzes the conversion of testosterone into dihydrotestosterone, a potent androgen responsible for male sexual development during the fetal period and later during puberty. Its deficiency causes an autosomal recessive disorder of sex development characterized by a wide range of under-virilization of external genitalia in patients with a 46,XY karyotype. Mutations in the SRD5A2 gene cause 5-α-Reductase deficiency; although it is an infrequent disorder, it has been reported worldwide, with mutational heterogeneity. Furthermore, it has been proposed that there is no genotype-phenotype correlation, even in patients carrying the same mutation. The aim of this review was to perform an extensive search in various databases and to select those articles with a comprehensive genotype and phenotype description of the patients, classifying their phenotypes using the external masculinization score (EMS). Thus, it was possible to objectively compare the eventual genotype-phenotype correlation between them. The analysis showed that for most of the studied mutations no correlation can be established, although the specific location of the mutation in the protein has an effect on the severity of the phenotype. Nevertheless, even in patients carrying the same homozygous mutation, a variable phenotype was observed, suggesting that additional genetic factors might be influencing it. Due to the clinical variability of the disorder, an accurate diagnosis and adequate medical management might be difficult to carry out, as is highlighted in the review.