Pediatric Differences in Sex Development

Early in fetal development, the tissue that will become the gonads (ovaries or testes) is identical and has the potential to become either ovaries or testes, depending on the genetics of the fetus. Humans have 46 chromosomes in each cell of their body, or 23 pairs. The 23rd pair is important for sex determination; females usually have two X chromosomes, while males usually have one X and one Y chromosome.

There is a gene located on the short arm (top half) of the Y chromosome, called SRY, which, if present, will cause the gonad to become testes (indicating a male) around the sixth week of fetal life. At the same time, the tissue that would have become the female reproductive organs (uterus and fallopian tubes) will disappear. As the testes produce testosterone (male hormone), the phallus (penis), scrotum and urethra form. Later, during the seventh to eighth month of the pregnancy, the testes will descend into the scrotum.

In the absence of the SRY gene, the gonad will become an ovary (indicating a female). Likewise, the female reproductive tract will continue to develop, forming the uterus and fallopian tubes. At the same time, the tissue that would have become the male reproductive organs (epididymis and vas deferens) occurs.

Changes in a number of genetic or hormonal factors can affect this process, leading to ambiguous genitalia. Ambiguous genitalia, as the word implies, may make determining the child's gender more difficult. More recently, the term Differences (or Disorders) of Sex Development (DSD) has been used to describe conditions in which the child’s genetics, hormones, internal organs or external genitalia are atypical.

It is important to know:

• These conditions are not as rare as most think and affect about 1 in 100 newborns.
• There is a wide variety of conditions which can cause ambiguous genitalia; healthcare providers can evaluate a child's condition to determine the best course of care.
• Children with DSD can sometimes have other congenital problems, but in general these children are healthy.
• One of the more common conditions known as congenital adrenal hyperplasia needs to be diagnosed and treated soon after birth to avoid serious illness in the baby.

Many genetic and environmental factors can affect the developing baby and lead to atypical genitalia. Ambiguous genitalia may make it harder to determine a baby’s gender. But very few newborns with this condition have genitals that are so ambiguous that the healthcare provider can’t figure out the gender at birth.

These are far more common at birth:

• A girl baby with too much of the male hormones (virilization) who seems to have a small penis
• A boy baby with an abnormally small penis that looks like a female clitoris. This is either because the baby did not respond to male hormones or the baby did not make male hormones.

Children who are born with ambiguous genitalia may fall into one of the following groups:

Sex chromosome DSD 

• Chromosomes can be a mixture of 45 X, 46 XX, 46 XY and 46 XXY
• Some people with sex chromosome DSD can have both ovarian and testicular tissue as well as both male and female internal organs

46 XY DSD

This entails cases where the chromosomes are 46 XY but the testes did not develop (gonadal dysgenesis), the hormones are not produced or the body does not respond or only partially responds to the hormones. These include:

• Complete androgen insensitivity syndrome:
  • 46, XY karyotype
  • Normal female external genitalia
  • This is called androgen insensitivity syndrome because the body does not respond to androgens (testosterone). Androgen insensitivity syndrome is inherited by a defect in the androgen receptor gene on the X chromosome and the inheritance is therefore described as X-linked recessive. Mothers who carry the gene have a 50/50 chance to have a 46 XY daughter with androgen insensitivity syndrome, while 46 XX daughters (of mothers who carry the gene) have a 50/50 chance to be carriers of the gene and thus pass it on to their children
• Partial androgen insensitivity:
  • 46 XY karyotype
  • Can have female external anatomy, male external anatomy or have features of both
  • People with partial androgen insensitivity only respond in part to androgens (testosterone)
• 5-alpha-reductase deficiency:
  • 46, XY karyotype
  • Genital ambiguity
  • The enzyme 5-alpha reductase is deficient; therefore, it cannot carry out its task of converting testosterone into dihydrotestosterone (DHT) which is necessary for complete masculinization of a male fetus. A 5-alpha-reductase deficiency is inherited by an autosomal recessive gene, which means that each parent carries one copy of the gene and transmits it to the child. With each pregnancy, carrier parents have a one in eight (or 12.5%) chance to have an affected child since only 46 XY infants are affected

46 XX DSD

• Happens when babies are exposed to excess male hormone due to a problem in their adrenal gland because they have the SRY gene and thus developed testes or due to external exposure to male hormones while they were developing in their mother’s uterus. The most common cause of 46 XX DSD is due to congenital adrenal hyperplasia (CAH).
  • About congenital adrenal hyperplasia (CAH):
    • Caused by a defect in an enzyme (21-hydroxylase) in the steroid hormone synthesis pathway in the adrenal gland
    • Most common cause of ambiguous genitalia in newborns
    • Causes females to be masculinized due to a deficiency of the enzyme 21-hydroxylase
    • Present in about one in 15,000 newborns
    • Inherited by an autosomal recessive gene. Autosomal recessive means that each parent carries one copy of the gene, and transmits the gene at the same time to the child.
    • With each pregnancy, carrier parents have a one in four (or 25%) chance of having an affected child. Affected females have ambiguous genitalia but affected males do not.
    • In some cases, the mother of a child with CAH can be given medications during pregnancy to lessen the effects of the enzyme deficiency if the fetus is female; but this still remains experimental.
    • Another type of CAH called salt-losing is very serious and often lethal due to changes in the blood levels of sodium and potassium in the newborn. Treatment is available and if diagnosed early, lethal side effects are avoided. Males and females are equally affected. There are other rarer enzyme problems which can result in CAH in either males or females.

There are a number of other syndromes in which ambiguous genitalia is one feature (characteristic) of the disorder in addition to other features.

When a child's genitalia appear ambiguous at birth, your child's physician will conduct both a medical history and a physical examination of your child's external genitalia. The medical history will include the mother's health during pregnancy and a family history of any neonatal deaths or genital abnormalities. Then diagnostic procedures are performed which may include a newborn screening test for CAH, hormonal studies and an ultrasound, and genetic/chromosomal studies.