Diagnostic and therapeutic challenges in the Allan-Herndon-Dudley Syndrome

Thyroid hormone (TH) is important for normal brain development. The TH transporter protein monocarboxylate transporter 8 (MCT8) is crucial to maintain adequate TH levels in the brain during development and throughout life. Mutations in MCT8 result in the Allan-Herndon-Dudley syndrome (AHDS), which is characterized by a severe delay in neurocognitive development, combined with abnormal serum thyroid function tests (TFTs). The combination of an increased (F)T3 and decreased (F)T4 and rT3 serum levels are characteristic for the presence of AHDS in male patients with moderate to severe delay in neurocognitive development. Here, we provide an overview of current insights, challenges and pitfalls in the diagnosis and management of patients with AHDS.