RUNX1 familial platelet disorder with associated myeloid malignancies (RUNX1-FPDMM) is characterized by prolonged bleeding and/or easy bruising and an increased risk of developing a hematologic malignancy. RUNX1-FPDMM is characterized by thrombocytopenia with normal platelet size; bleeding is often greater than expected due to qualitative platelet dysfunction. Myeloid malignancies are the most common, including acute myelogenous leukemia and myelodysplastic syndrome. T- and B-cell acute lymphoblastic leukemias and lymphomas have also been reported, as well as skin manifestations (e.g., eczema, psoriasis).

Susceptibility to platelet-type bleeding disorder-13 (BDPLT13) is due to a defective thromboxane A2 receptor on platelets. The susceptibility is inherited in an autosomal dominant pattern, but clinical features, including mild mucocutaneous bleeding, occur only in the presence of a 'second hit' affecting platelet function; this second hit may be either in the TBXA2R gene or in another gene affecting the coagulation cascade (summary by Mumford et al., 2010).

Hermansky-Pudlak syndrome (HPS) is characterized by oculocutaneous albinism, a bleeding diathesis, and, in some individuals, pulmonary fibrosis, granulomatous colitis, and/or immunodeficiency. Ocular findings include nystagmus, reduced iris pigment, reduced retinal pigment, foveal hypoplasia with significant reduction in visual acuity (usually in the range of 20/50 to 20/400), and strabismus in many individuals. Hair color ranges from white to brown; skin color ranges from white to olive and is usually at least a shade lighter than that of other family members. The bleeding diathesis can result in variable degrees of bruising, epistaxis, gingival bleeding, postpartum hemorrhage, colonic bleeding, and prolonged bleeding with menses or after tooth extraction, circumcision, and/or other surgeries. Pulmonary fibrosis, colitis, and/or neutropenia have been reported in individuals with pathogenic variants in some HPS-related genes. Pulmonary fibrosis, a restrictive lung disease, typically causes symptoms in the early 30s and can progress to death within a decade. Granulomatous colitis is severe in about 15% of affected individuals. Neutropenia and/or immune defects occur primarily in individuals with pathogenic variants in AP3B1 and AP3D1.

Platelet-type bleeding disorder-22 (BDPLT22) is an autosomal recessive bleeding disorder resulting from impaired platelet aggregation due to intracellular signaling defects. Patients present in the first decade with spontaneous subcutaneous bleeding and excessive bleeding after minor injuries. Platelet counts are usually normal, although platelets show abnormal morphology (summary by Berrou et al., 2018).

Thrombocytopenia-7 (THC7) is an autosomal dominant disorder characterized by reduced peripheral platelet count. The expression and severity of the disorder is highly variable: some patients have no bleeding symptoms, whereas other have recurrent petechiae, epistaxis, or more severe bleeding episodes. A common finding is decreased alpha-granules in the platelets. There are variable findings on light and electron microscopic analysis: some patients have normal platelet morphology, whereas others show abnormal platelet morphology with cytoskeletal defects. Flow cytometric studies may show reduced expression of platelet membrane glycoproteins and activation markers (summary by Lentaigne et al., 2019 and Leinoe et al., 2021). For a general phenotypic description and a discussion of genetic heterogeneity of thrombocytopenia, see 313900.

Platelet-type bleeding disorder-24 (BDPLT24) is an autosomal dominant form of congenital macrothrombocytopenia associated with platelet anisocytosis. It is a disorder of platelet production. Affected individuals may have no or only mildly increased bleeding tendency. In vitro studies show mild platelet functional abnormalities (summary by Kunishima et al., 2011 and Nurden et al., 2011). For a discussion of genetic heterogeneity of Glanzmann thrombasthenia-like with macrothrombocytopenia, see 187800.