Somatic Mosaicism in the Wiskott-Aldrich Syndrome

描述（由申请人提供）：体细胞嵌合体已在几种遗传性疾病中被描述，包括原发性免疫缺陷疾病（如Wiskott-Aldrich综合征[WAS]、x连锁严重联合免疫缺陷）、范可尼贫血、大泡性epidermolyysis和酪氨酸血症。虽然在WAS患者中观察到体细胞嵌合体（由原始野生型序列的逆转或由第二位点逆转突变引起）的频率很高，并且显然是疾病的一个重要方面，但我们对这一现象的理解目前严重有限。我们最近在WAS患者中发现了前所未有的逆转基因型多样性，挑战了目前关于自发逆转是罕见事件且其发生仅限于长寿祖细胞的观点。相反，我们的数据与一个模型是一致的，在这个模型中，自发的WAS突变以一定的频率起源于体细胞；然后，这些细胞被体内选择作用于那些部分或完全恢复WAS蛋白（WASp）功能的细胞。我们提出了一种新的视角来看待体细胞嵌合体现象——在种系WAS突变附近的体细胞突变谱本质上探索了可能的WASp氨基酸序列，最终倾向于那些在体内选择中具有足够适应性的氨基酸序列。在这项初步研究中，我们建议首先全面检查WAS患者中反向基因型探索的WAS DNA序列空间。其次，我们将研究这些反向基因型探索的WASp适应度景观，重点关注WASp在t淋巴细胞中的几个关键功能。我们提出，从进化生物学的角度观察WAS体细胞嵌合现象，为理解WAS可逆突变的起源和携带这些突变的细胞的体内选择提供了一个概念框架。公共卫生相关性：本探索性研究旨在确定遗传性遗传病（特别是Wiskott-Aldrich综合征）患者体内嵌合体发展的关键事件。

DESCRIPTION (provided by applicant): Somatic mosaicism has been described in several genetic diseases including Primary Immunodeficiency Diseases (e.g. Wiskott-Aldrich Syndrome [WAS], X-linked Severe Combined Immunodeficiency), Fanconi Anemia, Epidermolysis Bullosa, and Tyrosinemia. Although somatic mosaicism (resulting either from a reversion to the original wild-type sequence or from a second-site revertant mutation) is observed in a high frequency of patients with WAS and is clearly an important aspect of disease, our understanding of this phenomenon is presently severely limited. Our recent identification of an unprecedented diversity of revertant genotypes in a WAS patient challenges the current notion that spontaneous reversions are rare events and that their occurrence is restricted to long-lived progenitors. Rather, our data are consistent with a model in which spontaneous WAS mutations originate with some frequency in somatic cells; these cells are then are acted upon by in vivo selection enriching those with partial or full restoration of WAS protein (WASp) function. We propose a novel perspective in which to view somatic mosaicism - in which the spectrum of somatic mutations in the vicinity of a germ-line WAS mutation essentially explores the landscape of possible WASp amino acid sequences, ultimately favoring those with sufficient fitness for in vivo selection. In this pilot study, we propose to first comprehensively examine the WAS DNA sequence space explored by revertant genotypes in this WAS patient. Second, we will examine the WASp fitness landscape explored by these revertant genotypes, focusing on several critical functions of WASp in T-lymphocytes. We propose that viewing WAS somatic mosaicism from an evolutionary biology perspective offers a conceptual framework for understanding the origination of revertant WAS mutations and the in vivo selection of cells bearing these mutations. Public Health Relevance: This exploratory study seeks to identify critical events in the development of somatic mosaicism in patients with inherited genetic disease - in particular, the Wiskott-Aldrich Syndrome.