Thus, we explored the changes in mRNA levels for the mitochondrial fusion protein genes, OPA1 (Opa1), MFN1 (Mitofusin-1), and MFN2 (Mitofusin-2), and the mitochondrial fission protein genes, MIEF1 (Mid51), MIEF2 (Mid49), FIS1 (Fis1), DNM1L (Drp1), and MFF (Mff), in HD fibroblasts. The gene discussed is FIS1; the disease is Huntington disease.