Premature atherosclerosis is also associated with mutations in the "ABCC6" gene, even in those without PXE. A syndrome almost indistinguishable from hereditary PXE has been described in patients with hemoglobinopathies (sickle-cell disease and thalassemia) through a poorly understood mechanism. In addition, there appears to be another PXE-like syndrome with a similar phenotype but as a result of problems with another gene, gamma-glutamyl carboxylase. Mutations in "ABCC6" can also cause generalized arterial calcification of infancy. In some cases of PXE, mutations in "ABCC6" cannot be found, and other genes such as "ENPP1" may be implicated