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.

Hermansky-Pudlak syndrome (HPS) is characterized by oculocutaneous albinism, a bleeding diathesis, and, in some individuals, pulmonary fibrosis, granulomatous colitis, or immunodeficiency. Ocular findings include reduced iris pigment with iris transillumination, reduced retinal pigment, foveal hypoplasia with significant reduction in visual acuity (usually in the range of 20/50 to 20/400), nystagmus, and increased crossing of the optic nerve fibers. Hair color ranges from white to brown; skin color ranges from white to olive and is usually a shade lighter than that of other family members. The bleeding diathesis can result in variable bruising, epistaxis, gingival bleeding, postpartum hemorrhage, colonic bleeding, and prolonged bleeding with menses or after tooth extraction, circumcision, and other surgeries. Pulmonary fibrosis, a restrictive lung disease, typically causes symptoms in the early thirties 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.