Two CAH-X chimeras account for the vast majority of CAH-X genotypes and also represent 30% of 30-kb deletions, or 15% of all CAH alleles: CAH-X CH-1 substitutes TNXA for TNXB exons 35–44, resulting in a null allele; while CAH-X CH-2 substitutes TNXA for TNXB exons 40–44, resulting in a dominant negative effect [8]. This evidence concerns the gene TNXB and congenital adrenal hyperplasia.