GTR Home > Conditions/Phenotypes > Allan-Herndon-Dudley syndrome

Disease characteristics

Excerpted from the GeneReview: MCT8-Specific Thyroid Hormone Cell-Membrane Transporter Deficiency
MCT8-specific thyroid hormone cell-membrane transporter deficiency is characterized by severe cognitive deficiency, infantile hypotonia, diminished muscle mass and generalized muscle weakness, progressive spastic quadriplegia, joint contractures, and dystonic and/or athetoid movement with characteristic paroxysms or kinesigenic dyskinesias. Seizures occur in about 25% of cases. Most affected males never sit or walk independently or lose these abilities over time; most never speak or have severely dysarthric speech. Brain MRI obtained in the first few years of life shows transient delayed myelination, which improves by age four years. Although psychomotor findings observed in affected males do not occur in heterozygous females, the latter often have thyroid test abnormalities intermediate between affected and normal individuals.

Available tests

23 tests are in the database for this condition. Compare labs offering these tests.

Check Associated genes for additional relevant tests.

Associated genes

  • Also known as: RP11-449M9.1, AHDS, DXS128, DXS128E, MCT 7, MCT 8, MCT7, MCT8, MRX22, XPCT, SLC16A2
    Summary: solute carrier family 16, member 2 (thyroid hormone transporter)

Clinical features

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  • Irritability
  • Babinski sign
  • Intellectual disability, severe
  • Hyperreflexia
  • Cerebral calcification
  • Inability to walk
  • Neonatal hypotonia
  • Narrow face
  • Narrow forehead
  • Gait disturbance
  • Dysarthria
  • Type I diabetes mellitus
  • Involuntary writhing movements
  • Prominent antihelix
  • Abnormal conjugate eye movement
  • Microcephaly
  • Intellectual disability, progressive
  • Spastic paraplegia
  • Hallux valgus
  • Cognitive impairment
  • Open mouth
  • Amyotrophy
  • Macrotia
  • Proptosis
  • Incoordination
  • Single transverse palmar crease
  • Feeding difficulties in infancy
  • Hypothyroidism
  • Abnormality of the neck
  • Ptosis
  • Upslanted palpebral fissure
  • Pectus excavatum
  • Ataxia
  • Flexion contracture
  • Limitation of joint mobility
  • Abnormality of the rib cage
  • Rotary nystagmus
  • Pes planus
  • Neurological speech impairment
  • Clonus
  • Delayed CNS myelination
  • Drooling
  • Leukodystrophy
  • Spastic tetraplegia
  • Scoliosis
  • Thyroid-stimulating hormone excess
  • Generalized amyotrophy
  • Cheekbone underdevelopment
  • Stahl ear
  • Camptodactyly of finger
  • Severe global developmental delay
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