Unrecognized scale and clinical relevance of somatic mosaicism

摘要 在一个有机体中，几乎所有细胞的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）和其他结构变异体在细胞中不断积累， 在发展中分化。这一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。镶嵌突变可能会被忽视， 遗传疾病或正常的人类变异，并可能传递给下一代作为宪法 变异，并导致遗传性疾病的意外代际复发， 与孟德尔理论相反，父母不受影响的孩子。敏感性的提高， 基因组技术的解析已经鉴定了SNV和CNV的嵌合现象。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， 这增加了通过常规血液测试而不是要求 直接检查生殖细胞。然而，尽管它对人类健康有相当大的影响， 缺乏对生殖系和体细胞嵌合现象的研究。与复发性CNV相反，通常介导 通过减数分裂期间的非等位基因同源重组，非重复性CNV被认为是由于DNA 复制错误，如有丝分裂期间微同源介导的断裂诱导的复制或非 同源末端连接原发性非复发性CNV的复发风险，旨在考虑 帐户随机机会和镶嵌性先前估计约为0.3%。我们的初步 对100个不相关的受影响家庭的公开数据表明，CNVs的体细胞嵌合体存在于~4%的家庭中。 健康的父母。目前，CMA和WES的检出率分别为~20%和~25%，因此， 大约一半的患者没有发现致病性变异。我们认为，这些患者中的一些可能有 镶嵌致病变异，目前未检测到使用标准算法在CMA和WES。 未识别的镶嵌现象也可以部分解释可变的表达和不完全的表达。我们 假设大量明显的从头SNV和CNV不是减数分裂起源的， 在早期合子后有丝分裂，这可以确定无论是在受影响的患者或他们的健康 父母在目标1和2中，我们将在500名健康的父母中寻找低水平的体细胞嵌合体。 在受影响儿童中鉴定出明显的从头CNV、插入缺失或SNV的受影响儿童。在aim中 2、我们将开发一种非侵入性的产前检测方法，用于检测复发性突变，并将精子与 体细胞镶嵌现象在目标3中，我们将研究在没有基因突变的患者中的体细胞嵌合CNV、插入缺失和SNV。 非嵌合体致病性变异已在先前的临床或研究遗传检测中发现。我们估计 目前尚未认识到和了解甚少的患病率和临床后果的体细胞镶嵌 并告知早期后合子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.