In addition, defective 17α-hydroxylase activity occurred in the presence of ∼70% of Cyp17a1 expression, despite 17α-hydroxylase deficiency being an autosomal recessive disease in which 50% of enzyme reduction has no major effect on the steroid metabolism [14]. This evidence concerns the gene CYP17A1 and hyperinsulinemic hypoglycemia, familial, 4.