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A novel syndrome combining thyroid and neurological abnormalities is associated with mutations in a monocarboxylate transporter gene.

Thyroid hormones are iodothyronines that control growth and development, as well as brain function and metabolism. Although thyroid hormone deficiency can be caused by defects of hormone synthesis and action, it has not been linked to a defect in cellular hormone transport. In fact, the physiological role of the several classes of membrane transporters remains unknown. We now report, for the first time, mutations in the monocarboxylate transporter 8 (MCT8) gene, located on the X chromosome, that encodes a 613-amino acid protein with 12 predicted transmembrane domains. The propositi of two unrelated families are males with abnormal relative concentrations of three circulating iodothyronines, as well as neurological abnormalities, including global developmental delay, central hypotonia, spastic quadriplegia, dystonic movements, rotary nystagmus, and impaired gaze and hearing. Heterozygous females had a milder thyroid phenotype and no neurological defects. These findings establish the physiological importance of MCT8 as a thyroid hormone transporter.

Pubmed ID: 14661163


  • Dumitrescu AM
  • Liao XH
  • Best TB
  • Brockmann K
  • Refetoff S


American journal of human genetics

Publication Data

January 23, 2004

Associated Grants

  • Agency: NIDDK NIH HHS, Id: DK17050
  • Agency: NCRR NIH HHS, Id: RR00055

Mesh Terms

  • Base Sequence
  • Brain
  • Child
  • Child, Preschool
  • Congenital Hypothyroidism
  • Electroencephalography
  • Female
  • Humans
  • Hypothyroidism
  • Male
  • Monocarboxylic Acid Transporters
  • Mutation
  • Nystagmus, Congenital
  • Pedigree
  • Quadriplegia
  • Thyroid Function Tests