GENOMIC INSTABILITY IN FAMILIAL CANCER SYNDROMES

微卫星是基因组中的DNA片段，由重复n次的1至6个核苷酸的短核苷酸序列组成。基因组中有数千个这样的基因，它们由其独特的侧翼区域单独定义，因此可以通过PCR进行扩增，因此可以可视化。它们是多态性的（作为等位基因的重复数）并且通常稳定遗传，尽管显示在等位基因的序列重复数上发生突变）并且通常稳定遗传，尽管以可感知的频率（0.01-0.0001）在序列重复数上发生突变。在某些类型的肿瘤中，由于错配修复基因的缺陷，它们已被证明是高度不稳定的。其他位点的缺陷也可能导致这种不稳定性。具体的微卫星位点不稳定性（MSI）的定量措施尚未开发。我们已经开发了一种程序，小池PCR（SP-PCR）能够进行定量，并结合高通量荧光方法来筛选MSI的频率在小卫星位点。我们将把这些技术用于遗传多种癌症易感性Li/Fraumeni综合征（LFS）和Wilms肿瘤综合征（WT）的家庭，并回答一系列问题。不同类型的LFS肿瘤和WT肿瘤的不稳定性水平如何？p53突变的肿瘤与未发现p53突变的家族肿瘤的不稳定性是否不同，这些差异是否反映了导致不稳定性的不同基因座？同样的问题也会被问到候选基因与19 q连锁的家族中的WT肿瘤，而不是与19 q连锁的家族。LFS患者培养的成纤维细胞从早衰到永生化再到肿瘤形成，何时表现出不稳定性？遗传了癌症基因的患者与其未受影响的同胞的“正常”周围组织和外周血淋巴细胞中的不稳定性是否可检测到且在数量上存在差异？这些差异是否可以用于那些导致疾病的突变未知的家庭的症状前诊断？

Microsatellites are DNA stretches in the genome composed of repeats of short nucleotide sequences one to six nucleotides repeated n times. There are thousands of these in the genome and they are individually defined by their unique flanking regions and therefore amplifiable (by PCR) and so visualized. They are polymorphic (as number of repeats at an allele) and generally stably inherited, although shown to mutate in number of sequence repeats at an allele) and generally stably inherited, alth0ugh sown to mutate in number of sequence repeats at appreciable frequencies (0.01-0.0001). In certain types of tumors they have been shown to be highly unstable due to deficiencies in mismatch repair genes. Deficiencies at other loci may also enable such instability. Quantitative measures of specific microsatellite locus instability (MSI) have not been developed. We have developed a procedure, small pool PCR (SP-PCR) capable of carrying out that quantitation and coupled that with a high throughput fluorescent method to screen for MSI at frequencies at minisatellite loci. We will direct these techniques to families inheriting multiple cancer predisposition Li/Fraumeni Syndrome (LFS) and Wilms tumor syndrome (WT) and answer a series of questions. What is the level of instability in LFS tumors of different types and WT tumors? Is instability different in tumors with p53 mutation as opposed to tumors in families where p53 mutation have not been identified, and do those differences reflect different loci responsible for instability? The same question will be asked about WT tumors in families were the candidate gene is linked to 19q versus those where it is not. When is instability manifested in cultured fibroblasts from LFS patients as cells pass from pre-senescence to immortalization to tumor forming? Is instability detectable and quantitatively different in the "normal" surrounding tissue and peripheral blood lymphocytes of patients inheriting the gene responsible for cancer versus their unaffected sibs? Can those differences be used for presymptomatic diagnosis in families where the mutation responsible for the disorder is not known?