Two Japanese Families with Pigmented Paravenous Retinochoroidal Atrophy and HK1 Mutation: A Case Report

Hexokinase 1 (HK1) gene is the cause of autosomal dominant retinitis pigmentosa (RP) 79. To date, only E874K mutation has been reported as the causative mutation in patients with nonsyndromic RP. As a Caucasian RP case with a pathological variant of HK1 exhibiting pigmented paravenous retinochoroidal atrophy (PPRCA) phenotype was recently reported, we reviewed RP79 cases in our Japanese RP cohort. Consequently, 2 Japanese patients, who were diagnosed with RP79 by genetic tests in our RP cohort, were included in this study. Patient 1 was a 60-year-old woman. Fundus examination revealed symmetrical donut-shaped retinal degeneration, with pigment deposition avoiding the macula. Moreover, degeneration extended in a peripheral direction along the vessels like a starfish, and degeneration was observed around the veins and arteries. Patient 2 was a 75-year-old man. Fundus examination revealed symmetric macula-avoiding donut-shaped retinal degeneration, with paravenous protruding degeneration along the blood vessels like in case 1. Both Japanese cases, which belonged to two separate families, had the same HK1 pathogenic mutation, with a phenotype of PPRCA. Furthermore, atrophy along retinal arteries was noted. Reviewing previous nonsyndromic RP79 cases revealed symptoms that are believed to be those of PPRCA. Ultra-widefield fundus imaging, especially ultra-widefield fundus autofluorescence, has been useful in detecting PPRCA. If these devices become widely available, more cases may be discovered in the future because PPRCA can be used as a clue to suspect RP79, and Sanger sequencing may be used to identify pathogenic mutations in HK1 at a lower cost and more easily than using whole-exome sequencing.