Diminished 5alpha-reductase activity in extracts of fibroblasts cultured from patients with familial incomplete male pseudohermaphroditism, type 2.

The activity of 5alpha-reductase, the enzyme that converts testosterone to dihydrotestosterone, has been assessed in cell-free extracts of fibroblasts grown from foreskin, labia majora, scrotum, and nongenital skin from control subjects, from patients with developmental defects of the urogenital system, drom two subjects with the type 2 form of familial incomplete male pseudohermaphroditism and from individuals with other forms of hereditary male pseudohermaphoditism. Enzyme activity was shown to be maximal in the pH range of 5 to 6. Substrate specificity studies indicated that the enzyme so assayed is the 5alpha-reductase previously characterized in human foreskin. The activity of the enzyme was low in normal fibroblasts grown from nongenital skin and high in most fibroblasts grown from genital skin. 5alpha-Reductase activity in extracts of foreskin fibroblasts from two subjects with the type 2 disorder was undetectable at pH 5.5. Activity in comparable fibroblast extracts from most patients with other forms of hereditary male pseudohermaphroditism was easily measurable.