Congenital
Adrenal Hyperplasia
21-hydroxylase deficiency (also known as congenital
adrenal hyperplasia) is an inherited disorder that affects
the adrenal glands. These glands are located on top
of the kidneys and produce a variety of hormones that
regulate many essential functions in the body. Two of
these hormones, cortisol and aldosterone, are produced
from cholesterol through the activity of an enzyme called
21-hydroxylase. Cortisol has numerous functions such
as maintaining blood sugar levels, protecting the body
from stress, and suppressing inflammation. Aldosterone,
sometimes called the salt-retaining hormone, acts on
the kidneys to regulate the levels of salt and water
in the body, which affects blood pressure. People with
21-hydroxylase deficiency have a shortage of the 21-hydroxylase
enzyme, which impairs the conversion of cholesterol
to cortisol and aldosterone. When the precursors of
cortisol and aldosterone build up in the adrenal glands,
they are converted to male sex hormones called androgens.
Androgens are normally responsible for the appearance
of secondary sex characteristics in males (virilization).
Elevated levels of androgens can affect the growth and
development of both males and females.
There are three types of 21-hydroxylase deficiency.
Two types are classic forms, known as the simple virilizing
and salt-loss types. Simple virilizing 21-hydroxylase
deficiency causes a buildup of potent androgens that
leads to the masculinization (development of male characteristics)
of external genitalia in females at birth. The development
of the internal reproductive organs (uterus and ovaries)
in these patients is normal. Salt-loss 21-hydroxylase
deficiency results from an almost complete loss of enzyme
activity. In these cases, so little aldosterone is produced
that the kidneys do not reabsorb sodium (a component
of salt). In the third type of 21-hydroxylase deficiency,
known as the nonclassic form, levels of functional 21-hydroxylase
enzyme are moderate. Both males and females with the
nonclassic type can display signs and symptoms of androgen
excess after birth.
The classic form of 21-hydroxylase deficiency appears
in 1 in 15,000 newborns. The prevalence of the nonclassic
form of 21-hydroxylase deficiency is estimated to be
1 in 100 individuals. The prevalence of both classic
and nonclassic forms may vary among different ethnic
populations.
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