Shaibani et al1 describe a patient with the phenotype of mitochondrial neurogastrointestinal encephalopathy (MNGIE) with a plasma thymidine concentration within the reference range. However, we believe their assertion that the reference plasma thymidine concentration is less than 150 mmol/L is incorrect; the accepted reference concentration is nearer to less than 0.05 μmol/L. The thymidine concentration of 100 mmol/L in the patient described, therefore, is markedly elevated. This is important because a high concentration of thymidine is thought to be central to the pathogenesis of MNGIE and, consequently, the aim of endeavors to treat MNGIE (principally bone marrow transplant and enzyme replacement) has been to achieve sustained lowering of plasma thymidine.2- 4 The occurrence of MNGIE in the absence of elevated thymidine would represent an important challenge to the validity of this approach; therefore, we would welcome clarification by Shaibani et al.
Moran NF, Baine M, Bax BE. Mitochondrial Neurogastrointestinal Encephalopathy Without Elevated Thymidine Levels. Arch Neurol. 2010;67(5):644-645. doi:10.1001/archneurol.2010.73