Neurodevelopmental delay as the initial presentation of thyroid hormone resistance syndrome

Thyroid hormone (TH) resistance syndrome is a genetic disorder usually caused by a defect in TH receptors. Moreover, transport and intracellular metabolism alterations have also been described. This case report presents a child with Allan–Herndon–Dudley syndrome characterized by a mutation on the X-linked monocarboxylate transporter 8 gene, a condition that affects the transport of THs across the cell membrane, leading to hypothyroidism in the central nervous system and hyperthyroidism in peripheral tissues, causing severe neurodevelopmental delay manifesting as generalized hypotonia from birth. The utility of monitoring thyroid functions, genetic testing, and triiodothyroacetic acid in the management is highlighted.