Severe neurological abnormalities in a young boy with impaired thyroid hormone sensitivity due to a novel mutation in the MCT8 gene

• Published in: Hormones (Athens, Greece) Vol. 16; no. 2; pp. 194 - 199
• Main Authors: Rego, Teresa, Lado, Carmen Gomez, Rodríguez, Paloma Cabanas, Santos, Francisco Sousa, Angueira, Francisco Barros, Castro-Feijóo, Lidia, Conde, Jesús Barreiro, Castro-Gago, Manuel
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01-04-2017
• Subjects: Case Report; Child; Developmental Disabilities - diagnosis; Developmental Disabilities - genetics; Dyskinesias - diagnosis; Dyskinesias - genetics; Endocrinology; Humans; Intellectual Disability - diagnosis; Intellectual Disability - genetics; Male; Medicine; Medicine & Public Health; Mental Retardation, X-Linked - diagnosis; Mental Retardation, X-Linked - genetics; Metabolic Diseases; Monocarboxylic Acid Transporters - genetics; Muscle Hypotonia - diagnosis; Muscle Hypotonia - genetics; Muscular Atrophy - diagnosis; Muscular Atrophy - genetics; Mutation, Missense; Quadriplegia - diagnosis; Quadriplegia - genetics; Thyrotoxicosis - diagnosis; Thyrotoxicosis - genetics; Allan-Herndon-Dudley syndrome; Thyroid dysfunction; Psychomotor retardation; Low T3; Thyroid hormone transporter; Severe neurological phenotype; MCT8; Impaired thyroid hormone sensitivity
• ISSN: 1109-3099; 2520-8721
• DOI: 10.14310/horm.2002.1733

Monocarboxylate transporter 8 (MCT8) is an active and specific thyroid hormone transporter into neurons.
MCT8
mutations cause an X-linked condition known as Allan-Herndon-Dudley syndrome and are characterized by impaired psychomotor development and typical abnormal thyroid function. We describe a 10-year-old boy with severe cognitive disability, axial hypotonia, spastic quadriplegia and sporadic dyskinetic episodes. He initially presented with thyroid dysfunction (high FT3, low rT3, low FT4 and normal TSH) and generalized retardation of the cerebral and cerebellar myelination in brain magnetic resonance imaging. The clinical and laboratory findings led to sequencing of the
SLC16A2/MCT8
gene, which identified a novel missense mutation in exon 5. The study of peripheral markers of thyroid function suggests a paradoxical state of thyrotoxicosis in some peripheral tissues. Our patient had a typical clinical presentation at birth but because of the rarity of his disease his diagnosis was not made until the age of 7. The delay can also be explained by the omission of the free T3 assay in the first thyroid evaluation performed. This case therefore highlights the possible benefit of including the T3 assay in the study of patients with severe psychomotor disability of unknown etiology, thus eliminating extra costs for unnecessary complementary diagnostic tests.