Elevated Red Cell Reduced Glutathione Is a Novel Biomarker of Diamond-Blackfan Anemia

Diamond-Blackfan anemia (DBA) is a rare congenital red cell aplasia characterized by congenital anomalies and predisposition to cancer. Recent observation disclosed that heterogeneous mutations in ribosomal protein (RP) genes are present in approximately 50% of patients, suggesting that diagnosis should be made by clinical phenotypes such as age, hematological findings or positive family history. Although elevated activity of red cell adenosine deaminase (eADA) has been utilized as a useful biomarker for differential diagnosis of DBA, approximately 20% of DBA patients are eADA-negative. Recent observations suggested that ribosomal haploinsufficiency increases oxidative stress, leading to p53 gene activation and premature death of erythroid cells. We hypothesized that reduced glutathione (GSH), an essential antioxidant of erythroid cells, might be upregulated in red cells of DBA subjects. In order to test this hypothesis, we examined red cell GSH as well as eADA of 22 patients in 18 DBA families, in whom we had identified gene mutations in RPS19, RPL5, RPL11, RPS10, RPS17 or RPS35a. All except one DBA patients showed elevated GSH (>88.6 mg/dl RBC, M+SD), whereas 17 out of 22 patients exhibited elevated eADA (>2.31 IU/g Hb, M+3SD). We also examined 14 unaffected members of the DBA families, with 1 out of 14 subjects showing elevated GSH and none showing elevated eADA. We performed linear discriminant analysis between DBA and non-DBA subjects with both eADA and GSH using the Support Vector Machine (SVM) from 36 subjects, and successfully obtained a formula to discriminate DBA from unaffected subjects: 0.937*eADA+0.0702*GSH-7.9044 >0. By using this formula, all DBA examined can be diagnosed and unaffected family members can be excluded. Since approximately 50% of clinically diagnosed DBA cases have no causative RP gene mutations, the combined assessment of eADA and GSH might be quite useful for biochemical diagnosis of DBA.