GPX4 and hereditary spastic paraplegia 5A: Neurodegenerative multisystem disorders related to selenoproteins and their biosynthesis include autosomal recessive pontocerebellar hypoplasia type 2D due to SEPSECS deficiency13,25 (SEPSECS [MIM: 613811]), Sedaghatian-type spondylometaphyseal dysplasia due to GPX4 deficiency (GPX4 [MIM: 250220]),26 TXNRD1 deficiency (TXNRD1 [MIM: 601112]),27 and autosomal recessive spastic paraplegia 81 due to selenoprotein I deficiency (SELENOI [MIM: 618768]).22