Thrombocythaemia 3
Autosomal dominant · Rare; reported in a small number of families.
Caused by an inherited change in JAK2, which makes a signalling protein that controls blood cell production. The reported changes lie in the parts of the protein that control its activity and make it more active, which raises platelet production. The first described, JAK2 R564Q, was found in a family with dominantly inherited thrombocythaemia.
Signs and symptoms
A raised platelet count, which in some families is present from birth. In laboratory studies these inherited changes have a milder effect than the common acquired JAK2 V617F change, but in one reported series many people had symptoms comparable to those with V617F. Some affected people have also developed blood cancers, including myeloproliferative neoplasms.
What a diagnosis changes
Follow-up with a haematologist, including monitoring of blood counts, since blood cancers have occurred in some affected families. Evidence is limited, and for children there are no agreed guidelines. Because it is inherited in an autosomal dominant way, each child of an affected parent has a 1 in 2 chance of inheriting the change, and testing relatives can show who else carries it.
Genes analysed
Also known as
familial thrombocytosis caused by mutation in JAK2; JAK2 familial thrombocytosis; THCYT3; thrombocythemia 3, autosomal dominant, somatic mutation; thrombocythemia type 3
