Characterization of Cardiac Mitochondrial DNA in Donors with Down Syndrome

描述（由申请人提供）：儿科白血病的治疗方案严重依赖于蒽环类药物柔红霉素和多柔比星的使用。患有唐氏综合征（DS）的儿童癌症患者构成了蒽环类药物相关心脏毒性风险特别高（相对风险为3.4倍）的人群。儿童肿瘤学小组记录了17.5%的接受含蒽环类药物方案治疗急性髓性白血病的DS儿童发生心肌病。我们推测，DS患者心脏中线粒体DNA（mtDNA）的预先存在的改变有助于增强蒽环类药物的心脏毒性。尚未研究DS患者心脏mtDNA改变的程度和类型。在具体目标1中，我们将检查11个DS供体心脏样本和22个年龄匹配的无DS供体样本中mtDNA缺失的存在和频率。线粒体DNA缺失的存在和频率将采用灵敏的“单分子”长距离聚合酶链反应进行研究。将通过克隆和直接测序来表征单个mtDNA缺失变体，以鉴定受影响的基因并精确绘制mtDNA断裂点。在目标2中，将通过Ambry Genetics最先进的平行测序系统对线粒体基因组进行直接测序，记录DS供体心脏样本中存在的mtDNA突变。平行测序系统允许检测和表征>5%水平的线粒体全基因组异质性。为了进行比较，将在来自年龄和性别匹配的无DS供体的心脏样本中研究mtDNA变体的存在。具有致病潜力的多态性mtDNA变体和突变将通过详细的序列注释来鉴定，并辅以生物信息学资源，如MITOMAP和PhyloTree。这项工作的完成将为DS患者心脏mtDNA异常程度提供一个新的目录。这项工作将为与儿童肿瘤学小组的研究人员进行合作研究提供合理的基础，以确定mtDNA的特定改变在多大程度上影响患有DS的儿童癌症幸存者的心脏毒性风险。

DESCRIPTION (provided by applicant): Treatment regimens for pediatric leukemia rely heavily on the use of the anthracyclines daunorubicin and doxorubicin. Pediatric cancer patients with Down syndrome (DS) constitute a population at particularly greater risk (3.4-fold relative risk) for anthracycline-related cardiotoxicity. The Children's Oncology Group has documented development of cardiomyopathy in 17.5% of children with DS treated for acute myeloid leukemia with an anthracycline-containing regimen. We hypothesize that preexistent alterations in mitochondrial DNA (mtDNA) in the hearts of individuals with DS contribute to enhance the cardiotoxicity of anthracyclines. The extent and type of mtDNA alterations in hearts from individuals with DS have not been investigated. In specific aim 1, we will examine the presence and frequency of deletions in mtDNA in 11 heart samples from donors with DS and 22 samples from age-matched donors without DS. The presence and frequency of mtDNA deletions will be investigated with a sensitive "single molecule" long distance polymerase chain reaction. Individual mtDNA deletion variants will be characterized by cloning and direct sequencing to identify the affected genes and to precisely map mtDNA breakpoints. In aim 2, the presence of mtDNA mutations in heart samples from donors with DS will be documented by direct sequencing of the mitochondrial genomes with a state of the art parallel sequencing system at Ambry Genetics. The parallel sequencing system allows detection and characterization of mitochondrial genome-wide heteroplasmies at the >5% level. For comparison, the presence of mtDNA variants will be investigated in heart samples from age- and sex- matched donors without DS. Polymorphic mtDNA variants and mutations with pathogenic potential will be identified by detailed sequence annotations assisted by bioinformatics resources such as MITOMAP and PhyloTree. Completion of the proposed work will provide a novel catalogue on the extent of mtDNA abnormalities in hearts from individuals with DS. This work will provide a rational foundation for collaborative studies with investigators from the Children's Oncology Group to determine the extent to which specific alterations in mtDNA influence the risk of cardiotoxicity among survivors of pediatric cancers with DS.