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Virilization ormasculinization is the biological development of adult male characteristics in young males or females.[1] Most of the changes of virilization are produced byandrogens.
Virilization is a medicalterm commonly used in three medical andbiology of sex contexts: prenatal biologicalsexual differentiation, the postnatal changes of typical chromosomal male (46, XY)puberty, and excessive androgen effects in typical chromosomal females (46, XX). It is also the intended result ofandrogen replacement therapy in males withdelayed puberty andlow testosterone.
In the prenatal period, virilization refers to closure of theperineum, thinning and wrinkling (rugation) of thescrotum, growth of the penis, and closure of theurethral groove to the tip of thepenis. In this context,masculinization is synonymous withvirilization.
Prenatal virilization of XX fetuses and undervirilization of XY fetuses are common causes ofambiguous genitalia such as in conditions likeCongenital adrenal hyperplasia and5α-Reductase 2 deficiency.
For many years, it was widely believed that inmammals, the female is the "default" developmental pathway, and theSRY gene on theY chromosome is responsible for suppressing the development of female characteristics and stimulating males characteristics. In this scenario, anembryo would passively develop female sexual characteristics without intervention by the SRY gene. However, in the early 2000s, other genes, such asWNT4 andRSPO1, were discovered that perform the opposite function – i.e., genes which suppress masculinization and stimulate feminization.[2]
Two processes:defeminization, and masculinization, are involved in producingmale typical morphology and behavior.
Prenatal virilization of a genetically female fetus can occur when an excessive amount of androgen is produced by the fetaladrenal glands or is present in maternal blood, resulting in virilization of the female genitalia such as anenlarged clitoris.
It can also be associated withprogestin-induced virilisation.
Undervirilization can occur if a genetic male cannot produce enough androgen or the body tissues cannot respond to it. Extreme undervirilization occurs when no significant androgen hormones can be produced or the body is completely insensitive to androgens, in which case a female phenotype will develop. Partial undervirilization produces ambiguous genitalia part-way between male and female. Examples of undervirilization in fetuses with a 46,XY karyotype areandrogen insensitivity syndrome and5 alpha reductase deficiency.
In common as well as medical usage, virilization often refers to the process of normal malepuberty. These effects include growth of the penis and the testes, accelerated growth,development of pubic hair, and other androgenic hair of face, torso, and limbs,deepening of the voice, increased musculature, thickening of the jaw, prominence of the neck cartilage, and broadening of the shoulders.
Virilization can occur in childhood in both males and females due to excessive amounts of androgens. Typical effects of virilization in children arepubic hair, accelerated growth and bone maturation, increasedmuscle strength,acne, and adult body odor. In males, virilization may signalprecocious puberty, whilecongenital adrenal hyperplasia and androgen producing tumors (usually) of thegonads or adrenals are occasional causes in both sexes.[3]
Virilization in females can manifest asclitoral enlargement, increased muscle strength, acne,hirsutism, frontal hair thinning, deepening of the voice,menstrual disruption due toanovulation, and a strengthened libido.[4] Some of the possible causes of virilization in females are:
Transgender people who were medically assigned female at birth sometimes elect to takehormone replacement therapy. This process causes virilization by inducing many of the effects of a typically male puberty. Many of these effects are permanent, but some effects can be reversed if the transgender individual stops or pauses their medical treatment.
Demasculinization refers to the reversal of virilization. Some but not all aspects of virilization are reversible. Demasculinization occurs naturally withandropause, pathologically withhypogonadism, and artificially or medically withantiandrogens,estrogens, andorchiectomy. It is desired by manytransgender women who have undergone the changes of pubertal masculinization. Some virilized traits remain though (such as body hair, a hardjawline and an enlargedlarynx), due to the fashion in which virilization affects a body's physiology.
