What is Congenital Adrenal Hyperplasia?

Congenital Adrenal Hyperplasia (CAH) refers to syndromes caused by an inherited defect in an enzyme involved in the production of cortisol and aldosterone and are the commonest adrenal disorders of infancy. There are two major consequences of a defect in any of these pathways:

  1. A decreased negative feedback inhibition on ACTH release from the pituitary. This will result in excess ACTH release.
  2. There will be excessive stimulation of other ACTH-dependent pathways unaffected by the defect. Therefore an accumulation of excess androgen (male sex steroids) and mineralocorticoids usually develops.

The prolonged ACTH hyperstimulation results in hyperplasia of the adrenals and hence the name of the condition - Congenital Adrenal Hyperplasia.

In order to fully understand how the defects result in the accumulation of different hormones, it is important to understand the basic principles of the cortisol, aldosterone and sex steroid biosynthesis.

An outline of the biosynthesis pathways

An outline of the biosynthesis pathways - click to enlarge

The basic principle is that cholesterol is converted into various hormones by the actions of different enzymes. As these enzymes act in pathways, a deficiency at any point will result in both the accumulation of hormones before that point and a reduction of hormones after.

The possible types are:

  • 21-hydroxylase deficiency
  • 11ß-Hydroxylase deficiency
  • 17-hydroxylase deficiency
  • 3ß-dehydrogenase deficiency

These are all dealt with in their own sections.