Absent α-granules in platelets from VPS16B null patients. Thin-section transmission electron micrographs of representative platelets from control neonatal and VPS16B null neonatal blood. Magnification is ×30 000 and scale bar represents 500 nm. (A) Control platelets contain multiple α-granules (white arrowheads), which are absent in VPS16B null platelets (B). The dark-staining structures seen in the VPS16B null platelet (B) contain distinct internal membranes that probably represent mitochondria.