Evaluation of the permissible mismatch concept

Abstract  Maruya et al. described a method of separating one HLA-A+B+DR mismatched transplants into permissible and immunogenic categories (published in Clinical Transplants 1993). For the permissible subgroup, they observed an outcome similar to that of zero-A+B+DR mismatched transplants. The classification was based on the HLA type combination of donor and recipient. We evaluated this concept with the data of the Collaborative Transplant Study (CTS). We did not obtain significant differences between the outcome of immunogenic and permissible mismatched transplants. The pair wise p-values for the comparison of zero-mismatched with permissible mismatched transplants are significant for cadaver transplants. The indifferent results obtained in our analysis do not support the concept of permissible mismatches. A more restrictive definition of the permissible mismatches might be helpful. The current method appears to be of insufficient reliability due to the relatively small numbers of transplants in the individual subgroups used to identify permissible combinations.     

Use of 5-fluorouracil and survival in patients with microsatellite-unstable colorectal cancer

BACKGROUND & AIMS: 5-Fluorouracil improves mortality in stage III colorectal cancer patients. In vitro studies suggest that microsatellite instability influences cell survival after 5-fluorouracil treatment. We investigated the survival influence of 5-fluorouracil in patients with microsatellite instability-high tumors. METHODS: We collected data and tumors on 204 consecutive stage II and III colorectal cancer patients from registries at the University of California and Veterans Administration hospitals in San Diego, California, from 1982 to 1999. Archival DNA was extracted, and microsatellite instability was assessed by National Cancer Institute-recommended markers. Cox proportional hazard modeling was used to determine survival associations for microsatellite instability and 5-fluorouracil treatment status. RESULTS: We identified 36 microsatellite instability-high (17.6%) and 168 non-microsatellite instability-high tumors (82.4%). Microsatellite instability-high tumors were significantly associated with proximal colon location, presence of mucin, and surrounding lymphoid reaction. Univariate and multivariate analyses showed no survival difference between microsatellite instability-high and non-microsatellite instability-high groups (hazard ratio, 1.04; P = 0.88). Dichotomized by use of 5-fluorouracil, there was increased risk of death in patients who received no adjuvant chemotherapy (hazard ratio, 2.02; P = 0.02). However, the benefit of 5-fluorouracil was different between microsatellite instability-high and non-microsatellite instability-high groups. Patients with non-microsatellite instability-high tumors who received 5-fluorouracil had better survival compared with patients who were not treated (P < 0.05). Conversely, patients with microsatellite instability-high tumors who were treated with 5-fluorouracil had no survival difference compared with patients without treatment (P = 0.52). CONCLUSIONS: There is improved survival in patients with non-microsatellite instability-high tumors after 5-fluorouracil-based chemotherapy that does not extend to patients with microsatellite instability-high tumors. The microsatellite instability status of a patient's colorectal cancer may indicate differences in 5-fluorouracil-based chemosensitivity; this is consistent with in vitro studies.     

Discrimination of speech and of complex nonspeech sounds of different temporal structure in the left and right cerebral hemispheres

The key question in understanding the nature of speech perception is whether the human brain has unique speech-specific mechanisms or treats all sounds equally. We assessed possible differences between the processing of speech and complex nonspeech sounds in the two cerebral hemispheres by measuring the magnetic equivalent of the mismatch negativity, the brain's automatic change–detection response, which was elicited by speech sounds and by similarly complex nonspeech sounds with either fast or slow acoustic transitions. Our results suggest that the right hemisphere is predominant in the perception of slow acoustic transitions, whereas neither hemisphere clearly dominates the discrimination of nonspeech sounds with fast acoustic transitions. In contrast, the perception of speech stimuli with similarly rapid acoustic transitions was dominated by the left hemisphere, which may be explained by the presence of acoustic templates (long-term memory traces) for speech sounds formed in this hemisphere.     

基于被动听觉ERP范式的慢性意识障碍患者个体评估研究

近年来,大脑功能检测技术逐渐应用于意识障碍(DoC)患者的意识水平评估,以期降低仅依靠临床主观行为量表评估的误诊率。其中,被动听觉事件相关电位(ERPs)范式下诱发的N1和失匹配负波(MMN)成分被认为是反应DoC患者意识水平的关键脑功能指标,但目前仍局限于组别层面的统计分析结果,其在DoC患者个体水平的评估效能尚待挖掘。根据N1和MMN成分的特性,提出了一种适用于被动听觉ERPs范式下DoC患者个体评估的深度学习算法。该方法引入了特征融合的数据扩增策略,即在单被试数据中随机抽取不同类型的试次进行空间级联形成新的融合样本,并结合EEGNET深度学习算法实现自动化特征提取和分类识别。在包含132名被试的单试次数据集上进行测试。对健康被试(38名),微意识状态(40名)和植物状态(54名)患者进行三分类评估。统计分析结果表明,该样本融合策略可显著提升模型分类表现,并在单被试融合样本数量扩增至1 000时模型取得样本水平75.14%的平均分类准确率,以及被试水平83.00%的平均分类准确率,83.79%的精确率和84.02%的召回率。所提出的深度学习框架可有效克服传统方法中存在的个体评估能力不强的问题,为DoC患者个体评估提供新的研究思路。     

Imaging of pannus formation in patients with mechanical heart valves

Patient-prosthesis mismatch (PPM) should be recognized in patients with elevated transprosthetic gradients but without leaflet immobility, since the treatment strategy may differ in either etiology. However, thrombus and/or pannus formation should be excluded before a diagnosis of PPM is made. Particularly, pannus formation may not be diagnosed with 2-dimensional transesophageal echocardiography. Electrocardiographically gated 64-section multidetector computed tomography (MDCT) may be a promising tool in diagnosing or excluding pannus formation. Our report underlines the utility of MDCT in this regard and also emphasizes the importance of recognition of PPM as a differential diagnosis in such patients.     

Brain activity from stimuli that are not perceived: Visual mismatch negativity during binocular rivalry suppression

Predictive coding explains visual perception as the result of an interaction between bottom‐up sensory input and top‐down generative models at each level of the visual hierarchy. Evidence for this comes from the visual mismatch negativity (vMMN): a more negative ERP for rare, unpredictable visual stimuli—deviants, than for frequent, predictable visual stimuli—standards. Here, we show that the vMMN does not require conscious experience. We measured the vMMN from monocular luminance‐decrement deviants that were either perceived or not during binocular rivalry dominance or suppression, respectively. We found that both sorts of deviants elicited the vMMN at about 250 ms after stimulus onset, with perceived deviants eliciting a bigger vMMN than not‐perceived deviants. These results show that vMMN occurs in the absence of consciousness, and that consciousness enhances the processing underlying vMMN. We conclude that generative models of visual perception are tested, even when sensory input for those models is not perceived.     

MutL traps MutS at a DNA mismatch

DNA mismatch repair (MMR) identifies and corrects errors made during replication. In all organisms except those expressing MutH, interactions between a DNA mismatch, MutS, MutL, and the replication processivity factor (β-clamp or PCNA) activate the latent MutL endonuclease to nick the error-containing daughter strand. This nick provides an entry point for downstream repair proteins. Despite the well-established significance of strand-specific nicking in MMR, the mechanism(s) by which MutS and MutL assemble on mismatch DNA to allow the subsequent activation of MutL’s endonuclease activity by β-clamp/PCNA remains elusive. In both prokaryotes and eukaryotes, MutS homologs undergo conformational changes to a mobile clamp state that can move away from the mismatch. However, the function of this MutS mobile clamp is unknown. Furthermore, whether the interaction with MutL leads to a mobile MutS–MutL complex or a mismatch-localized complex is hotly debated. We used single molecule FRET to determine that Thermus aquaticus MutL traps MutS at a DNA mismatch after recognition but before its conversion to a sliding clamp. Rather than a clamp, a conformationally dynamic protein assembly typically containing more MutL than MutS is formed at the mismatch. This complex provides a local marker where interaction with β-clamp/PCNA could distinguish parent/daughter strand identity. Our finding that MutL fundamentally changes MutS actions following mismatch detection reframes current thinking on MMR signaling processes critical for genomic stability.The DNA mismatch repair (MMR) system employs several proteins to locate and correct DNA replication errors that escape polymerase proofreading. Mutations in these proteins contribute to MMR dysfunction that is associated with carcinogenesis, such as Lynch syndrome and other diseases associated with high mutator phenotypes (1, 2). In all organisms, MMR is initiated by binding of MutS homologs to a base–base mismatch or an insertion/deletion loop (IDL), followed by ATP-dependent recruitment of MutL homologs to begin the process of repair (3, 4). Following MutL recruitment, a key event is the introduction of a nick that directs excision and resynthesis of the nascent DNA strand containing the error (5–7).In methyl-directed MMR, which occurs in Escherichia coli, the mismatch- and ATP-dependent MutS–MutL–DNA complex activates the protein MutH to nick transiently unmethylated d(GATC) sequences in the daughter strand. Notably, however, MutH is not widely conserved in prokaryotes and does not exist in eukaryotes. Recent in vitro studies of eukaryotic MMR indicate that in these MutH-free organisms, detection of a mismatch by MutS or MutSα [MutS(α)] licenses MutL(α) to interact with the processivity factor (β-clamp/PCNA), which in turn activates the latent endonuclease activity of MutL(α) to incise the daughter DNA strand on both the 3′ and 5′ sides of the error (8–11). The interaction between MutL and the β-clamp (or between MutLα and PCNA) provides the strand discrimination signal because the β-clamp (or PCNA) is loaded asymmetrically at the replication fork or at a nick in DNA (10, 12).The importance of the nicking activity of MutL homologs is highlighted by the observation that mutations that impair yeast MutLα endonuclease activity cause a significant mutator phenotype and genomic instability (11, 13, 14). Despite the well-established significance of strand-specific nicking in MMR, the mechanism(s) by which MutS and MutL assemble on mismatched DNA to allow subsequent activation of MutL endonuclease activity by β-clamp/PCNA remains elusive. There is general agreement that in both prokaryotes and eukaryotes, after binding a mismatch MutS or MutSα can undergo conformational changes to a mobile clamp state that can move away from the mismatch (6, 15). What happens after this step is mired in controversy. Several disparate models for MutS(α)–MutL(α) mismatch complex formation and the subsequent signaling of repair have been proposed (e.g., see refs. 6, 7, 15–21). One prominent model in the field has MutL(α) joining MutS(α) to form MutS(α)–MutL(α) sliding clamps that diffuse along the DNA to interact with the strand-discrimination signal (β-clamp/PCNA or MutH) (16). Other models include trapping of MutS(α) clamps near the mismatch by MutL(α) followed by DNA looping or, alternately, MutS(α)-induced polymerization of MutL(α) along the DNA to reach the strand-discrimination signal (6, 7, 15, 18, 22). Some degree of localization to the mismatch is suggested by in vitro studies of eukaryotic MMR proteins, indicating that although MutLα can introduce nicks across long stretches of DNA, they occur preferentially in the vicinity of the mismatch (9, 11, 12).In this study, we have used single molecule fluorescence to demonstrate that in the case of Thermus aquaticus (a MutH-free organism), MutL traps MutS at the mismatch after its ATP-induced activation but before its conversion into a sliding clamp. The resulting MutS–MutL mismatch complex typically contains more MutL than MutS, with one or two MutS dimers and up to four MutL dimers. MutS exists in a conformationally dynamic state within these complexes, which may be relevant for subsequent steps in MMR. In contrast to a mobile MutS–MutL complex, localization of MutS–MutL at the mismatch can restrict β-clamp/PCNA-activated MutL nicking to the vicinity of the mismatch, thereby enhancing MMR efficiency and limiting excessive excision and resynthesis that can destabilize the genome.     

Compound heterozygosity for two novel mutations in a severe factor XI deficiency

We identified two novel mutations in an asymptomatic 25-year-old Japanese patient with severe factor XI deficiency. Direct sequencing analysis of PCR products from his factor XI gene revealed a G to T transversion in exon 12, resulting in the nonsense mutation (Glu447Stop) and a G insertion in five consecutive guanine nucleotides ((501)Trp(TGG)-(502)Gly(GGG)) in exon 13 that is expected to lead to the substitution of the last 105 amino acids ((503)Tyr-(607)Val) with 32 abnormal amino acid residues ((503)Val-(534)Thr) followed by stop codon. We also demonstrated that two mutations are associated with the separate alleles in this patient, indicating compound heterozygosity for these mutations. Both mutations lead to the disruption of the catalytic domain structure of the FXI molecule and thus are responsible for his deficiency of factor XI.     

TS表达与MMR状态联合检测在结直肠癌预后中的研究进展

胸苷酸合成酶(thymidylate synthetase, TS)是5-Fu(5-fluorouraci)发挥抗代谢作用治疗胃肠道恶性肿瘤的重要作用靶点,TS mRNA及蛋白表达与5-FU类药物的敏感性和抗药性密切相关。DNA错配修复MMR蛋白缺乏可以引起微卫星不稳定(microsatellite instability,MSI)。MSI亚型与5-FU类药物的疗效及结直肠癌患者预后相关。目前,将TS表达或MMR状态单独作为结直肠癌预后因子仍存在争议,因此联合检测TS表达与MMR状态 来判断结直肠癌患者预后的研究受到越来越多的关注。