The most common group of disorders of the type are due to C21- hydroxylase deficiency. This results in an inability to produce cortisol and in an increase in ACTH levels, which leads to adrenocortical hyperplasia and to excessive production of androgens.
This in turn results in virilisation of the external genitalia in the female foetus, and precocious pseudopuberty in male infants. If the deficiency extends to the zona glomerulosa P450 C21, deficiency of aldosterone production with salt loss will also occur. This can result in adrenocortical deficiency or crisis, neonatally or later in life. In this disorder, the substrate for the defective enzyme is 17-hydroxyprogesterone (see Fig. 7.12), and synthesis of this steroid, and its plasma levels, will increase.
