17-OH Progesterone, LC/MS

Congenital adrenal hyperplasia (CAH), is an autosomal recessive disorder affecting one of the enzymes required to synthesize cortisol from cholesterol in the adrenal gland.^1-4 Diminished production of cortisol leads to increased pituitary secretion of ACTH via the negative feedback mechanism, which in turn causes hyperplasia of the adrenal cortex. Excess production of hormones proximal to the enzymatic defect gives rise to various clinical phenotypes. The clinical symptoms of CAH directly result from either the deficiencies in mineralocorticoid or glucocorticoid production or from the overproduction of precursors that are converted to androgens.^1-4 There is a wide spectrum of clinical presentations, including a severely affected, "salt-wasting" form, a simple virilizing form with normal aldosterone production, and a mild "nonclassic" form that may be asymptomatic or may be associated with symptoms that may not be discovered until adulthood.^1-5

The incidence of classic CAH ranges from 1:10,000 to 1:20,000 births¹ but is more prevalent in some ethnic groups, particularly in remote geographic regions. The most common form of CAH occurs as the result of mutations in the CYP21A2 gene, which results in 21-hydroxylase deficiency (21-OHD).¹ This enzyme converts 17-hydroxyprogesterone (17-OHP) to 11-deoxycortisol and progesterone to deoxycorticosterone, respective precursors for cortisol and aldosterone. In Caucasians, 21-OHD accounts for more than 90% of all cases, whereas 5% are caused by 11-hydroxylase deficiency and other enzyme deficiencies and clinical phenotypes are less common.^1,4 In 21-OHD, reduced production of glucocorticoids can lead to adrenal crises with hypoglycemia and hypotension in the setting of an illness or physiological stress.² Approximately 75% of classic CAH cases also suffer aldosterone deficiency with clinical symptoms that can include poor feeding and failure to thrive, vomiting, hyperkalemia, hyponatremia, dehydration, metabolic acidosis, and apathy.^1-4 The excess 17-OHP and other unblocked precursors, pregnenolone and progesterone, are diverted in the adrenals to the production of dehydroepiandrosterone and androstenedione, which are then peripherally converted to testosterone.^1,2 A key manifestation of this androgen overproduction is in utero virilization resulting in genital ambiguity in newborn females.^1-4 In fact, 21-OHD is the most common cause of ambiguous genitalia in females.⁸ Males with 21-OHD appear normal at birth so the age at diagnosis in untreated boys varies according to the severity of disease.^1-4 If unrecognized and left untreated, both girls and boys undergo rapid postnatal growth and sexual precocity as well as premature maturation of the growth plates, ultimately resulting in reduced final height.^1-4

Neonatal screening and diagnosis of CAH is typically accomplished through the measurement of 17-OHP by immunoassay from filter paper (Guthrie) cards with subsequent confirmation in serum by liquid chromatography/tandem mass spectrometry (LC/MS-MS).⁵ In order to reduce the potential of false-negative results, the cutoff levels of neonatal 17-OHP screening assays are typically set so that approximately 1% of all tests are reported as positive. Given the low prevalence of CAH, only approximately one in every 100 neonates with a positive screening test will have CAH as confirmed by LC/MS-MS.^1-5

Standard medical treatment of CAH consists of oral glucocorticoid and mineralocorticoid administration in order to suppress adrenal androgens and to compensate for adrenal steroid deficiencies.^1-5 Levels of 17-OHP, androstenedione, and plasma renin activity can be used to evaluate adequacy of therapy in conjunction with clinical signs and symptoms.⁸ A recent clinical practice guideline recommends monitoring treatment by measuring 17-OHP levels early in the morning and before medication.¹ This guideline states that 17-OHP should not be completely normalized because of risk of iatrogenic Cushing's syndrome.^1,8 The target 17-hydroxyprogesterone range suggested for children with CAH is 400−1200 ng/dL.⁸ Clinical factors dictate management of individual adults.⁸

In addition to the classic salt-wasting and simple virilizing forms of CAH, there is also a mild "nonclassic" form of CAH (NC-CAH), which may show variable degrees of postnatal androgen excess but is sometimes asymptomatic.^1,2,8 NC-CAH is much more common than classic CAH, occurring in approximately 0.1% to 0.2% in the general Caucasian population but in as much as 2% in some populations, such as Ashkenazi Jews.¹ NC-CAH presents with a wide spectrum of phenotypes due to the complexity of gene duplications, deletions, rearrangements, and compound heterozygotes that cause the condition.¹ Like more severe forms of CAH, NC-CAH can present as salt-wasting and simple virilizing disease with growth acceleration, premature adrenarche, or menstrual abnormalities.² NC-CAH is a relatively common cause of hyperandrogenic symptoms in women and has been implicated in between 2% and 5% of cases studied.^9-11 The diagnosis of nonclassic CAH after infancy is accomplished by measuring an early morning baseline serum 17-OHP in symptomatic individuals.^1-5,8 Measurement of other steroids after a cosyntropin stimulation can be used to differentiate 21-OHD from 11-hydroxylase and P450 oxidoreductase deficiencies and to make the diagnosis in borderline cases.^1-5,8