ABCC6 and pseudoxanthoma elasticum (inherited or acquired): Further, the significant variability in clinical severity of the PXE phenotype cannot be explained by the ABCC6 mutations, as demonstrated by numerous negative genotype-phenotype correlation studies (Meloni et al., 2001; Gheduzzi et al., 2004; Chassaing et al., 2005; Pfendner et al., 2007).