[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Endocrine system](https://durgical.com/en/general-pathology/areas/endocrine/) › Congenital adrenal hyperplasia

# Congenital adrenal hyperplasia

- Mechanism

In congenital adrenal hyperplasia, a missing enzyme blocks cortisol production. The adrenals grow and make extra male hormones instead.

Updated Nov 12, 2026

## Key points

- Autosomal recessive; 21-hydroxylase (CYP21A2) deficiency is the commonest.
- Classic salt-wasting form: no cortisol or aldosterone, adrenal crisis in the first weeks, hyponatraemia, hyperkalaemia; ambiguous genitalia in 46,XX girls.
- Simple virilising form: enough aldosterone, but androgen excess.
- Non-classic (late-onset): hirsutism, acne, oligomenorrhoea; mimics PCOS.
- 11-beta-hydroxylase deficiency: virilisation plus hypertension (11-deoxycorticosterone excess).
- 17-alpha-hydroxylase deficiency: no androgens or cortisol, hypertension, hypokalaemia, and undervirilised 46,XY or absent puberty.

## What it is

Adrenogenital syndromes are disorders of androgen excess from the adrenal cortex, caused by tumours or, most often, by congenital adrenal hyperplasia (CAH). CAH is a group of autosomal recessive defects of cortisol synthesis. Low cortisol raises ACTH, which drives bilateral hyperplasia and pushes precursors into the androgen pathway. 21-hydroxylase deficiency causes the great majority of cases and is detected by newborn screening in many countries.

## Structure

- Both adrenals are enlarged, sometimes many times normal, with a thick brown cortex (lipid-depleted compact cells).
- Pituitary: corticotroph hyperplasia.
- Adrenal rest tumours of the testis can form from ACTH-driven ectopic adrenal tissue.

## Step by step

- An enzyme defect blocks the cortisol pathway.
- Low cortisol removes negative feedback: ACTH rises.
- ACTH stimulates bilateral cortical hyperplasia.
- Precursors before the block accumulate and are shunted into the androgen (or mineralocorticoid) pathway.
- Effects depend on the enzyme: androgen excess, salt loss or salt retention.

## Three enzyme defects compared

| Enzyme | Mineralocorticoid | Androgens | Blood pressure | Clue |
| --- | --- | --- | --- | --- |
| [21-hydroxylase](https://durgical.com/en/conditions/adrenal-crisis/) | Low (salt wasting in classic form) | High | Low | High 17-hydroxyprogesterone; virilised girls |
| 11-beta-hydroxylase | 11-deoxycorticosterone high | High | High | Virilisation with hypertension |
| 17-alpha-hydroxylase | 11-deoxycorticosterone high | Low | High | Hypokalaemia; no puberty; undervirilised boys |

## Clinical notes

- Salt-wasting crisis in a newborn can be fatal if missed; boys may look normal at birth.
- Androgen excess accelerates growth but closes growth plates early: short adult stature.
- Other adrenogenital causes: androgen-secreting adrenocortical carcinoma (usually) or adenoma.

## Memory aid

Numbers ending in 1 (21 and 11) virilise; 17 takes the androgens away; and only 11 and 17 push the blood pressure up.

## Test yourself

Think of the answer, then tap the question to see it.

## Why are the adrenals enlarged in congenital adrenal hyperplasia?

Low cortisol removes feedback on the pituitary; high ACTH drives bilateral cortical hyperplasia.

## Which CAH form causes virilisation and hypertension?

11-beta-hydroxylase deficiency, through excess 11-deoxycorticosterone and androgens.

## Which steroid is high in 21-hydroxylase deficiency and used for screening?

17-hydroxyprogesterone.

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## Elsewhere in DurgiPedia

- [Differences of sex development: CAH, AIS and 5α-reductase](https://durgical.com/en/embryology/differences-of-sex-development-cah-ais-and-5-reductase/)
- [Adrenal cortisol synthesis](https://durgical.com/en/biochemistry/pathways/adrenal-cortisol-synthesis/)
- [21-Hydroxylase (CYP21A2)](https://durgical.com/en/biochemistry/enzymes/21-hydroxylase/)
- [11β-Hydroxylase (CYP11B1)](https://durgical.com/en/biochemistry/enzymes/11-hydroxylase/)
- [17α-Hydroxylase/17,20-lyase (CYP17A1)](https://durgical.com/en/biochemistry/enzymes/17-hydroxylase-17-20-lyase/)

## Connections

## Related 3

- [Adrenocortical insufficiency](https://durgical.com/en/general-pathology/adrenocortical-insufficiency/)
- [Adrenocortical adenoma and carcinoma](https://durgical.com/en/general-pathology/adrenocortical-adenoma-and-carcinoma/)
- [Hyperplasia: physiologic and pathologic](https://durgical.com/en/general-pathology/hyperplasia-physiologic-and-pathologic/)

## Related conditions 4

- [Adrenal crisis](https://durgical.com/en/conditions/adrenal-crisis/)
- [Adrenal insufficiency](https://durgical.com/en/conditions/adrenal-insufficiency/)
- [Polycystic ovary syndrome](https://durgical.com/en/conditions/polycystic-ovary-syndrome/)
- [Androgen insensitivity syndrome](https://durgical.com/en/conditions/androgen-insensitivity-syndrome/)

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Congenital adrenal hyperplasia: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000411.htm) (MedlinePlus, US National Library of Medicine, 2025); [21-hydroxylase deficiency](https://medlineplus.gov/genetics/condition/21-hydroxylase-deficiency/) (MedlinePlus, US National Library of Medicine, 2025); [Congenital adrenal hyperplasia due to 11-beta-hydroxylase deficiency: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/congenital-adrenal-hyperplasia-due-to-11-beta-hydroxylase-deficiency/) (MedlinePlus, US National Library of Medicine, 2025).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/general-pathology/congenital-adrenal-hyperplasia/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/congenital-adrenal-hyperplasia/