What is Congenital Adrenal Hyperplasia?
Congenital Adrenal Hyperplasia (CAH) is a group of inherited disorders that affect how the adrenal glands make hormones.
The adrenal glands normally produce three important groups of hormones:
In CAH, one of the enzymes needed to make these hormones does not work properly. This creates a "traffic jam" in hormone production. The body cannot make enough cortisol, and in some forms, not enough aldosterone. Instead, hormone production is diverted toward making excess adrenal androgens.
The Most Common Type
Around 90–95% of CAH cases are caused by a deficiency of the enzyme 21-hydroxylase.
This enzyme is essential for producing both cortisol and aldosterone.
When it is missing:
Although other, rarer forms of CAH exist, 21-hydroxylase deficiency accounts for the vast majority of cases seen in children.
How Is CAH Inherited?
CAH is an autosomal recessive genetic condition.
This means that:
Families are often surprised by the diagnosis because there may be no previous history of the condition.
What Happens Inside the Body?
The brain constantly monitors cortisol levels.
When cortisol is low, the pituitary gland releases more ACTH (adrenocorticotropic hormone) to stimulate the adrenal glands.
However, because the enzyme defect remains, the adrenal glands still cannot produce enough cortisol.
Instead:
This explains both the name Congenital Adrenal Hyperplasia and many of the clinical features.
The Two Major Forms of CAH
1. Salt-wasting CAH
This is the most severe and potentially life-threatening form.
Children have:
Without aldosterone, the kidneys lose excessive amounts of sodium and water. This can lead to:
Salt-wasting crises usually develop during the first one to three weeks of life.
Without treatment, they can be fatal.
2. Simple Virilising CAH
Children still have low cortisol and excess adrenal androgens, but retain enough aldosterone to avoid severe salt loss.
These children may not present in the newborn period. Instead, they may develop:
Although they are often taller than peers during early childhood, untreated children may ultimately become shorter adults because the growth plates mature and close too early.
How Does CAH Present in Newborns?
Girls
Excess adrenal androgens before birth may cause varying degrees of virilisation of the external genitalia.
This may include:
Importantly:
The appearance of the genitalia often leads to early diagnosis.
Boys
Newborn boys usually have normal-appearing genitalia.
Because there are no obvious external signs, diagnosis can be delayed until the baby develops:
This is why boys with CAH are at particular risk of presenting in adrenal crisis if newborn screening is not available.
Can CAH Be Detected at Birth?
Many countries like Singapore include CAH in their newborn screening programmes.
A small blood sample taken from the baby's heel is analysed for elevated hormone precursors.
Early detection allows treatment to begin before a salt-wasting crisis develops.
Where screening is not available, recognising the symptoms becomes even more important.
How Is CAH Diagnosed?
Doctors combine:
Ultrasound may also be used to assess the internal reproductive organs in girls with atypical genitalia.
How Is CAH Treated?
Treatment replaces the hormones that the body cannot produce.
Most children require:
During illness, surgery, or injury, children also require stress-dose hydrocortisone, as discussed in the previous post.
Treatment requires lifelong follow-up with a paediatric endocrinology team.
Will Children with CAH Grow and Develop Normally?
With modern treatment, the outlook for children with CAH has improved dramatically.
Most children:
Regular follow-up is important to ensure:
The goal is not simply survival—it is helping children thrive.
When Should Parents Seek Medical Attention?
Seek urgent medical review if a newborn develops:
In older children with known CAH, seek immediate medical attention if illness is accompanied by:
Closing Thought
Congenital Adrenal Hyperplasia is one of the most important adrenal conditions diagnosed in childhood.
Although it is rare, recognising it early can prevent life-threatening complications.
With appropriate treatment, education, and regular follow-up, children with CAH can lead healthy, active lives.
For parents, knowledge is one of the most powerful treatments of all.