5-alpha reductase deficiency – causes, symptoms, diagnosis, treatment, pathology


5α- reductase deficiency is a genetic disorder
in which a protein called 5α reductase is defective or absent. 5α- reductase is an enzyme that converts
the male hormone testosterone to its more potent form, called dihydrotestosterone. One of the most important roles of dihydrotestosterone
is to help male external genitalia develop in a male fetus. Alright, so, normally, very early on in fetal
life, male and female internal sex organs and external genitalia are undifferentiated
and look identical. Within the first few months of development,
testes develop in the male fetus. The testes start producing testosterone which
is a male steroid hormone that belongs to a class of hormones called androgens. The testosterone gets released into the blood
and a tiny fraction of it gets converted to dihydrotestosterone by 5α- reductase, which
is mainly made in the skin of the genital area. Over time, dihydrotestosterone levels start
rising and it affects undifferentiated genital structures. Looking closely at these structures, at the
top there’s the genital tubercle, which is a small projection. Just below that, there’s the urethral groove,
which is the external opening of the urogenital sinus or the future urethra and bladder and
that’s surrounded by the urethral folds and the labioscrotal swellings. Now, once dihydrotestosterone reaches these
structures, it makes the genital tubercle elongate into the phallus which will eventually
be the penis. The elongating genital tubercle pulls up the
urethral folds which fuse in the midline, forming the spongy or penile urethra. The tips of the urethral folds remain unfused
and that forms the external urethral opening at the distal tip of the penis. The labioscrotal swellings also fuse proximally
to form the scrotum, which eventually houses the testes. In females, the gonads develop into ovaries,
which produce very low levels of androgens, so the genital tubercle remains small, forming
the clitoris and the urethral folds and labioscrotal swellings remain unfused or separate, surrounding
the opening of the vagina. This process is usually complete by month
four of fetal development. In 5α- reductase deficiency there’s a mutation
in the gene SRD5A2 and that reduces the amount of 5α- reductase enzyme that’s made. The condition is inherited in an autosomal
recessive but sex-limited pattern. This means that for the disease to appear,
both copies of the gene have to be mutated and the individual has to be genetically male,
with one X and one Y chromosome in each cell, since dihydrotestosterone has no role in the
development of genetically female individuals, with two X chromosomes in each cell. So the problem arises in a male fetus where
the testes produce testosterone, but it isn’t converted to dihydrotestosterone because the
5α- reductase enzyme is missing. As a result, while there are male internal
sex organs, the external genitalia follow more of a female path of development. Specifically, the phallus doesn’t fully
elongate, resembling something in between a clitoris and a penis, the scrotum often
remains split in two which is also called a bifid scrotum, and the urethral opening
remains on the underside of the penis, which is called hypospadias. The external genitalia doesn’t look clearly
male or female and is sometimes called ambiguous genitalia. When these individuals reach puberty, though,
there’s a huge increase in the levels of testosterone. Even though it can’t be converted to dihydrotestosterone,
there’s so much testosterone around that the phallus and scrotum grow larger and start
having more of a male appearance. In addition, the high levels of testosterone
will usually lead to deepening of the voice, muscle growth and development of facial and
body hair. Some individuals with 5α- reductase deficiency
adopt a male gender role, while others adopt a female gender role. Most individuals with 5α- reductase deficiency
also struggle with infertility. Diagnosis of 5α- reductase deficiency is
usually suspected in newborns with ambiguous genitalia. A karyotype can be used to visualize the sex
chromosomes X and Y and ensure that the individual is genetically male. Lab studies usually show a normal serum testosterone
level, low dihydrotestosterone levels, and therefore a high testosterone to dihydrotestosterone
ratio. Treatment of 5α- reductase deficiency focuses
on hormone replacement therapy. That means giving male or female sex hormones,
according to the gender role adopted by the individual. Surgical procedures can also be done to help
restore external genitalia to a non-ambiguous appearance. For those struggling with infertility, assisted
reproduction techniques are useful, too. All right, as a quick recap, 5α- reductase
deficiency results in a male fetus being unable convert testosterone to its more active form,
dihydrotestosterone. This leads to male internal organs and ambiguous
external genitalia. Both sex hormones and surgery can be done
to help align the external genitalia with the gender identity adopted by
the individual.

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