Mitochondrial diabetes and mitochondrial DNA mutation burden in mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes syndrome

Abstract

Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is a very rare, diverse group of syndromes that mainly affect the central nervous system and skeletal muscles. The phenotypic variability is, at least in part, due to heteroplasmy with varying proportions of mutant and wild type mitochondrial DNA (MtDNA) molecules in different tissues. There may be close links between some types of mitochondrial diseases and diabetes mellitus (DM), however the genetic link between MELAS syndrome and DM has not been studied in depth. The clinical relationship between mitochondrial diabetes and mutant burden has rarely been studied through quantitative analysis in MELAS syndrome. We investigated the associations between clinical features and mutant burden in patients with MELAS syndrome with mitochondrial diabetes. From 2008 to 2018, of 57 subjects with suspected MELAS syndrome, 32 subjects were diagnosed as MELAS syndrome with mtDNA A-to-G transition at nucleotide 3243. Of the 32 patients with confirmed MELAS syndrome, mutation burden studies and next generation sequencing (NGS) were performed on 25 people. We analyzed NGS results and examined disease-related clinical variables, including age at symptom onset, age at diagnosis, lead time to diagnosis, and type of first symptoms. We also investigated lactic acidosis and pathological features indicating myopathies, biochemical enzyme assays for mitochondrial respiratory chain complex, neuroimaging, and syndromic diagnosis. Quantitative analysis for heteroplasmy of mutant burden was performed by counting the number of reads for each sequenced template by NGS. The mean mutation burden was 60.2 ± 18.8 % (range 22.5-100). Of the 25 subjects with NGS results, 15 (60%) were diagnosed with DM and two (8%) were diagnosed with impaired glucose tolerance (IGT). The mutation burden of subjects was strongly inversely correlated with first symptom onset and age at diagnosis of MELAS syndrome. However, mutation burden was not correlated with the clinical severity, auxological data, various clinical parameters, or progression of DM/IGT. The number of subjects with DM/IGT was lower in the high-mutant burden group compared to the low-mutant burden group. There was no significant difference in insulin resistance or sensitivity indices between the low- and high-mutation burden groups. Oral glucose tolerance test (OGTT) was performed for 14 subjects of the 25 subjects. Using the results, we calculated the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR), HOMA-%S, HOMA-%B, quantitative insulin sensitivity check index (QUICKI), and Matsuda index from to investigate insulin resistance and pancreatic beta cell function. We analyzed data of the DM/IGT subgroup and found that overall data were similar with the data from the total subjects. During the 3.7 year follow-up period, height standard deviation score (SDS) and weight SDS decreased, however, body mass index SDS was maintained. C-peptide, insulin, HOMA-IR, HOMA-%S, HOMA-%B, QUICKI, and Matsuda index were not significantly different between baseline and at follow-up. Mutation burden of subjects with DM/IGT were strongly inversely correlated with age at diagnosis of MELAS and age at diagnosis of DM/IGT; but not correlated with the clinical severity, auxological data, clinical parameters, or progression of DM/IGT. We investigated the association between several clinical parameters and mutation burden in patients with MELAS syndrome with mitochondrial diabetes through NGS. This study revealed that the mutation burden of patients with MELAS syndrome was significantly inversely correlated with first symptom onset, age at diagnosis of MELAS, and the onset time of DM/IGT, but not correlated with clinical severity, treatment outcome, or progression of DM/IGT. From these results, we can infer that the mutation burden in MELAS syndrome is significantly associated with the onset of symptoms and associated diseases, including mitochondrial diabetes. However, post-natal factors such as environmental effect may influence disease progression.

멜라스 증후군은 주로 신경 근육계를 침범하는 매우 드문 미토콘드리아 병증의 하나이다 이 질환의 표현형은 유전자 부담에 따라 매우 다양하게 나타난다 . 당뇨병도 그 중 하나이며 표현형과 유전형의 관계에 대해 많이 알려져 있지 않다 . 본 연구자는 차세대 염기서열 분석법을 이용하여 유전자 돌연변이 부담에 대해 정량적 분석을 진행하였고 소아청소년과 젊은 성인 멜라스 증후군에서 나타나는 미토콘드리아 당뇨병과의 관련성에 대해 집중적으로 연구하였다 전체 57 명의 멜라스 증후군 의심 환자 중 32 명이 미토콘드리아 유전자 3243 A>G 변이가 확인되었고 이 중 25 명에 대해 유전자 돌연변이 정량적 분석을 진행하였다 전체 대상자들의 각종 신경학적 임상지표 호르몬 검사 시행 결과를 연구하였고 이 중 14 명에 대해 경구당부하검사를 실시하였고 인슐린 저항성 / 민감성 지표를 계산하였다 유전자 돌연변이는 평균 60.2% 였으며 대상자 중 15 명 60%) 가 당뇨병 2 명 ( 이 내당능장애였다 돌연변이 부담은 증상 발현 나이 멜라스 증후군 진단 나이와 강한 음의 상관 관계를 보였으나 임상적 중증도 신체 계측 지수 신경학적 지표 당뇨병 경과와는 의미있는 상관 관계를 보이지 않았다 당뇨병 환자가 높은 돌연변이 부담군에서 더 많지 않았고 , 인슐린 저항성 민감성 지표가 돌연변이 부담에 따라 차이가 나지 않았다 당뇨병 과 내당능장 애 환자만을 대상으로 하위군 분석을 진행한 결과 역시 유사했다 3.7 년의 추적 관찰 기간 동안 신장 체중 표준편차점수가 떨어졌으나 체질량지수는 차이가 없었다 추적 기간 동안 인슐린 분비능 , 인슐린 저항성 민감성 지표 역시 큰 변화를 보이지 않았으나 멜라스 증후군 진단 연령 당뇨병 진단 연령은 돌연변이 부담과 강한 음의 상관 관계를 보였다 본 연구자는 차세대 염기서열 분석방법을 이용하여 확진된 멜라스 증후군 환자를 대상으로 유전자 돌연변이 부담 에 대한 정량 분석을 실시하였다 이를 통해 돌연변이 부담이 증상 발현 나이 , 멜라스 증후군 진단 연령 당뇨병 진단 연령과 강한 음의 상관 관계를 보임을 밝혔고 임상 경과 치료 반응 및 당뇨병 경과와는 관련이 없음을 확인하였다 본 연구에서 유전자 부담에 따라 증상 발현 질병 발생이 관련되지만 이후의 질병 경과 및 예후 는 유전자 부담 의 영향은 적고 출생 이후의 다양한 요인들에 의해 영향 받음 을 확인하여 보고하는 바이다.