ABCB6 and porphyria: In the severely affected porphyria patients, five heterozygous rare (minor allele frequency (MAF) <1%) and one heterozygous low-frequency (MAF <5%) variants in ABCB6 were identified, and the unimpaired ABCG2 V12M variant21 was found in four patients (Table 1; Supplementary Table 1).