Catalyzes the side-chain cleavage reaction of cholesterol to pregnenolone. Defects in CYP11A1 are the cause of adrenal insufficiency congenital with 46,XY sex reversal (AICSR). A rare disorder that can present as acute adrenal insufficiency in infancy or childhood. ACTH and plasma renin activity are elevated and adrenal steroids are inappropriately low or absent; the 46,XY patients have female external genitalia, sometimes with clitoromegaly. The phenotypic spectrum ranges from prematurity, complete underandrogenization, and severe early-onset adrenal failure to term birth with clitoromegaly and later-onset adrenal failure. Patients with congenital adrenal insufficiency do not manifest the massive adrenal enlargement typical of congenital lipoid adrenal hyperplasia. Belongs to the cytochrome P450 family. Note: This description may include information from UniProtKB.