NBEAL2 is mutated in gray platelet syndrome and is required for biogenesis of platelet α-granules

Abstract

Gray platelet syndrome (GPS) is an autosomal recessive bleeding disorder that is characterized by large platelets that lack α-granules. Here we show that mutations in NBEAL2 (neurobeachin-like 2), which encodes a BEACH/ARM/WD40 domain protein, cause GPS and that megakaryocytes and platelets from individuals with GPS express a unique combination of NBEAL2 transcripts. Proteomic analysis of sucrose-gradient subcellular fractions of platelets indicated that NBEAL2 localizes to the dense tubular system (endoplasmic reticulum) in platelets.

Figure 1. Cellular studies of gray platelet syndrome

(a) Light microscopy of a peripheral blood smear of the patient from family GPS-14 showing pale gray platelets (arrows), some larger than normal. (b) Normal, darkly stained platelets (arrows). (c) Transmission electron microscopy of thin sections of a platelet from GPS-13 showing absence of α-granules and abundant channels of the open canalicular system (OCS). DTS: Dense tubule system; DB: Dense body; M: Mitochondrion. (d) Normal platelet with α-granules (AG). (e) Reticulin staining of bone marrow of the patient from family GPS-4 displaying myelofibrosis (black strands). (f) Normal bone marrow without fibrosis. Scale bar indicates 10 μm (a, b) and 50 μm (e,f), (magnification x200) (g) Schematic representation of NBEAL2 gene (ENSG00000160796) with mutations indicated. The NBEAL2-001 isoform (ENST00000450053) is depicted with its BEACH, WD40 and ARM-type fold domains. Small green bars, labeled A and B, represent two NBEAL2 peptide fragments identified by mass spectrometry. A: WGSPTSLEGELGAVAIFHEALQATALR; B: AFFAEVVSDGVPLVLALVPHR.