Metabolic biomarker testing facilitates genetic diagnosis of Niemann-Pick disease by enabling classification of novel SMPD1 variants

Background: Niemann Pick (NP) disease is a genetically heterogeneous metabolic disorder caused by bi-allelic variants in NPC1, NPC2 or SMPD1, with initial symptoms and age at onset varying widely. The interpretation of variants in NP disease genes is challenging when these alterations have never been observed before, and when parental samples are not available. Case Presentation: We clinically, genetically, and biochemically characterized an infant with a complex presentation and a negative family history. Clinical and paraclinical observations were consistent with NP disease. Genetic screening identified two previously unreported SMPD1 missense variants, which were initially classified as variants of unknown significance. Based on strongly increased plasma levels of lysosphingomyelin-509, both variants could be re-classified as likely pathogenic, thus establishing a diagnosis of NP disease type A/B. Conclusions: A combination of genetics with biochemical approaches facilitates conclusive diagnosis of metabolic disorders including NP disease. Blood-based biomarkers are particularly promising in this respect.make italic