Real-world tiratricol treatment outcomes and the importance of early detection and multidisciplinary teams in MCT8 deficiency: A case report

Monocarboxylate transporter 8 (MCT8) deficiency, also known as Allan–Herndon–Dudley syndrome, is a rare genetic disorder affecting thyroid hormone transport. It is characterised by severely debilitating neurodevelopmental and endocrinological impairments, further complicated by numerous diagnostic challenges. Here, we describe the clinical journey of a male infant from birth to MCT8 deficiency diagnosis at 23 months of age and 20 months of follow-up post diagnosis. The patient presented with hypotonia, abnormal thyroid hormone levels, epilepsy and failure to gain weight. A diagnosis of MCT8 deficiency was confirmed upon identifying a pathogenic variant in the SLC16A2 gene, which encodes the MCT8 protein. The patient was initiated on 350 μg daily of tiratricol, escalated to 350 μg twice daily, and following intolerance during further escalation, the dose was maintained at 350 μg twice daily. With 11 months of treatment follow-up, the patient has shown promising signs of thyroid hormone normalization and improved weight gain. This case highlights the importance of early recognition and a well-coordinated multidisciplinary team spanning numerous specialisms to optimise outcomes for patients with MCT8 deficiency, while providing real-world data on the effects of tiratricol treatment. • At three months of age, a male patient rapidly developed hypotonia. • He exhibited abnormal thyroid levels, poor weight gain and abnormal neurodevelopmental findings. • MCT8 deficiency was diagnosed upon the discovery of a pathogenic SLC16A2 variant. • Tiratricol treatment enabled weight gain and partial thyroid hormone normalization.