5-Alpha Reductase Deficiency - An Overview

Introduction:

Ambiguous genitalia is an uncommon condition characterized by external genitalia that are not distinctly male or female. This condition affects about one in 4,500 newborns. One potential cause is 5-alpha reductase deficiency. Even with modern technological advancements, detection rates before birth are limited to 20 to 40 percent of cases. This condition is also referred to as steroid 5-alpha reductase deficiency or pseudovaginal perineoscrotal hypospadias, which presents a male genotype, although the physical traits may vary individually. Though the exact prevalence of this rare condition is not well-documented, it appears to be more frequent in countries like Egypt, Turkey, the Dominican Republic, southern Lebanon, and Papua New Guinea. This article explores the causes, inheritance patterns, physical characteristics, diagnostic methods, and management of the condition.

What Is 5 Alpha Reductase Deficiency?

5-alpha reductase deficiency is a hereditary condition found in those with 46, XY chromosomes, typically indicating a male genetic identity. It interferes with sexual development because it prevents the conversion of testosterone to dihydrotestosterone (DHT), a vital hormone for the development of male sexual characteristics. The deficiency of this hormone can obstruct the development of external sex organs during fetal growth. Individuals with this condition often face varied gender assignments: some may be labeled female due to the appearance of the external female genitalia, while others might be assigned male if they have a small penis and a urethral opening located on the underside of the penis, a condition known as hypospadias. As puberty progresses, those affected by this condition see an elevation in male sex hormones, resulting in the emergence of male traits like a deepened voice, pubic hair, greater muscle mass, and a notable growth spurt. The scrotum and penis also expand, but fertility is generally compromised.

What Is the Cause of 5 Alpha Reductase Deficiency?

Mutations in the SRD5A2 (steroid 5 alpha-reductase 2) gene can cause 5-alpha reductase deficiency. This gene, found on chromosome 2, provides the instructions for creating the enzyme steroid 5-alpha reductase 2. This enzyme is key for converting testosterone into dihydrotestosterone (DHT), an androgen essential for the development of male sexual characteristics. Testosterone is vital before birth for the development of internal male reproductive structures such as the epididymis, vas deferens, and seminal vesicles. Meanwhile, dihydrotestosterone (DHT) is responsible for the growth of the prostate gland, penis, and scrotum. Both hormones are also important for the emergence of secondary sexual traits during puberty.

Studies have uncovered around 50 mutations within the SRD5A2 gene. These genetic changes modify the amino acid sequence of the steroid 5-alpha reductase 2 enzyme. Some of these mutations render the enzyme entirely inactive, whereas others diminish its activity to a certain extent. The occurrence of mutations in the SRD5A2 gene results in the body’s inability to transform testosterone into dihydrotestosterone (DHT). Without sufficient DHT, the development of external genitalia is disrupted. Hence, individuals with this condition, though genetically male, may have external genitalia that appears female, featuring a small penis and a urethral opening situated beneath the penis.

What Is Most Notable About Individuals With 5-Alpha Reductase Deficiency Disorder?

Genetically male individuals with this condition may present with diverse physical traits. At birth, their genitalia might resemble the labia majora, the external folds of the female vulva, because the labioscrotal folds do not properly fuse. Additionally, the phallus may appear more similar to a clitoris than to a penis. Internally, individuals with this condition possess male reproductive structures, including the epididymis, seminal vesicles, ejaculatory duct, and vas deferens. The testes are typically located in the inguinal sac, though they may occasionally be found in the abdomen. These individuals are usually raised as females, but during puberty, the phallus may enlarge, the testes may descend, and secondary sexual characteristics may develop.

How Is 5 Alpha Reductase Deficiency Diagnosed?

The diagnostic process encompasses gene analysis as well as biochemical testing.

• Gene Analysis: This method facilitates the analysis of an individual's genetic material. Mutations in the SRD5A2 gene are commonly observed, with the severity of the condition depending on how much function is lost in the SRD5A2 enzyme. The enzyme may be fully inactive in some cases, while in others, it may retain a small degree of activity.

• Biochemical Assay: The tests involve measuring the testosterone-to-DHT ratio following stimulation with human chorionic gonadotropin (hCG, a hormone). While the ratio usually increases in those with this disorder, there are instances where it does not, which can pose challenges for diagnosis.

How Is 5 Alpha Reductase Deficiency Inherited?

This condition is inherited in an autosomal recessive fashion, meaning that an individual inherits one defective gene from each parent. Parents typically carry one mutated gene each and do not display symptoms, hence they are called carriers. Genetically female individuals carrying both mutated copies of the SRD5A2 gene typically show no symptoms, and their sexual development is usually unaffected. However, it has been observed that they may encounter a delay in the start of menstruation.

What Is the Treatment of 5 Alpha Reductase Deficiency?

The approach to managing 5 alpha reductase deficiency depends on a variety of factors:

• In cases where the external male genitalia are affected, the child is usually brought up as female. This involves removing the testes and possibly performing corrective surgery. Should the child choose a female identity, reconstruction of the external genitalia to create a vaginal opening is considered, with vaginoplasty potentially being an option in their teenage years.

• If the child is brought up as a male, options for corrective surgery include urethral reconstruction and the correction of hypospadias.

The surgeries are usually carried out during the child’s first or second year. Parents are legally empowered to decide on both the treatment options and the child’s gender.

How Do 5 Alpha Reductase Deficiency and Androgen Insensitivity Differ?

While both 5 alpha reductase deficiency and androgen insensitivity syndrome involve genetically male individuals (XY) and have ambiguous genitalia, they differ in key aspects:

• Androgen insensitivity syndrome occurs when the body does not react to androgens, hormones essential for male sexual development. On the other hand, 5 alpha reductase deficiency involves a failure to convert testosterone into dihydrotestosterone (DHT), disrupting the development of male external sex organs in both cases.

• The AR (androgen receptor) gene on the X chromosome is mutated in androgen insensitivity syndrome, while 5 alpha reductase deficiency is due to mutations in the SRD5A2 gene.

• Androgen insensitivity syndrome is transmitted via an X-linked recessive trait, whereas 5 alpha reductase deficiency is inherited in an autosomal recessive manner.

Conclusion:

The prognosis for individuals with 5-alpha reductase deficiency is generally good, with no evidence of prostate cancer. Although most males with this condition are infertile, intrauterine insemination can help them achieve parenthood. As the child with this condition develops, involving a mental health nurse for counseling is important, as some children may experience conflicting emotions about their gender assignment.