Intersexuality is the condition where people are born with reproductive or sexual anatomy that does not fit the typical definitions of female or male. It occurs when there is discordance between chromosomal, gonadal, internal genital or phenotypic sex.
Some intersex traits are not visible at birth, only later. Others will not become aware that they are intersex unless they receive genetic testing, because their phenotype is either completely female or completely male.
There are about 60 – 70 intersex conditions.
Congenital adrenal hyperplasia
CAH is the most common cause of intersexuality in XX (genetically female) people, although it can occur in both sexes. This condition is characterised by enzyme deficiencies in the adrenocortical hormone synthesis. The most commonly affected hormone is 21-hydroxylase.
Females with the classic (21-hydroxylase deficiency) form of CAH have ambiguous genitalia, external genitalia that don’t look clearly male or female. They have enlarged clitorises or labia majora which resemble a scrotum. However, their internal reproductive organs develop normally.
People with CAH develop their secondary sexual characteristics earlier than normal, which may prevent further growth later and cause short stature in adulthood.
Klinefelter is characterised by 47XXY, the inheritance of an extra X chromosome from their father or mother. It affects 1:500 – 1:1000 male births.
The testes and penis are small, about half the normal size. Their ejaculate does not contain sperm. They may develop female secondary sexual characteristics, like little body hair, breast development, narrow shoulders, wide hips.
Androgen insensitivity syndrome (Morris syndrome)
AIS is the most common cause of intersexuality in XY (genetically male) people. It’s an X-linked recessive inherited condition which occurs due to a genetic defect in the androgen receptor, a gene on the X chromosome. This decreases the body’s response to androgens.
The defect may be partial, in which there is some response to androgens, or complete, in which there is no response. In the complete form, affected persons have female sexual characteristics, including external genitalia and physique. They don’t have uterus, but they do have cryptorchid testes. This makes them infertile.
In the partial form, the affected person can be anywhere on the spectrum from normal female sex characteristics to normal male sex characteristics to a mix between the two.
The cryptorchid testes are usually in the pelvis or abdomen and must be removed before the age of 18 – 20 to prevent cancer development.
5-alpha-reductase deficiency is characterised by a deficiency in the enzyme 5-alpha-reductase, which converts testosterone into dihydrotestosterone (DHT). This occurs in genetic males (46XY).
They have normal testes, but without DHT the male external genitalia don’t develop, causing female external genitalia to be present at birth. Patients usually grow up as females, but they may present in the school-age because the parents feel like the behaviour is more like that of a male.
Testosterone, not DHT is needed for development of male secondary sex characteristics in puberty, so at puberty these persons experience deepening of the voice, increased muscle mass, and growth of their external genital organs.
If a pregnant woman is exposed to high levels of androgens or androgenic progestins during pregnancy, a genetically female foetus may develop into an intersex individual. Their external genital organs at birth may be anything from “female with large clitoris” to “male with no testes”.
However, after birth the development continues normally. Surgical correction may be necessary but is relatively simple.
Gonadal dysgenesis is a group of disorders characterised by underdevelopment of the gonads during embryogenesis. They include:
- Turner syndrome
- Swyer syndrome (XY gonadal dysgenesis)
- XX gonadal dysgenesis
- True gonadal intersexuality
These conditions cause the formation of streak gonads, which are underdeveloped gonads, instead of testes or ovaries. Like in AIS, these abnormal gonads have a high risk for cancer and must be surgically removed.
Turner syndrome is characterised by the karyotype 45XO. It occurs when the whole or part of the X chromosome is lost before or soon after the time of conception. These patients have female phenotype, but because of their non-functioning ovaries they have minimal oestrogen production, causing delayed puberty and primary amenorrhoea.
Symptoms of Turner syndrome include:
- Short stature
- Short and webbed neck
- Low-set ears
- Low hairline
Hormone replacement therapy with oestrogen and growth hormone allows them to undergo puberty.
Swyer syndrome (XY gonadal dysgenesis)
People with Swyer syndrome are genetically male (46XY), however they have mutations in genes involved in male sexual development, most notably the SRY gene. This causes the development of the testes to be abnormal, which causes underproduction of testosterone and anti-Müllerian hormone.
The result is that these persons have a female external phenotype, including uterus and fallopian tubes.
Up until puberty, affected people develop normally as females. However, in puberty they will experience primary amenorrhoea, enlarged clitoris, and absence of breast enlargement. If they receive hormone replacement therapy, they will experience normal puberty and develop normal female secondary sex characteristics.
True gonadal intersexuality (“True hermaphroditism”)
In true gonadal intersexuality both ovarian and testicular tissue is present, sometimes in the same gonad, in which case it’s called an ovotestis. The person may also have one ovary and one testis.
Both the ovarian and testicular tissue aren’t functional, only one of them are. Depending on the levels of testosterone produced, the external genital may be female, male, or ambiguous.
B4. Functional diagnostics of the ovarian capacity, cycle diagnostic
B6. Physiology of puberty and menarche