Thyroid Hormone Transporter Defect: Allan Herndon Dudley Syndrome, Masquerading as Dyskinetic Cerebral Palsy.

Allan Herndon Dudley syndrome (AHDS) is a rare X-linked recessive disorder due to mutation in the SLC16A2 gene, which encodes a thyroid hormone (TH) transporter that facilitates the movement of TH across the neurons. Mutation in this gene leads to a lack of T3 and T4 entry in the brain, which causes central hypothyroidism and dysthyroidism in the peripheral tissue. We report a child, a 21-month-old boy, who presented with developmental delay and stiffness. The child had facial dysmorphism with dystonia. MRI of the brain was normal. Thyroid profile showed low free T4, and normal TSH but high free T3. Hence, AHDS was suspected and was confirmed by targeted next-generation testing and Sanger sequencing.