P.17.15 Life-threatening lactic acidosis occurring in adults with rare mutations of mtDNA: About three cases

To report three observations of life-threatening lactic acidosis occurring in adults with rare mutations of mtDNA. Acute metabolic crisis are often encountered in childhood-onset mitochondrial diseases (MD), whereas adults generally present with progressive neurological or muscle involvement. Investigations included blood analysis, EMG, and muscle biopsy for histoenzymological and respiratory chain analysis. Mitochondrial DNA analysis was performed in muscle, blood, buccal cells, and urine. Patients were one woman and two men, aged 27, 32 and 32 years. They presented with slowly progressive muscle weakness and fatigability, compatible with a normal life, several years before the acute metabolic crisis. Two patients experienced prodromal abdominal pain and vomiting; all of them developed acute respiratory failure and collapse needing mechanical ventilation. Concomitant status epilepticus occurred in one patient. Lactic acidosis was present in all cases (20, 24 and 30 mM) necessitating extra-renal dialysis. Hepatic cytolysis was constant, contrasting with moderately increased CK levels (3 N to 5 N). No triggering factor could be identified. All patients fully recovered after prolonged intensive care, but resting lactate levels constantly remained elevated up to 8 mM. Muscle biopsy showed numerous ragged-red and COX-negative fibers in two patients, and lipidosis in the third one. Combined deficiency of mtDNA-dependant respiratory complexes was not explained by mtDNA depletion or deletion. Heteroplasmic pathogenic point mutations were detected in tRNA genes: MT-TL1 (m.3280G > A; m.3258C > T) and MT-TK (m8363A > G). Tissue distribution was heterogeneous for the MT-TL1 mutations but homogeneous for the MT-TK mutation. Life-threatening lactic acidosis may be inaugural or a major clinical manifestation in adults with mtDNA mutations. Prolonged intensive care may obtain dramatic and sustained improvement.