GTPBP2 and neurodegeneration with brain iron accumulation: GTPBP1 variants have not been reported before in humans, and so there is no known Mendelian disease associated with genetic defects in GTPBP1. The GTPBP2-related NDDs have been recently described in a limited number of families with clinical manifestations that are almost identical to GTPBP1. The first reported family was found to carry a homozygous (splicing) variant in GTPBP2 and associated MRI findings of NBIA.