[MCT8-specific thyroid hormone cell transporter deficiency: a case report and review of the literature].

INTRODUCTION: MCT8 is a specific transporter for the T4 and T3 thyroid hormones that allows their entry in the brain and other organs. Mutations in MCT8 (Allan-Herndon-Dudley syndrome) lead to a severe form of X-linked psychomotor retardation, which is characterised by elevated plasma T3 and low T4.

AIM: We describe the first case diagnosed in Spain with this syndrome and review the published literature about this topic. We both review the various clinical presentations, genetic advances, differential diagnosis and therapeutic perspectives of this syndrome and propose a diagnostic algorithm for it.

CASE REPORT: A 5 year-old boy, with a clinical picture compatible with Pelizaeus-Merzbacher disease. PLP1 gene sequencing showed no abnormalities. All the genetic and metabolic studies conducted were normal. Finally, a complete study of thyroid profile revealed abnormalities that were consistent with MCT8 transporter deficiency. The sequencing of the SLC16A2 gene (MCT8) showed a mutation in exon 3 and the study made at a cellular level, has confirmed that this mutation changes the properties of the protein.

CONCLUSIONS: In the last five years, there have been many publications about this syndrome, with the identification of more than 50 families worldwide. It is important to both know and suspect this syndrome, because the diagnosis is easy, cheap and accessible (thyroid profile) and, although it has no specific treatment, early diagnosis prevents unnecessary testing and allows to offer genetic counseling to the families affected by it.