HSPA9 and lactic acidosis: Using primary fibroblasts containing bi-allelic mutations (p.Tyr565His and p.Glu733Lys; NM_004793.3) within the LONP1 ATPase domain associated with congenital lactic acidosis, muscle weakness, and multiple mitochondrial OXPHOS deficiencies29, we found substantially reduced solubility of mtHSP70, DNAJA3 and OXA1L (Fig. 4d).