Reciprocal and non-reciprocal effects of clinically relevant SETBP1 protein dosage changes

Many genes in the human genome encode proteins that are dosage sensitive, meaning they require protein levels within a narrow range to properly execute function. To investigate if clinically relevant variation in protein levels impacts the same downstream pathways in human disease, we generated cell models of two SETBP1 syndromes: Schinzel-Giedion Syndrome (SGS) and SETBP1 haploinsufficiency disease (SHD), where SGS is caused by too much protein, and SHD is caused by not enough SETBP1. Using patient and sex-matched healthy first-degree relatives from both SGS and SHD SETBP1 cases, we assessed how SETBP1 protein dosage affects downstream pathways in human forebrain progenitor cells. We find that extremes of SETBP1 protein dose reciprocally influence important signalling molecules such as AKT, suggesting that the SETBP1 protein operates within a narrow dosage range and that extreme doses are detrimental. We identified SETBP1 nuclear bodies as interacting with the nuclear lamina and suggest that SETBP1 may organize higher order chromatin structure via links to the nuclear envelope. SETBP1 protein doses may exert significant influence on global gene expression patterns via these SETBP1 nuclear bodies. This work provides evidence for the importance of SETBP1 protein dose in human brain development, with implications for two neurodevelopmental disorders.