Hypoprebetalipoproteinemia, acanthocytosis, retinitis pigmentosa, and pallidal degeneration (HARP syndrome).

We describe the clinical and laboratory studies of an 11-year-old girl with prominent orofacial dyskinesia, dystonia, and progressive dementia. Investigations revealed hypoprebetalipoproteinemia, acanthocytosis, atypical retinitis pigmentosa, and evidence of iron deposition in the pallidal nuclei. Electroneuromyography and skin and sural nerve biopsies were normal. The "eye-of-the-tiger" sign, used to describe the pallidal nuclei in Hallervorden-Spatz syndrome, was present on T2-weighted MRIs (GE Signa, 1.5 T). Phase-contrast microscopy of whole blood showed 80 to 90% acanthocytes whose morphology was confirmed by electron microscopy. High-resolution lipoprotein electrophoresis demonstrated an absence of the pre-beta fraction. This case differs phenotypically from the previous reports of Hallervorden-Spatz disease with acanthocytosis by the presence of prominent orofacial dyskinesia and abnormal serum lipoproteins.