hyperkalemia. With appropriate treatment, most infants are out of danger within 24 hours. Virilization of female infants It is the 21-hydroxylase enzyme that is essential in conversion of progesterone and 17α-hydroxyprogesterone into 11-deoxycorticosterone and 11-deoxycortisol, respectively. This process is done through hydroxylation at C-21 position. It was described in at least 1953 that impaired steroid hydroxylation at C-21 position happens in congenital adrenal hyperplasia and is accompanied by excessive amounts of 17α-hydroxyprogesterone that leads to virilism. In the insufficiency of 21-hydroxylase to participate in the biosynthesis of cortisol, the 21-hydroxylation in the zona fasciculata of the adrenal cortex is impaired, so 17α-hydroxyprogesterone and progesterone will not be properly converted into 11-deoxycortisol and 11-deoxycorticosterone, respectively − the precursors for cortisol and aldosterone. As the plasma concentration of cortisol and aldosterone decreases, ACTH levels increase, leading to excessive production and accumulation of cortisol precursors (especially 17α-hydroxyprogesterone), which are eventually transferred to androsterone and testosterone. Other androgens may be additionally produced from 17α-hydroxyprogesterone, due to its elevated levels, that leads, inter alia, to its 5α-reduction. These additional androgens are produced via the so-called "backdoor pathway". For example, in this "backdoor" pathway, 5α-dihydrotestosterone is produced with roundabout of testosterone as an intermediate product. Some of the androgens produced by the backdoor pathway are those that cannot be converted to estrogens by aromatase, causing prenatal virilization, and making them the dominant androgens in classic 21-hydroxylase deficiency. Virilization of genetically female (XX) infants usually produces obvious genital ambiguity. Inside the pelvis, the ovaries are normal and since they have not been exposed to testicular antimullerian hormone (AMH), the uterus, fallopian tubes, upper vagina, and other mullerian structures are normally formed as well. However, the high levels of testosterone in the blood can enlarge the phallus, partially or completely close the vaginal opening, enclose the urethral groove so that it opens at the base of the phallus, on the shaft or even at the tip like a boy. Testosterone can cause the labial skin to become as thin and rugate as a scrotum, but cannot produce palpable gonads (i.e., testes) in the folds. Thus, depending on the severity of hyperandrogenism, a female infant can be mildly affected, obviously ambiguous, or so severely virilized as to appear to be a male. Andrea Prader devised the following Prader scale as a way of describing the degree of virilization. An infant at stage 1 has a mildly large clitoris and