Severe Neurological Abnormalities in a Young Boy with Impaired Thyroid Hormone Sensitivity Due to a Novel Mutation in the MCT8 Gene

Rego, TGomez Lado, CCabanas Rodríguez, PSousa Santos, FBarros Angueira, FCastro-Feijóo, LBarreiro Conde, JCastro-Gago, M2023-10-062023-10-062017-04Hormones (Athens) . 2017 Apr;16(2):194-199.http://hdl.handle.net/10400.17/4712Monocarboxylate 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.engHCC ENDHumansChildMaleDevelopmental Disabilities / diagnosis*Developmental Disabilities / geneticsDyskinesias / diagnosis*Dyskinesias / geneticsIntellectual Disability / diagnosis*Intellectual Disability / geneticsMental Retardation, X-Linked / diagnosis*Mental Retardation, X-Linked / geneticsMonocarboxylic Acid Transporters / genetics*Muscle Hypotonia / diagnosis*Muscle Hypotonia / geneticsMuscular Atrophy / diagnosis*Muscular Atrophy / geneticsMutation, MissenseQuadriplegia / diagnosis*Quadriplegia / geneticsSymportersThyrotoxicosis / diagnosis*Thyrotoxicosis / geneticsSevere Neurological Abnormalities in a Young Boy with Impaired Thyroid Hormone Sensitivity Due to a Novel Mutation in the MCT8 Genejournal article10.14310/horm.2002.1733.