MedGen

Congenital amegakaryocytic thrombocytopenia-2 (CAMT2) is an autosomal recessive disorder characterized by thrombocytopenia with progression to pancytopenia, aplastic anemia, and bone marrow failure. Serum THPO is decreased or inappropriately normal, and bone marrow is hypocellular with decreased or absent megakaryocytes. Most patients present in infancy or early childhood and have a severe disease course, whereas some have later onset and milder symptoms. Bone marrow transplant is ineffective because the defect is extrinsic to hematopoietic cells. Treatment with THPO receptor (MPL; 159530) agonists results in clinical improvement and restoration of trilineage hematopoiesis (Dasouki et al., 2013; Seo et al., 2017). For a discussion of genetic heterogeneity of CAMT, see CAMT1 (604498). [from OMIM]

Thrombocytopenia-9 (THC9) is an autosomal dominant condition characterized by low platelet counts in the absence of significant bleeding tendency. Some individuals may have mild mucocutaneous bleeding, whereas others do not show bleeding and thrombocytopenia may be an incidental finding. Platelets may show normal function and morphology or be slightly enlarged with platelet anisotropy (Noris et al., 2018; Cornish et al., 2020). For a discussion of genetic heterogeneity of thrombocytopenia, see 313900. [from OMIM]

Thrombocythemia, or thrombocytosis, is a myeloproliferative disorder characterized by excessive platelet production resulting in increased numbers of circulating platelets. Thrombocythemia can be associated with thrombotic or hemorrhagic episodes and occasional leukemic transformation (summary by Wiestner et al., 1998). Genetic Heterogeneity of Thrombocythemia THCYT2 (601977) is caused by germline or somatic mutation in the THPO receptor gene (MPL; 159530) on chromosome 1p34, and THCYT3 (614521) is caused by germline or somatic mutation in the JAK2 gene (147796) on chromosome 9p. Somatic mutations in the TET2 (612839), ASXL1 (612990), SH2B3 (605093), and SF3B1 (605590) genes have also been found in cases of essential thrombocythemia. Somatic mutation in the CALR gene (109091) occurs in approximately 70% of essential thrombocythemia patients who lack JAK2 and MPL mutations (Klampfl et al., 2013; Nangalia et al., 2013). [from OMIM]