CAH stands for congenital adrenal hyperplasia, a group of inherited conditions where the adrenal glands can’t produce certain hormones correctly. It affects roughly 1 in 9,500 births worldwide for the classic form, while a milder version occurs in about 1 in 1,000 births. The core problem is a genetic enzyme deficiency that disrupts hormone production, leading to too little cortisol and often an overproduction of androgens (sex hormones).
How CAH Affects the Adrenal Glands
Your adrenal glands sit on top of your kidneys and produce three key types of hormones from cholesterol: cortisol (which regulates metabolism and your immune response), aldosterone (which controls blood pressure and sodium balance), and androgens (sex hormones that drive secondary sex characteristics like body hair and voice changes).
In CAH, a faulty enzyme blocks part of this production line. When cortisol levels drop, the pituitary gland in your brain responds by sending more signaling hormones to the adrenals, essentially telling them to work harder. This extra stimulation causes the adrenal glands to enlarge, which is the “hyperplasia” in the name. But because the enzyme blockage is still there, the raw materials that should become cortisol get rerouted into androgen production instead. The result is too little cortisol, sometimes too little aldosterone, and a surplus of male sex hormones.
The Genetic Cause
CAH is an autosomal recessive condition, meaning a child must inherit a defective gene copy from both parents to develop it. About 95% of cases involve mutations in a gene called CYP21A2, which provides instructions for the enzyme 21-hydroxylase. Without enough of this enzyme, the adrenal glands can’t convert hormone precursors into cortisol and aldosterone efficiently. Over half of affected individuals carry two different mutations (one from each parent), while others have the same mutation on both gene copies.
Classic vs. Nonclassic CAH
CAH comes in two broad categories that differ significantly in severity and timing.
Classic CAH
Classic CAH is the more serious form, typically detected at birth or in infancy. It involves a severe cortisol deficiency and comes in two subtypes. Salt-wasting CAH, the most dangerous, also involves very low aldosterone. Without enough aldosterone, the body loses sodium through urine at a dangerous rate. In newborns, this can cause dehydration, vomiting, poor feeding, dangerously low blood pressure, and a life-threatening emergency called adrenal crisis within days or weeks of birth.
Simple virilizing CAH is the moderate form of classic CAH. Aldosterone production is reduced but not as severely, so the sodium-loss symptoms are less dramatic. Both subtypes cause excess androgens, which can lead to visibly atypical genitalia in female newborns (though internal reproductive organs develop normally) and signs of early puberty in young children of either sex, sometimes as early as age 2 or 3.
Nonclassic CAH
Nonclassic CAH is far milder and much more common. It often goes undiagnosed until later in childhood or adulthood because the enzyme still works partially. Symptoms tend to surface during adolescence or adulthood, particularly in women. In a large multicenter study, the most frequent symptoms among women with nonclassic CAH were excess facial and body hair (59%), irregular periods (54%), and acne (33%). Some women experience difficulty getting pregnant or hair thinning. Men with nonclassic CAH are rarely diagnosed because the extra androgens cause fewer noticeable problems in males.
How CAH Is Diagnosed
Most classic CAH is caught through newborn screening, which is standard in many countries. The screening measures blood levels of 17-hydroxyprogesterone (17-OHP), a hormone precursor that builds up when 21-hydroxylase isn’t working. In healthy full-term newborns, 17-OHP levels fall below 630 ng/dL and gradually drop to under 110 ng/dL in boys and under 100 ng/dL in girls by about six months of age. Levels well above these thresholds raise suspicion for CAH. Premature or sick infants can have temporarily elevated levels up to 1,000 ng/dL, which can complicate screening.
Nonclassic CAH is typically diagnosed later in life, often after a woman seeks help for irregular periods, excess hair growth, or fertility problems. A blood test measuring 17-OHP, sometimes combined with a stimulation test, confirms the diagnosis. Genetic testing for CYP21A2 mutations can provide definitive answers and help with family planning.
Treatment and Daily Management
The goal of treatment is straightforward: replace the hormones the body can’t make and bring androgen levels back to a normal range. Children with classic CAH typically take hydrocortisone to replace cortisol. Adults may use hydrocortisone or longer-acting alternatives like prednisone or dexamethasone. Those with salt-wasting CAH also take fludrocortisone to replace aldosterone and maintain sodium balance.
Treatment is lifelong for classic CAH. People with nonclassic CAH who have bothersome symptoms take lower doses of the same cortisol-replacing medications. Some women with nonclassic CAH choose not to treat the condition if their symptoms are mild.
One of the trickiest aspects of managing CAH is balancing hormone replacement. Too little medication leaves androgens elevated. Too much steroid medication can suppress growth in children and cause weight gain or bone thinning over time. Finding the right dose requires regular monitoring and adjustments, especially during childhood growth spurts and puberty.
Long-Term Effects on Growth and Fertility
Excess androgens in childhood accelerate bone development, which can cause rapid early growth followed by earlier-than-normal fusion of growth plates. The net effect is often shorter adult height. In one study of 30 men with classic CAH, average adult height was 164 cm (about 5’5″), significantly below the average for American men and shorter than expected based on their parents’ heights. Starting treatment earlier did not consistently improve final height, partly because the most severely affected children (salt-wasting form) were the ones treated earliest.
Fertility is a common concern but the picture is generally encouraging. In that same study, 18 out of 20 men evaluated had normal fertility, including five who had never been treated. Women with classic CAH may face more fertility challenges due to hormonal imbalances and sometimes anatomical factors, but many conceive successfully with proper management. Among women with nonclassic CAH, reduced fertility affects a smaller proportion, around 12% in one large study, and often responds to treatment adjustments.
Adrenal Crisis: The Emergency to Know About
Because people with classic CAH depend on replacement cortisol, any situation that increases the body’s cortisol demand can become dangerous. Illness, injury, surgery, or severe emotional stress can trigger an adrenal crisis, where the body simply doesn’t have enough cortisol to function. Signs include confusion, rapid heart rate, extreme fatigue, vomiting, low blood pressure, and in severe cases, loss of consciousness.
People with CAH and their families learn to increase their cortisol dose during illness or physical stress, a practice called “stress dosing.” Many also carry injectable emergency medication and wear medical alert identification. Adrenal crisis is the most acute risk of living with CAH, but with proper preparation it can be managed effectively.