RT Journal Article SR Electronic T1 Expanding the Phenotypic Spectrum of GPI Anchoring Deficiency Due to Biallelic Variants in GPAA1 JF Neurology Genetics JO Neurol Genet FD Lippincott Williams & Wilkins SP e631 DO 10.1212/NXG.0000000000000631 VO 7 IS 6 A1 Castle, Alison M.R. A1 Salian, Smrithi A1 Bassan, Haim A1 Sofrin-Drucker, Efrat A1 Cusmai, Raffaella A1 Herman, Kristin C. A1 Heron, Delphine A1 Keren, Boris A1 Johnstone, Devon L. A1 Mears, Wendy A1 Morlot, Susanne A1 Nguyen, Thi Tuyet Mai A1 Rock, Rachel A1 Stolerman, Elliot A1 Russo, Julia A1 Burns, William Boyce A1 Jones, Julie R. A1 Serpieri, Valentina A1 Wallaschek, Hannah A1 Zanni, Ginevra A1 Dyment, David A. A1 Campeau, Philippe M. YR 2021 UL http://ng.neurology.org/content/7/6/e631.abstract AB Background and Objectives To expand the clinical knowledge of GPAA1-related glycosylphosphatidylinositol (GPI) deficiency.Methods An international case series of 7 patients with biallelic GPAA1 variants were identified. Clinical, biochemical, and neuroimaging data were collected for comparison. Where possible, GPI-anchored proteins were assessed using flow cytometry.Results Ten novel variants were identified in 7 patients. Flow cytometry samples of 3 available patients confirmed deficiency of several GPI-anchored proteins on leukocytes. Extensive phenotypic information was available for each patient. The majority experienced developmental delay, seizures, and hypotonia. Neuroimaging revealed cerebellar anomalies in the majority of the patients. Alkaline phosphatase was within the normal range in 5 individuals and low in 1 individual, as has been noted in other transamidase defects. We notably describe individuals either less affected or older than the ones published previously.Discussion Clinical features of the cases reported broaden the spectrum of the known phenotype of GPAA1-related GPI deficiency, while outlining the importance of using functional studies such as flow cytometry to aid in variant classification.AP=anchored protein; ALP=alkaline phosphatase; FLAER=fluorescein-labeled proaerolysin; GPI=glycosylphosphatidylinositol; WES=whole-exome sequencing