With genetic testing available, PKAN has transpired to be the diagnosis in the two cases that had entered the literature under the “HARP” acronym (hypoprebetalipoproteinemia, acanthocytosis, retinitis pigmentosa, pallidal degeneration) [26, 27, 28, 29], in spite of general doubts as to the utility and even meaning of “hypoprebetalipoproteinemia” [30]. This evidence concerns the gene PANK2 and retinitis pigmentosa.