Allan-Herndon-Dudley Syndrome

MCT8 - Specific Thyroid Hormone Cell Transporter Deficiency

Gene: SLC16A2 (commonly called MCT8)

Protein: monocarboxylate transporter 8

Clinical Characteristics

  • Severe intellectual disability
  • Hypotonia
  • High T3 and low reverse T3 without clinical signs of hypothyroidism
  • Low muscle mass
  • Generalized muscle weakness
  • Progressive spastic quadriplegia
  • Dystonic or athetoid movements
  • Paroxysmal kinesigenic dyskinesias
  • Joint contractures
  • Dysarthric or absent speech
  • Delayed myelination
  • Seizures in approximately 25% of cases

Inheritance pattern: X-linked

What Can Be Learned From This Test

Testing is performed by sequencing the entire coding region of the MCT8 gene. This will detect point mutations, small deletions and small insertions. It will not detect a partial or whole gene deletion or duplication.

MCT8 is the only gene known to be associated with Allan-Herndon-Dudley syndrome. Differential diagnoses include Pelizaeus-Merzbacher disease and MECP2 duplication syndrome, both of which are available for clinical testing in our lab. This test will only detect mutations in MCT8.

Sample Requirements

Draw 2ml–4ml of blood in EDTA/purple-top tube (minimum of 1ml–2ml for infants).

Turnaround time: 10-14 business days

CPT Codes and Cost

Full Gene Sequencing

  • Code: 81405
  • Cost: $800

Known Variant Testing

  • Code: 81479
  • Cost: $225

Additional Information