A case of Hoyeraal-Hreidarsson syndrome: Delayed myelination and hypoplasia of corpus callosum are other important signs

We report the case of a 7-year old girl with Hayeraal-Hreidarsson syndrome (HHS) and review other cases of HHS. In addition to the previously describe d important signs of HHS, i.e., prenatal growth retardation, microcephaly, psychomotor retardation, progressive pancytopenia, immunological abnormalit ies, and cerebellar hypoplasia and ataxia, we consider that delayed myelina tion of cerebral white matter and hypoplastic corpus callosum should be add ed to the list of important signs. However, it is not clear whether delayed myelination of white matter in HHS indicates dysmyelination or demyelinati on, Furthermore, we suggest that immunological abnormalities of both T and B cells are one of the important signs of HHS. We consider these new import ant signs to be valuable for the diagnosis of HHS.