Congenital adrenal hyperplasia is an autosomal recessive condition caused by single-gene defects in the enzymes involved in cortisol biosynthesis, most commonly 21-hydroxylase. Establishing the genetic cause can sometimes help predict disease severity and ensure accurate genomic counselling.

In many babies who present with ambiguous genitalia in the newborn period, there will be a genetic cause. Genetic sex needs to be established rapidly for management purposes.

Ambiguous genitalia can be detected during ultrasound, where the outer genitals do not have the typical appearance of either male or female.