There is an article on the internet, that tends to disappear and reappear, but in essence it said that carriers of CAH have a significantly elevated cortisol responses. This means that carriers are able to respond more quickly to stress situations.

The paper was by Drs. Witchel, Lee, Suda-Hartman, Massimo, Trucco and Hoffman, of the Children’s Hospital of Pittsburgh and the Department of Molecular Genetics and Biochemistry of the Universtiy of Pittsburgh.

I found a brief synopsis of the study at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9215278&dopt=Abstract

which goes as follows:

Evidence for a heterozygote advantage in congenital adrenal hyperplasia due to 21-hydroxylase deficiency.

Witchel SF, Lee PA, Suda-Hartman M, Trucco M, Hoffman EP.

Division of Endocrinology, University of Pittsburgh, Pennsylvania 15213, USA.

21-Hydroxylase deficiency is one of the most common inherited disorders, with carrier frequencies of approximately 10% in all world populations studied to date. The high prevalence of the mutant gene is probably due to a flanking pseudogene serving as a reservoir for mutations. Despite the potential for a high rate of de novo mutations, a founder effect for specific gene conversions is observed in most populations. We hypothesized that there was a survival advantage to 21-hydroxylase heterozygotes, and here we report endocrinological and molecular investigations to test this hypothesis. We defined 28 carriers and 22 mutation-negative controls by molecular genotyping and determined ACTH-stimulated adrenal hormone responses. We found significantly elevated cortisol responses in the carriers compared to controls (30 min cortisol levels: normal, 24.2 +/- 4.6 micrograms/dL; carrier, 28.1 +/- 4.2 micrograms/dL; P < 0.005). Cortisol has a crucial role in maintaining homeostasis, influencing differentiation, suppressing inflammation, and effecting cross-talk among the immune, nervous, and endocrine systems. The brisk cortisol response we have documented in carriers of 21-hydroxylase may enable a rapid return to homeostasis in response to infectious, inflammatory, or other environmental stresses and may protect from inappropriate immune responses, such as autoimmune diseases.

The full text can be found at http://jcem.endojournals.org/cgi/content/full/82/7/2097 for the time being, if you want to check it out. I saved it to my hard drive in case it disappears again.