Characterization of the structural aberrations and mutations of the RCCX module in patients with Congenital Adrenal Hyperplasia and Ehlers-Danlos syndromes. W. Chen¹, J. Yang¹, M. Berk², C. VanRyzin², D. Merke², N.B. McDonnell¹ 1) Lab Clinical Investigation, NIA/NIH, Baltimore, MD; 2) NICHD/NIH, Bethesda, MD.

   The gene2 encoding 21-hydroxylase (CYP21A2) and Tenascin-X (TNXB) are located within the HLA complex on chromosome 6, in a region of high gene density termed the RCCX module. The region has multiple pseudogenes as well as tandem repeat sequences that promote misalignment during meiosis leading to complex gene rearrangements, deletions and gene conversion events. CYP21A2 mutations cause Congenital Adrenal Hyperplasia (CAH) and TNX deficiency has been proposed as a cause of hypermobile Ehlers-Danlos syndrome (EDS). We investigated the structure of the RCCX module in a cohort of CAH patients seen at the National Institute of Child Health and Development, and in Ehlers-Danlos patients seen at the National Institute on Aging. Southern blotting, PCR-based detection of deletions, and direct sequencing of exons of interest were utilized. A novel heterozygous 30 kB TNXB deletion that did not extend into CYP21A2 was found in a family with hypermobile form of EDS. CYP21A2 deletions were detected in 30% of the subjects in the CAH cohort, 25% of those subjects had a deletion extending into TNXB. Unusual haplotypes including three CAH probands with triplication of CYP21A2, and a sibling pair with a deletion of TNXB and triplication of CYP21A2 were identified through Southern Blot analysis. A novel mutation in a CAH family with joint hypermobility was detected in exon 8 of TNXB (c.G3452>A Arg1151His). This mutation involves the highly conserved fibronectin type III repeat in TNXB which is known to be involved in collagen fibrillogenesis, and was not seen in control subjects.