Unrecognized scale and clinical relevance of somatic mosaicism

摘要 生物体内细胞之间的几乎所有遗传物质都是相同的。然而，单核苷酸 变异体(SNV)、拷贝数变异体(CNV)和其他结构变异体不断累积为细胞 在发展中分裂。这个过程导致了一个由无数细胞组成的有机体，每个细胞都有自己的细胞 独特的基因组。因此，每个人无疑都是马赛克的。镶嵌突变可能不会被注意到，这是背后的原因 遗传性疾病或正常的人类变异，并可能作为体质遗传给下一代 变异并导致遗传性疾病的意外代际复发 父母没有受到影响的孩子，与孟德尔人的期望相反。日益增长的敏感性和 基因组技术的解析已经确定了SNV和CNV的嵌合体。组合体细胞 在患有多种遗传疾病的患者的父母中发现了生殖系嵌合体，因此 增加了通过常规血液测试而不是要求检测出嵌合体个体的可能性 生殖细胞的直接检查。然而，尽管它对人类健康有相当大的影响，但有系统的人口 种系和体细胞嵌合体的研究都很缺乏。与复发性CNV相反，通常由 在减数分裂过程中，通过非等位基因的同源重组，非复发的CNV被认为是由dna引起的。 复制错误，例如在有丝分裂过程中微同源介导的断裂诱导的复制或非 同源末端连接。新发非复发性CNV的复发风险 帐户随机机会和马赛克先前估计为~0.3%。我们的预赛 发表的关于100个无血缘关系的受影响家庭的数据表明，CNV的体细胞嵌合体存在于~4% 健康的父母。目前，CMA和WES的检测率分别为~20%和~25%，因此在 大约一半的患者没有发现致病变异。我们认为其中一些患者可能有 目前在CMA和WES中使用标准算法未检测到的马赛克致病变异。 未被识别的嵌合体也可以部分解释不同的表现力和不完全的外显。我们 假设相当数量的明显从头开始的SNV和CNV不是起源于减数分裂，而是出现 在受精卵后早期有丝分裂，这可以在受影响的患者或他们的健康人身上发现 父母。在目标1和目标2中，我们将在500名据称健康的父母中寻找低水平的体细胞嵌合体 受影响的儿童在其受影响的儿童中发现明显的新生CNV、INDELs或SNV。在AIM 2，我们将开发一种非侵入性产前检测方法，用于检测反复发生的突变，并与精子和精子数相关。 体细胞嵌合体。在目标3中，我们将研究无症状患者的体细胞马赛克CNV、INDELS和SNV。 在以往的临床或研究基因检测中已经发现了非马赛克致病变异。我们会估计 目前未被认识和了解甚少的体细胞嵌合体的患病率和临床后果 并介绍早期合子后突变和人类进化的分子机制。

ABSTRACT Nearly all of the genetic material among cells within an organism is identical. However, single-nucleotide variants (SNVs), copy-number variants (CNVs), and other structural variants continually accumulate as cells divide during development. This process results in an organism composed of countless cells, each with its own unique genome. Thus, every human is undoubtedly mosaic. Mosaic mutations can go unnoticed, underlie genetic disease or normal human variation, and may be transmitted to the next generation as constitutional variants and cause unexpected intergenerational recurrences of genetic disorders with multiple affected children born to unaffected parents, contrary to Mendelian expectations. The increasing sensitivity and resolution of genomic technologies have identified mosaicism for both SNVs and CNVs. Combined somatic and germline mosaicism has been identified in parents of patients with a number of genetic conditions, thus raising the possibility that mosaic individuals might be detected by routine blood tests rather than requiring direct examination of germ cells. Yet despite its considerable impact on human health, systematic population studies of both germline and somatic mosaicism are lacking. In contrast to recurrent CNVs, usually mediated by nonallelic homologous recombination during meiosis, nonrecurrent CNVs are thought to arise due to DNA replication errors, such as microhomology-mediated break-induced replication during mitosis or non- homologous end joining. Recurrence risks of putatively de novo nonrecurrent CNVs designed to take into account random chance and mosaicism have been previously estimated to be ~ 0.3%. Our preliminary published data on 100 unrelated affected families indicate that somatic mosaicism for CNVs is present in ~ 4% of healthy parents. Currently, the detection rates for CMA and WES are ~ 20% and ~ 25%, respectively, thus in about half of patients no pathogenic variant is found. We propose that some of these patients may have mosaic pathogenic variants that are currently undetected using standard algorithms in CMA and WES. Unrecognized mosaicism could also partially explain variable expressivity and incomplete penetrance. We hypothesize that a significant number of apparently de novo SNVs and CNVs are not meiotic in origin but arise during early post-zygotic mitoses and this can be identified either in the affected patients or their healthy parents. In Aims 1 and 2, we will search for low-level somatic mosaicism in reportedly healthy parents of 500 affected children who have apparent de novo CNVs, indels, or SNVs identified in their affected children. In Aim 2, we will develop a non-invasive prenatal test for detection of recurrent mutations and correlate sperm vs. somatic mosaicism. In Aim 3, we will study somatic mosaic CNVs, indels, and SNVs in patients in whom no nonmosaic pathogenic variant has been found in previous clinical or research genetic testing. We will estimate the currently unrecognized and poorly understood prevalence and clinical consequences of somatic mosaicism and inform about molecular mechanisms of early post-zygotic mutagenesis and human evolution.