Defect in Dimethylglycine Dehydrogenase, a New Inborn Error of Metabolism: NMR Spectroscopy Study

A38-year-old man presented with a history of fish odor (since age 5) and unusual muscle fatigue with increased serum creatine kinase. Our aim was to identify the metabolic error in this new condition. We used 1H NMR spectroscopy to study serum and urine from the patient. The concentration of N, N-dimethylglycine (DMG) was increased approximately 100-fold in the serum and approximately 20-fold in the urine. The presence of DMG as a storage product was confirmed by use of 13C NMR spectroscopy and gas chromatography-mass spectrometry. The high concentration of DMG was caused by a deficiency of the enzyme dimethylglycine dehydrogenase (DMGDH). A homozygous missense mutation was found in the DMGDH gene of the patient. DMGDH deficiency must be added to the differential diagnosis of patients complaining of a fish odor. This deficiency is the first inborn error of metabolism discovered by use of in vitro 1H NMR spectroscopy of body fluids.