CYP21A2 and congenital adrenal hyperplasia: Another example of how the clinical and/or phenotypic impact of a mutant gene can be nullified by a CNV is provided by a foetus that possessed paternal (Gln318Term) and maternal (Arg356Term) nonsense mutations of the CYP21A2 gene but lacked the normal clinical sequelae of congenital adrenal hyperplasia; this was found to be due to a duplication of the CYP21A2 gene on the paternal allele (Kleinle et al. 2009; Lekarev et al. 2013).