SLC7A6OS (solute carrier family 7 member 6 opposite strand) is a conserved vertebrate gene that directs RNA polymerase II nuclear import and plays a critical role in central nervous system (CNS) development. The gene encodes a protein with functional homology to yeast Iwr1, which specifically binds RNA polymerase II and regulates transcription of specific genes 1. During zebrafish development, slc7a6os is maternally expressed with prevalent localization in the developing CNS; knockdown results in morphological defects including poorly defined midbrain-hindbrain interfaces, altered somite morphology, and immobility, with disrupted expression of CNS-specific marker genes pax2a and neurod 1. These developmental phenotypes are rescued by synthetic mRNA co-injection, confirming slc7a6os function in regulating key developmental genes 1. Biallelic loss-of-function variants in SLC7A6OS cause progressive myoclonic epilepsy (PME12). A homozygous splice-site variant (c.191A>G) identified in two unrelated families with PME12 abolishes normal splicing, creates an abnormal isoform, and causes marked reduction in protein expression 2. This genetic evidence establishes SLC7A6OS as a novel disease gene for progressive myoclonus epilepsy, likely through disrupted CNS development or transcriptional regulation.