In 1944, William Allan, Nash Herndon, and Florence Dudley reported a large North American pedigree spanning six generations with 24 affected males characterized by a distinct combination of dysmorphic features, intellectual disability, and associated neurological findings.7 Further familial male cases with similar clinical features and additional characteristic thyroid hormone abnormalities were subsequently reported,8–14 resulting in the recognition of Allan-Herndon-Dudley syndrome (AHDS; OMIM 300523) as a distinct X-linked intellectual disability syndrome. Here, TG is linked to Allan-Herndon-Dudley syndrome.