PANK2 and pantothenate kinase-associated neurodegeneration: Two PKAN patients, patient 1 (P1) and patient 2 (P2), carried double heterozygous pathogenic variants showing low residual PANK2 expression levels, while patient 3 (P3) carried a frameshift pathogenic variant in both alleles that results in a truncated PANK2 protein and ultimately, in a total absence of protein expression.