21-hydroxylase deficiency (21-OHD) is an inherited disorder that results from a mutation on the CYP21A2 gene. It affects the adrenal glands and is the most common cause of congenital adrenal hyperplasia (CAH). 21-OHD CAH causes the body to produce an insufficient amount of cortisol and an excess of androgen, the type of hormone that produces male characteristics. The primary treatment for 21-OHD CAH, glucocorticoid replacement therapy, has been shown to cause bone loss. However, the elevated hormone levels caused by 21-OHD CAH may increase production of the protein osteoprotegerin (OPG), which in turn may protect against bone loss. This study will compare bone density and OPG levels in women who have 21-OHD CAH and have undergone a lifetime of glucocorticoid replacement therapy to that in women who have neither of these criteria. In doing so, the study will aim to determine the relationship between OPG and bone loss.

Because of the excess of androgen caused by 21-OHD CAH, women with CAH may exhibit some male-like characteristics. Glucocorticoids are a member of a class of drugs called corticosteroids, which are used in hormone replacement therapy. In order to counteract the effects of 21-OHD CAH, women with the disease are given hormone replacement therapy with glucocorticoids beginning at infancy. Glucocorticoids are known to cause bone loss. Despite many years of treatment with glucocorticoids, however, young women with 21-OHD CAH seem to be protected against bone loss. Researchers believe that the increased androgen levels in these women leads to increased estrogen levels, which in turn increases OPG production. The increase in OPG levels may protect women against bone loss. This study will evaluate bone density and OPG levels in women with and without 21-OHD CAH to determine the relationship between OPG and bone loss.

Participants in this observational study will attend only one study visit. At this visit, they will undergo a blood draw; a scan of their lower spine, hip, and forearm; height and weight measurements; and a body fat analysis test. This last test will entail a weak and painless electrical signal being sent from foot to foot. Participants will not attend any follow-up visits for this study.

Inclusion Criteria:

For People with 21-OHD CAH:

• 21-OHD CAH has been documented by molecular genetic analysis (mutations on CYP21A2 gene on both parental alleles)
• Treatment with glucocorticoid replacement since infancy (begun within the first year)
• Available hormonal data and treatment details over the 5 years prior to study entry
• Premenopausal

For Healthy Controls:

• No diagnosis of 21-OHD CAH, as confirmed by molecular genetic analysis
• No first degree relative is enrolled as a 21-OHD CAHparticipant
• Premenopausal

Exclusion Criteria:

• Medical disorder or treatment with medications known to affect bone density (other than glucocorticoids for 21-OHD CAH patients), including, but not limited to growth hormone, IGF-I, depo-medroxyprogesterone acetate, biphosphonates, oral contraceptives, androgens, thyroxine, or aromatase inhibitors
• Pregnant
• Any smoking within the 6 months prior to study entry
• Cardiac pacemaker or other implanted electronic medical device

Premenopausal women between the ages of 20 and 35 who have 21-OHD CAH or do not have 21-OHD CAH.