NSRP1 (Nuclear Speckle Splicing Regulatory Protein 1) is an RNA-binding protein that regulates alternative pre-mRNA splicing with critical roles in development and disease. The protein functions as a splicing regulator in nuclear speckles, controlling the alternative processing of various RNA splicing factors including the oncogenic factor SRSF1 1. NSRP1 demonstrates tissue-specific expression patterns, being selectively expressed in developing thymocytes where it controls cell cycle and survival during T cell maturation 1. In breast cancer, NSRP1 acts as a tumor suppressor by regulating alternative splicing of genes like NUMB and NSD2, influencing interferon signaling pathways and epithelial-mesenchymal transition 23. Mechanistically, NSRP1 requires proper nuclear localization through C-terminal nuclear localization signals for function 45. Biallelic loss-of-function variants in NSRP1 cause a severe autosomal recessive neurodevelopmental disorder characterized by developmental delay, epilepsy, microcephaly, hypotonia, and spastic cerebral palsy 5. Milder phenotypes can result from missense variants affecting nuclear localization 4. The gene also hosts miR-423-5p, which regulates cardiac pacemaking through HCN4 targeting 6.