Scott syndrome

Scott syndrome is a rare congenital bleeding disorder that is due to a defect in a platelet mechanism required for blood coagulation.[1]

Scott syndrome
Other names	Platelet factor X receptor deficiency
This condition is inherited in an autosomal recessive manner

Normally when a vascular injury occurs, platelets are activated and phosphatidylserine (PS) in the inner leaflet of the platelet membrane is transported to the outer leaflet of the platelet membrane, where it provides a binding site for plasma protein complexes that are involved in the conversion of prothrombin to thrombin, such as factor VIIIa-IXa (tenase) and factor Va-Xa (prothrombinase).[2]

In Scott syndrome, the mechanism for translocating PS to the platelet membrane is defective, resulting in impaired thrombin formation.[3][4][5] A similar defect in PS translocation has also been demonstrated in Scott syndrome red blood cells and Epstein-Barr virus transformed lymphocytes, suggesting that the defect in Scott syndrome reflects a mutation in a stem cell that affects multiple hematological lineages.

The basis for the defect in PS translocation is, at present, unknown. A candidate protein, scramblase,[6] that may be involved in this process appears to be normal in Scott syndrome platelets.[7] Other possible defects in PS translocation, reported in some patients, require further study.[8] The initially reported patient with Scott Syndrome has been found to have a mutation at a splice-acceptor site of the gene encoding transmembrane protein 16F (TMEM16F).[9] At present, the only treatment for episodes of bleeding is the transfusion of normal platelets.