Definition A severe form (OMIM:300523) of X-linked psychomotor retardation combined with thyroid hormone defects–due to impaired hormone synthesis, transport and action. Affected male patients have abnormal concentrations of circulating iodothyronines, and severe neurologic deficits, including developmental delay, central hypotonia, spastic quadriplegia, dystonic movements, rotary nystagmus, and impaired gaze and hearing. Heterozygous females have a milder thyroid phenotype and no neurologic defects.
Molecular pathology Defects of SLC16A2, which encodes a widely expressed integral membrane protein which facilitates cellular importatation of thyroid hormones and plays a key role in CNS development, cause Allan-Herndon-Dudley syndrome.
Synonyms Allan-Herndon syndrome, mental retardation and muscular atrophy, monocarboxylate transporter 8 deficiency, triiodothyronine resistance