PEX6 and Zellweger spectrum disorders: Compound heterozygosity of the hypomorphic PEX6 c.1802G>A allele has been reported previously in seven individuals with a Zellweger spectrum disorder.20,23 In all reported individuals, the p.Arg601Gln allele was in trans with a severe PEX6 allele that, when homozygous or in trans with another severe PEX6 allele, causes a severe peroxisomal phenotype (six individuals) or that is predicted to be deleterious (one individual).