In our publication we report two Polish female siblings diagnosed and treated at the Children’s Memorial Health Institute in Warsaw, Poland, with compound heterozygous mutations in POLR3B. They both presented with compatible clinical and MRI features of 4H leukodystrophy, together with polymicrogyria (PMG) and cataracts, which have been never reported in 4H patients before. This evidence concerns the gene POLR3B and polymicrogyria.