Primary myelofibrosis is a condition characterized by the buildup of scar tissue (fibrosis) in the bone marrow, the tissue that produces blood cells. Because of the fibrosis, the bone marrow is unable to make enough normal blood cells. The shortage of blood cells causes many of the signs and symptoms of primary myelofibrosis.\n\nInitially, most people with primary myelofibrosis have no signs or symptoms. Eventually, fibrosis can lead to a reduction in the number of red blood cells, white blood cells, and platelets. A shortage of red blood cells (anemia) often causes extreme tiredness (fatigue) or shortness of breath. A loss of white blood cells can lead to an increased number of infections, and a reduction of platelets can cause easy bleeding or bruising.\n\nBecause blood cell formation (hematopoiesis) in the bone marrow is disrupted, other organs such as the spleen or liver may begin to produce blood cells. This process, called extramedullary hematopoiesis, often leads to an enlarged spleen (splenomegaly) or an enlarged liver (hepatomegaly). People with splenomegaly may feel pain or fullness in the abdomen, especially below the ribs on the left side. Other common signs and symptoms of primary myelofibrosis include fever, night sweats, and bone pain.\n\nPrimary myelofibrosis is most commonly diagnosed in people aged 50 to 80 but can occur at any age.

The gray platelet syndrome (GPS) is a rare inherited disorder characterized by mild to moderate bleeding tendency, moderate thrombocytopenia, and a marked decrease or absence of platelet alpha-granules and of the proteins contained in alpha-granules. The platelets are enlarged, but not giant, and have a gray appearance on light microscopy of Wright-stained peripheral blood smears due to decreased granules. Many patients with gray platelet syndrome develop a stable myelofibrosis (summary by Nurden and Nurden, 2007). Cases suggesting autosomal dominant and autosomal recessive inheritance have been described, indicating that GPS is probably a genetically heterogeneous disorder with more than one molecular cause.

Ghosal hematodiaphyseal dysplasia (GHDD) is an autosomal recessive disorder characterized by increased bone density with predominant diaphyseal involvement and aregenerative corticosteroid-sensitive anemia (summary by Genevieve et al., 2008).

Platelet-type bleeding disorder-17 is an autosomal dominant disorder characterized by increased bleeding tendency due to abnormal platelet function. It is a type of 'gray platelet syndrome' because the platelets appear abnormal on light microscopy. Electron microscopy shows decreased or absent alpha-granules within platelets, and bone marrow biopsy shows increased numbers of abnormal megakaryocytes, suggesting a defect in megakaryopoiesis and platelet production. The bleeding severity is variable (summary by Monteferrario et al., 2014).

A rare chromosomal anomaly syndrome resulting from the partial duplication of the long arm of chromosome 14 that results in a predisposition to a number of adult-onset myeloproliferative neoplasms, including acute myeloid leukaemia, chronic myelomonocytic leukaemia and myeloproliferative neoplasms especially essential thrombocythemia. Progression to myelofibrosis and secondary acute myeloid leukaemia can be observed.

Thrombocytopenia-6 is an autosomal dominant hematologic disorder characterized by increased bleeding episodes due to reduced platelet count and abnormal platelet morphology resulting from defective megakaryopoiesis. Patients may also have bone abnormalities, including osteoporosis or tooth loss, as well as an increased risk for myelofibrosis (summary by Turro et al., 2016). For a general phenotypic description and a discussion of genetic heterogeneity of thrombocytopenia, see 313900.

Noonan syndrome-like disorder with loose anagen hair is characterized by facial features similar to those observed in Noonan syndrome (163950), including hypertelorism, ptosis, downslanting palpebral fissures, low-set posteriorly angulated ears, and overfolded pinnae. In addition, patients display short stature, frequently with growth hormone (GH; see 139250) deficiency; cognitive deficits; relative macrocephaly; small posterior fossa resulting in Chiari I malformation; hypernasal voice; cardiac defects, especially dysplasia of the mitral valve and septal defects; and ectodermal abnormalities, in which the most characteristic feature is the hair anomaly, including easily pluckable, sparse, thin, slow-growing hair (summary by Bertola et al., 2017). Reviews Komatsuzaki et al. (2010) reviewed the clinical manifestations of patients with Noonan syndrome, Costello syndrome (218040), and cardiofaciocutaneous syndrome (CFC; see 115150) compared to patients with mutations in the SHOC2 gene. They noted that although there is phenotypic overlap among the disorders, loose anagen/easily pluckable hair had not been reported in mutation-positive patients with Noonan, CFC, or Costello syndrome, and appeared to be a distinctive feature of SHOC2 mutation-positive patients. Genetic Heterogeneity of Noonan Syndrome-Like Disorder with Loose Anagen Hair NSLH2 (617506) is caused by mutation in the PPP1CB gene (600590) on chromosome 2p23.

X-linked immunodeficiency-98 with autoinflammation (IMD98) is characterized by onset of recurrent infections associated with lymphoproliferation and autoinflammation in the first decade of life. Mostly males are affected; carrier females may have mild symptoms. Laboratory studies show evidence of immune dysregulation, including hypogammaglobulinemia with reduced memory B cells, skewed T-cell subsets, increased levels of proinflammatory cytokines, activated T cells and monocytes, and autoimmune cytopenias, including neutropenia (Aluri et al., 2021; Fejtkova et al., 2022).