Congenital adrenal hyperplasia - steroidogenesis pathway blocks (21-hydroxylase, 11-hydroxylase)
Core concept
- A block in cortisol synthesis -> dec negative feedback -> inc ACTH -> adrenal hyperplasia + accumulation of precursors proximal to the block
- The precursors are shunted down the unblocked pathway - usually into androgens
- Predict the phenotype from three questions
- Is cortisol made? (always no, by definition)
- Is ALDOSTERONE made? -> salt-wasting vs not
- Are ANDROGENS made? -> virilisation vs under-virilisation
| Enzyme | Cortisol | Mineralocorticoid | Androgen | Phenotype |
|---|---|---|---|---|
| 21-hydroxylase (CYP21A2) - 90-95% | dec | dec | inc | Salt-wasting + virilisation of females |
| 11-beta-hydroxylase (CYP11B1) - 5% | dec | inc DOC -> HYPERTENSION | inc | Hypertension + virilisation |
| 17-alpha-hydroxylase (CYP17A1) | dec | inc DOC -> HYPERTENSION | dec | Hypertension + UNDER-virilisation, absent puberty |
| 3-beta-HSD | dec | dec | Weak (DHEA) | Salt-wasting; mild virilisation of females, under-virilisation of males |
| StAR / lipoid CAH | dec | dec | dec | Severe salt-wasting, phenotypic female |
- *The two hypertensive forms are 11-beta and 17-alpha* - deoxycorticosterone is a potent mineralocorticoid
3 more sections, plus exam facts
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