Ehlers-Danlos syndrome: molecular and clinical characterization of TNXA/TNXB chimeras in congenital adrenal hyperplasia.

The syndrome CAH-X is due to a contiguous gene deletion of CYP21A2 and TNXB resulting in TNXA/TNXB chimeras.To analyze TNXB gene status and to clinically evaluate the Ehlers-Danlos syndrome phenotype in a large cohort of Argentine congenital adrenal hyperplasia (CAH) patients to assess the prevalence of this condition in our population.TNXB-gene analysis was performed in 66 non-related CAH patients that were carriers of the CYP21A2 gene deletion. A molecular strategy based on Multiplex ligation-dependent probe amplification and Sanger sequencing analysis was developed allowing for the detection of different, previously described TNXA/TNXB chimeras, named CH1, CH2, and CH3.TNXB status of CAH patients that were carriers of the CYP21A2 deletion in the homozygous or heterozygous state.TNXA/TNXB CH1 was found in 41%, CH2 in 29% and CH3 in 1.5% of non-related alleles carrying the CYP21A2 deletion. Thus, overall 71% of alleles were found to carry a contiguous gene deletion. 67% of patients analyzed had a monoallelic and 6% a biallelic form. All patients with the biallelic form had severe skin hyperextensibility and generalized joint hypermobility.Based on the high frequency of TNXB alterations in CYP21A2-deletion carrier alleles found, we recommend to evaluate TNXB status in these patients, and to assess connective tissue dysplasia including cardiologic alterations in positive cases. The number of patients undergoing cardiological evaluation should be expanded to determine the incidence of structural and functional abnormalities in this cohort.

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