Program Operations Manual System (POMS)
TN 30 (08-20)
DI 23022.925 Allan-Herndon-Dudley Syndrome
COMPASSIONATE ALLOWANCES INFORMATION
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ALLAN-HERNDON-DUDLEY SYNDROME
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ALTERNATE NAMES
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Allan-Herndon Syndrome; X-linked Intellectual Deficit with Hypotonia; Monocarboxylate
Transporter 8 Deficiency; MCT8 Deficiency; MCT8 Specific Thyroid Hormone Cell Transporter
Deficiency; MCT8 SLC16A2AHDS; Triidothyronine Resistence; T3 Resistence; Intellectual
Disability and Muscular Atrophy; X-linked Intellectual Disability with Hypotonia
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DESCRIPTION
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Allan-Herndon-Dudley Syndrome (AHDS) is a rare inherited disorder of brain development that causes moderate to severe
intellectual disability and problems with movement. Some children with AHDS have difficulty
with communication and speech. Mutations in the SLC16A2 gene (also known as MCT8)
cause AHDS. The SLC16A2 gene provides instruction for making a protein that transports
thyroid hormone triiodothyronine (T3) into nerve cells during development. Because
of the mutation, normal brain development is disrupted and T3 accumulates in the blood,
causing toxicity in some organs and exacerbations of the symptoms of AHDS. This condition
occurs exclusively in males.
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DIAGNOSTIC TESTING, PHYSICAL FINDINGS, AND ICD-9-CM/ICD-10-CM
CODING
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Diagnostic
testing: The diagnosis is established by a combination of clinical examination and molecular
genetic testing for mutations in the SLC16A2 gene, elevated T3, and decreased T4 in
the blood.
Physical findings: The physical findings of AHDS may include:
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Abnormal folding of the ears;
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Abnormal muscle tone (initially hypotonia, later evolving into spasticity);
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Underdevelopment of muscles (muscle hypoplasia);
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ICD-9: 359
ICD-10:
G72.89
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PROGRESSION
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Children with AHDS usually appear normal at birth with signs of the disease occurring
shortly after birth with poor muscle tone, inability to control head movements, and
physical and developmental delays. Progressively worsening muscle weakness, stiffness,
exaggerated reflexes, joint deformities, and involuntary movements of the limbs eventually
leads to wheel chair dependency by early adulthood. Some children may have delays
in language development.
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TREATMENT
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Presently, there is no standardized treatment for AHDS. Treatment is symptom specific
and supportive.
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SUGGESTED PROGRAMMATIC ASSESSMENT*
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Suggested MER for Evaluation:
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Clinical history and examination that describes the progression of neurological and
cognitive decline from the claimant’s medical source(s);
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Genetic testing for mutations in the SLC16A2 (or MCT8) gene; and
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Laboratory blood testing with elevations in free T3 and decreased free T4.
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Suggested Listings for Evaluation:
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DETERMINATION |
LISTING |
REMARKS |
Meets
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111.17 |
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Equals
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111.07 B |
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* Adjudicators may, at their discretion, use the Medical Evidence of Record or the
listings suggested to evaluate the claim. However, the decision to allow or deny the
claim rests with the adjudicator.
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