Acylcarnitine profile mimicking multiple acyl-CoA dehydrogenase deficiency in a patient with mitochondrial myopathy and a mutation in MT-CO2

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Abstracts 2017 / Neuromuscular Disorders 27 (2017) S96–S249

has decreased protease and ATPase activity in vitro compared to wild-type Lon. Fibroblasts from both patients had elevated intracellular lactate and reduced spare respiratory capacity compared to parental fibroblasts, with reduced activity of mitochondrial complex I. Muscle biopsies revealed scattered COX negative fibres. The patients we describe have a distinct clinical presentation compared to those previously described with CODAS syndrome. This is likely due to the p.Pro761Leu mutation being located in the proteolytic domain of the protein rather than the ATPase domain, and expands the clinical spectrum of LONP1-related disorders. http://dx.doi.org/10.1016/j.nmd.2017.06.095

P.66 Acylcarnitine profile mimicking multiple acyl-CoA dehydrogenase deficiency in a patient with mitochondrial myopathy and a mutation in MT-CO2 S. Roos 1, K. Sofou 2, C. Hedberg-Oldfors 1, G. Kollberg 1, U. Lindgren 1, C. Thomsen 1, J. Asin-Cayuela 1, M. Tulinius 2, A. Oldfors 1 1 University of Gothenburg, Institute of Biomedicine, Gothenburg, Sweden; 2 The Queen Silvia Children’s Hospital, Sahlgrenska University Hospital, Gothenburg, Sweden We present a 16-year-old girl with a life-long history of exercise intolerance. Laboratory investigations showed increased serum levels of acylcarnitines and increased urinary excretion of lactate and 2-hydroxyglutarate, consistent with multiple acyl-CoA dehydrogenase deficiency (MADD). Blood tests showed normal serum CK, increased liver transaminases and lactate, and mild anemia. Biochemical analyses of skeletal muscle mitochondria revealed an isolated and extremely low activity of cytochrome c oxidase (COX). Enzyme histochemical investigations showed abnormal mitochondrial proliferation and very few fibers with normal COX activity. Next generation sequencing revealed a one-base pair deletion (m.8088delT) in the MT-CO2 gene, which encodes subunit 2 of COX, resulting in a premature stop codon. RFLP-analysis showed that the level of heteroplasmy was > 95% in muscle, and between 2–15 % in other examined tissues (hair, blood, fibroblasts, buccal swabs, and urinary sediment). The mutation was not identified in the asymptomatic mother, suggesting a de novo mutation. Preliminary single-fiber PCR analysis data indicate that the proportion of mutated mtDNA correlates with enzyme histochemical COX deficiency. Immunohistochemistry of three mtDNA encoded subunits (MTCO1, MT-CO2, MT-CO3) and the nuclear encoded subunit 4 (COX4) of COX demonstrated that only COX-positive cells express MT-CO2 and MT-CO3, while expression of MT-CO1 and COX4 was present in COX-negative cells, albeit to a lesser extent. There was no difference in the protein expression of NDUFB8, a nuclear encoded subunit of Complex I, or VDAC1, serving as a marker for mitochondrial mass, between normal and COX-deficient cells. Only a few pathogenic mutations have been reported in MT-CO2, causing COX deficiency with heterogeneous clinical manifestations. Our results indicate that the reported MT-CO2 mutation is pathogenic and that respiratory chain deficiency may cause an acylcarnitine profile suggestive of MADD. http://dx.doi.org/10.1016/j.nmd.2017.06.096

P.67 Integrated genome analysis of COX deficiency in Japan K. Takayama 1, A. Iida 2, S. Noguchi 1, I. Nonaka 1, Y. Goto 2, I. Nishino 1 1 National Institute of Neuroscience, NCNP, Tokyo, Japan; 2 Medical Genome Center, NCNP, Tokyo, Japan Cytochrome c oxidase (COX) deficiency is a genetically heterozygous mitochondrial disease characterized by myopathy, encephalopathy and cardiomyopathy. Defects of nuclear genes as well mitochondrial (mt) genes cause this disease. However, the mutation frequencies of the causative genes have largely unknown in Japan. To evaluate mutations of nuclear genes in

COX deficiency more extensively, we conducted exome sequencing in Japanese patients. A total of 58 unrelated patients with COX deficiency were recruited from collaborative universities and hospitals in Japan. We diagnosed all patients by muscle pathology at our research institute. We then screened mutations of mtDNA in all samples by MiSeq and excluded them. We performed exome sequencing in mtDNA mutation-negative samples. We also stained COX activities by histochemical and electron microscopy (EM) in several patients who have pathogenic mutations. Mutations in mtDNA were found in 18 patients with COX deficiency. We then performed exome sequencing in 40 patients and found 23 patients in four genes, SURF1, ETHE1, AIFM1 and RRM2B. SURF1 was the most frequently mutated gene with mutational frequency of 40% (16/40 patients). Mutation frequencies in ETHE1 and AIFM1 were 10% (4/40) and 5% (2/40), respectively. RRM2B mutation was seen in one patient (2.5%). We also found a common mutation, c.743C > A (p.A248D), in exon 7 of SURF1 which were shared by nine patients. COX signal was faint in the muscle from the patient with SURF1 mutation on COX electron microscopy, but not on histochemical stain. In addition, structural abnormalities of mitochondria in ETHE1-mutated tissues were detected. This is the first report of large-scale genome analysis of COX deficiency in Japan. A total of 41 in 58 patients were detected (71%). The mutation list of COX deficiency should be helpful for future clinical sequencing and also for analyzing correlation between patient’s mutations and phenotypes. http://dx.doi.org/10.1016/j.nmd.2017.06.097

P.68 Correlation of serum biomarkers and magnetic resonance spectroscopy (MRS) in monitoring disease progression in patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) due to mtDNA A3243G mutation H. Lee 1, Y. Lee 2 1 Yongin Severance Hospital, Seoul, Republic of Korea; 2 Gangnam Severance Hospital, Seoul, Republic of Korea Analysis of serum biomarkers, including lactate and the lactate-to-pyruvate (Lac/Pyr) ratio, and magnetic resonance spectroscopy (MRS) are useful for monitoring disease progression in patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). We aim to evaluate the correlation of serum biomarkers and MRS parameters during changes associated with stroke-like episodes. Thirteen symptomatic MELAS patients carrying the A3243G mutation were recruited and a total of 207 voxels from 41 MRS studies were divided into 3 groups according to the temporal association with stroke-like episodes. The MRS NAA/Cr, Cho/Cr, NAA/Cho ratios, and the presence of a lactate peak were evaluated. Serum biomarkers, serum lactate level, and the Lac/Pyr ratio were determined. In regions with acute infarcts, the severity of serum Lac/Pyr and that of the MRS lactate peak (r = 0.503, P = 0.0007) correlated; there was a weak positive correlation with serum lactate (r = 0.361, P = 0.02), severity of elevated serum lactate (r = 0.318, P = 0.04), and serum Lac/Pyr (r = 0.365, P = 0.02). In previously infarcted regions, there was a statistically significant weak correlation between the severity of the MRS lactate peak and serum Lac/Pyr (r = 0.203, P = 0.03), as well as the severity of serum Lac/Pyr (r = 0.213, P = 0.02). In structurally normal regions, we found a statistically significant weak to moderate negative correlation between serum lactate and MRS NAA/Cr (r = -0.437, P = 0.008), and between the severity of elevated serum lactate and MRS NAA/Cr (r = -0.501, P = 0.002) as well as MRS NAA/Cho (r = -0.386, P = 0.02). MRS is useful for monitoring changes in brain metabolites, and certain changes in MRS parameters correlate with specific serum biomarkers, in relation to temporal relation to stroke-like episodes. Accurate interpretation of serum and MRS studies in relation to the patients’ clinical status will facilitate disease monitoring and care management of MELAS patients. http://dx.doi.org/10.1016/j.nmd.2017.06.098