Context: In monocarboxylate transporter 8 (MCT8) gene deficiency, a syndrome combining thyroid and neurological abnormalities, the central nervous system has not yet been characterized by magnetic resonance spectroscopy (MR spectroscopy).

Objective:We studied whether the degree of dysmyelinization in MCT8 gene deficiency according to MRI, is coupled with abnormalities in brain metabolism.

Design: MRI and MR spectroscopy of the brain were performed twice in two MCT 8 gene deficiency patients, for the first time at age 8–10 months and for the second time at age 17–28 months. The results were compared with those obtained in controls of similar age.

Results: Compared with controls, young children with MCT8 show choline and myo-inositol level increases and N-acetyl aspartate decreases in supraventricular gray and white matter, phenomena associated with the degree of dysmyelinization according to MRI.

Conclusion: MCT8 gene deficiency results in deviant myelinization and general atrophy, which is substantiated by the MR spectroscopy findings of increased choline and myo-insitol levels and decreased N-acetyl aspartate. The observations suggest that different mutations in the MCT8 gene lead to differences in the severity of the clinical spectrum, dysmyelinization and MR spectroscopy detectable changes in brain metabolism.