Thrombopoietin (TPO), produced mainly in the liver, is a major regulator of platelet production. Serum TPO levels are generally increased in thrombocytopenia. We report a case of a 12-year-old boy with chronic severe thrombocytopenia, achondroplasia and nephritis. Severe chronic thrombocytopenia was found at 9 months of age. It was resistant to any treatment. Studies on megakaryocytic colonies in vitro revealed that the marrow cells responded well to TPO and no plasma inhibitor was found. Although hepatic function test results were normal, serum TPO levels in the patient (0.94 fmol/ml) were consistent with those in age-matched children (0.49 1.75 fmol/ml). Chronic thrombocytopenia requires individual evaluation before clinical trials with TPO.
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