The complex genetic structure of the RCCX CNV complicates further the genetic diagnosis of 21-hydroxylase deficiency, in particular when a haplotypic structure with the segment harboring two CYP21A2 gene copies and one CYP21A1P pseudogene copy is involved [6]. The gene discussed is CYP21A2; the disease is classic congenital adrenal hyperplasia due to 21-hydroxylase deficiency.