PANK2 and pantothenate kinase-associated neurodegeneration: Since the number of PKAN patients in that study was small and not homogenous with respect to the underlying mutation of the PANK2 gene, the question remained whether the PKAN-associated acanthocytic state of erythrocytes is caused by specific Pank2 mutations or rather by some Pank2-independent, yet unknown factor(s).