Congenital storage pool deficiency: dense granules

• Normal platelet dense (d) granules store ADP, ATP, calcium, pyrophosphate, and serotonin, and release these during activation.
• Hermansky-Pudlak and Chediak-Higashi syndromes are rare autosomal recessive disorders with oculocutaneous albinism.
• Wiskott-Aldrich syndrome, an X-linked recessive disorder, is characterized by severe eczema.
• All three have reduced dense granule distribution (diagnosed by electron microscopy) and moderate thrombocytopenia.
• Dense granule deficiency in non-albinos may be caused by an autosomal dominant inability to package the normal contents despite producing normal granules. Platelet counts are normal. 
  

Congenital storage pool deficiency: a  granules

• The a granules store coagulation factors, platelet-derived growth factor (PDGF) and platelet factor 4. They provide the granular appearance of platelets by light microscopy.
• Gray platelet syndrome is the absence of a  granules; the platelets are large and gray. Patients experience thrombocytopenia and moderate life-long bleeding.

Acquired storage pool deficiency: MPD or MDS

• Platelets in myeloproliferative disorders and myelodysplastic syndromes have reduced  a and d granules, abnormal membranes, and vary in size and count.
• Patients may have mild to moderate bleeding, although thrombosis is also a risk.
• Platelet aggregometry may be used to predict clinical bleeding.

Platelet receptor defects

Following is a table of platelet membrane receptor defects that may associate with mucocutaneous bleeding. These may be detected using platelet aggregometry.