Advancing in Schaaf-Yang syndrome pathophysiology: from bedside to subcellular analyses of truncated MAGEL2

Abstract

ABSTRACTBackgroundSchaaf-Yang syndrome (SYS) is caused by truncating mutations in MAGEL2, mapping to the Prader-Willi region (15q11-q13), with an observed phenotype partially overlapping that of Prader-Willi syndrome. MAGEL2 plays a role in retrograde transport and protein recycling regulation. Our aim is to contribute to the characterization of SYS pathophysiology at clinical, genetic and molecular levels.MethodsWe performed an extensive phenotypic and mutational revision of previously reported SYS patients. We analysed the secretion levels of amyloid-β 1-40 peptide (Aβ1-40), and performed targeted metabolomic and transcriptomic profiles in SYS patients’ fibroblasts (n=7) compared to controls (n=11). We also transfected cell lines with vectors encoding wild-type (WT) or truncated MAGEL2 to assess stability and subcellular localization of the truncated protein.ResultsFunctional studies show significantly decreased levels of secreted Aβ1-40 and intracellular glutamine in SYS fibroblasts compared to wild-type. We also identified 132 differentially expressed genes, including ncRNAs such as HOTAIR, many of them related to developmental processes and mitotic mechanisms. The truncated form of MAGEL2 displayed a stability similar to the wild-type but it was significantly switched to the nucleus, compared to a mainly cytoplasmic distribution of the wild-type MAGEL2. Based on updated knowledge we offer guidelines for clinical management of SYS patients.ConclusionA truncated MAGEL2 protein is stable and localises mainly in the nucleus, where it might exert a pathogenic gain of function effect. Aβ1-40 secretion levels and HOTAIR mRNA levels might be promising biomarkers for SYS. Our findings may improve SYS understanding and clinical management.Key MessagesMAGEL2 truncating mutations cause Schaaf-Yang syndrome (SYS) but the functional effects of the truncated MAGEL2 protein have been poorly defined. By expressing truncated MAGEL2 in cell lines, we now know that a truncated version of the protein is retained in the nucleus, thus exerting a gain-of-function behaviour in addition to the loss of some of its main functions. Patients’ fibroblasts show reduced levels of excreted amyloid beta 1-40 and intracellular glutamine as well as an altered transcriptomic profile, including overexpression of the major regulator HOTAIR. Based on a comprehensive review of genetic and clinical aspects of all reported cases, families and physicians will benefit from the Clinical Management Recommendations that we provide here.