Hoyeraal-Hreidarsson Syndrome (HHS) is a severe X-linked multi-system disorder that is associated with microcephaly,
delays in intrauterine growth, intellectual disability, spastic paresis, ataxia, and
immunodeficiency. Other clinical manifestations include hyperpigmentation; nail dystrophy,
oral and premalignant leukoplakia affecting oral and gastrointestinal mucosa. Affected
individuals have an unusually small and underdeveloped cerebellum, which is the part
of the brain that coordinates movement. People with HHS usually develop early onset
bone marrow failure, immunodeficiency and pancytopenia. HHS is caused by mutations
in the DKC1 gene.
DIAGNOSTIC TESTING, PHYSICAL FINDINGS, AND ICD-9-CM CODING
Diagnostic testing: Neuroimaging reports showing cerebellar hypoplasia/atrophy, small brainstem, thin
corpus callosum and cerebral calcifications. Genetic testing for the DKC1 gene confirms the clinical diagnosis.
Physical findings: Individuals with HHS are at risk for progressive bone marrow failure, myelodysplastic
syndrome or acute leukemia, solid tumors of the head/neck, pulmonary fibrosis, and
abnormal pigmentation changes to the upper chest/neck, eye abnormalities, dental abnormalities,
developmental delay, cerebellar hypoplasia, bilateral exudative retinopathy, and intracranial
ICD-9: 284 (Constitutional aplastic anemia); 287.33
* Adjudicators may, at their discretion, use the Medical Evidence of Record or Listings
suggested to evaluate the claim. However, the decision to allow or deny the claim
rests with the adjudicator.