Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare disease characterized by an isolated severe hypomegakaryocytic thrombocytopenia during the first years of life that develops into bone marrow failure and pancytopenia in later childhood. The exact prevalence is unknown and since the cloning of the gene responsible for the disease, a limited number of cases have been reported in the literature. In addition, the reported incidence may be underestimated due to difficult and inconsistent diagnosis of the disease. CAMT manifests in infancy (often recognized on day 1 of life or at least within the first month) and is characterized by isolated thrombocytopenia at birth and the near absence of megakaryocytes in the bone marrow. Two types of CAMT (with or without a variety of congenital anomalies) have been identified. Abnormalities of the central nervous system (cerebral and cerebellar hypoplasia), skeletal abnormalities, cardiac defects (ventricular and atrial septal defects), and retardation of psychomotor development have occasionally been reported. Petechiae since birth and intracranial hemorrhage are the most relevant clinical manifestations. Serum levels of thrombopoietin (TPO) are highly elevated in all CAMT patients. The severe form of the disease is characterized by persistently low platelet counts and early progression to bone marrow aplasia, while a milder form presents with transient increases of platelet counts over 50x109/L during the first year of life and later development of pancytopenia. CAMT is induced by mutations of the gene coding for TPO receptor (c-MPL). The inheritance pattern is autosomal recessive. Different types of mutations have been associated with different phenotypes. Mutations predicted to result in a complete loss of function of the TPO receptor led to more severe thrombocytopenia and early onset of pancytopenia, whereas missense mutations were associated with transient increases of platelet counts during the first year of life and late or no development of pancytopenia. Diagnosis is based on the clinical and laboratory data. The initial presentation of CAMT with isolated thrombocytopenia can be easily misdiagnosed as idiopathic thrombocytopenic purpura (ITP), while the late pancytopenic phase is indistinguishable from aplastic anaemia. Fanconi's anaemia and thrombocytopenia absent radius syndrome (see these terms) should be ruled out. With supportive therapy, progression to marrow failure occurs during the first decade of life. At present, allogeneic stem cell transplantation is the only curative therapy for CAMT and is successful in approximately half of patients.
Last update: November 2007
- Pr Joan Lluís VIVES-CORRONS