The New York Times this week has
a very nice article about Congenital Adrenal Hyperplasia or CAH, as it is called. I thought the article was very well-written, but might be confusing for folks who don't know the basics about CAH, and might lead some women to over-diagnose themselves with what is a rather uncommon condition. So let me see if I can give you the basics and help you put the article in perspective.
Congenital Adrenal Hyperplasia (CAH)CAH is caused by a genetic enzyme abnormality in the adrenal gland. In women, this can lead to an over-production of testosterone, which in turn can cause irregular menses, acne, hirsutism (excess hair growth) and infertility.
Clinically, CAH is classified in decreasing order of severity as -
Classical salt-wasting CAH (Early onset): Presenting at birth with varying degrees of genital ambiguity in females (normal genitals in males), severe adrenal insufficiency and life-threatening salt wasting (both males and females). It is treated with lifelong steroids. Females have normal internal genital structures and with treatment can have normal menstrual cycles and normal pregnancies. Hirsutism can be problematic but is usually quite treatable. Surgery is usually done to correct the genital abnormalities.
Non-classical, virilizing CAH - Enough adrenal steroids are produced to prevent adrenal insufficiency and genitals are normal at birth. Elevated testosterone levels can causes early puberty and in girls, excess hair growth and clitoral enlargement.
Late-onset, non-classical CAH - Presents in the late teens and 20's with menstrual irregularities, severe acne or hirsutism, and sometimes, infertility. Can also cause early puberty, though this is less common. Can have no symptoms at all.
The condition the NY Times article is addressing is late onset or non-classical CAH. So that's what we'll be talking about in the rest of this post.
Genetics of CAH
The gene affected in CAH is called CYP21A2, and it codes for the enzyme 21-hydroxylase. This enzyme is part of the adrenal production pathway for cortisol, and catalyzes the conversion of 17-hydroxyprogesterone to 11-deoxycortisol. (It's the second vertical green bar on the top in the steroid production pathway up there.) If that enzyme is blocked, levels of 17 hydroxyprogesterone build up, and then steroid production tends to preferentially head down the other path towards testosterone.
Think of it as a construction delay at the Manhattan-bound Lincoln Tunnel, with cars backed up all the way to the Jersey Turnpike. Traffic is so hemmed in that you can't get over to the right lane, and you end up on Rte 3 headed to Secaucus (testosterone) instead of Manhattan (cortisol). Not exactly where you wanted to go, was it?
CYP21A2 is a recessive gene, meaning that an individual usually has to carry two abnormal gene copies to be affected. There are several different known mutations of the gene, some leading to more severe enzyme deficiencies than other, and various combinations of these mutations in an individual can lead to varying degrees of severity of the condition. The correlation between a specific CYP21A2 mutation and clinical presentation is not always predictable, and other genes are thought to influence the phenotypic presentation.
How common is late-onset or non-classical CAH?
The Times article states that CAH is much more common than realized, and not diagnosed or treated as often as it should be.
Dr. New, who has studied the disease among New Yorkers, said she found it in 1 out of 100 people, but more often in certain ethnic groups — 1 in 27 Ashkenazi Jews, for example, and 1 in 40 Hispanics. It is the most common of the autosomal recessive diseases, in which a child inherits two copies of a recessive gene from his parents — a class that includes sickle cell anemia, Tay-Sachs and cystic fibrosis.
Remember that Dr New screens a select population of women and New Yorkers, so those numbers are not necessarily representative of the US population at large. I've been screening for late-onset CAH for over 20 years whenever an adolescent or adult woman presents to me with irregular menses and acne or hair growth, and I've diagnosed it in maybe 2 or 3 patients. It just is not very common. Be careful also not to confuse the incidence of the gene defect with the clinical condition - not all women who have the gene defect have any symptoms.
As an aside, I've probably seen more classic CAH patients in my career than most gynecologists, having done the pelvic exams as part of a long term study of classical CAH patients conducted by Dr New.
Screening for late-onset CAH
The screen for late-onset CAH is a simple blood test for 17 hydroxyprogesterone - that hormone builds up as a result of the mild enzyme block in the adrenals. It should be done whenever a woman presents with menstrual irregularities and signs of excess androgens such as hirsutism or severe acne. (The test has a very low yield in the absence of signs of androgen excess, but may be useful in evaluating infertility if severe menstrual irregularities are present or there is no response to standard treatments.).
Testing for 17 hydroxy-progesterone is best done fasting and in the latter part of the menstrual cycle. If the result is abnormally high, then a confirmatory test is done called an ACTH stimulation test. The patient is given a hormone that stimulates the adrenal gland to make more steroids, leading to more back up behind the enzyme block and a further rise in 17 hydroxy progesterone. (Think of the ACTH stim test as causing rush hour traffic in the analogy I gave above.)
How is CAH Treated?
Treatment of late-onset CAH depends on the desired outcome and severity of symptoms. If the menstrual cycles are fairly regular and hirsute symptoms mild, then no treatment is necessarily needed. Birth control pills are the mainstay of treatment for mild forms of the condition, especially in sexually active women who want to prevent pregnancy. More severe forms will respond to steroids with or without oral contraceptives. Women who want to conceive may be treated with steroids or not depending again on how severe the condition is and how well she responds to standard ovulation induction.
What about Genetic Testing?
Because the CYP21A2 gene is recessive, individuals who carry the gene may not be aware of it. If two carriers have a child, there is a 25% chance they will have a child with the more severe classical form of the disorder.
Which leads of course to the question - who should be screened for the CAH gene defect?
I'd recommend screening if anyone in your immediate family has CAH - you could be a gene carrier. If you are, then your husband can be screened before you get pregnant to determine if you are at risk for having a child with the classical form of CAH. Given the incidence of CAH in Ashkenazi Jews, I suspect at some point we may start offering CAH testing along with Tay Sachs and other genetic prenatal screens. Right now, however, it is not a recommended routine test in this population.
For more information on CAH