Gray platelet syndrome (GPS) is a predominantly recessive platelet disorder that 
is characterized by mild thrombocytopenia with large platelets and a paucity of 
α-granules; these abnormalities cause mostly moderate but in rare cases severe 
bleeding. We sequenced the exomes of four unrelated individuals and identified 
NBEAL2 as the causative gene; it has no previously known function but is a 
member of a gene family that is involved in granule development. Silencing of 
nbeal2 in zebrafish abrogated thrombocyte formation.