235 research outputs found
Statistical inference in two-sample summary-data Mendelian randomization using robust adjusted profile score
Mendelian randomization (MR) is a method of exploiting genetic variation to
unbiasedly estimate a causal effect in presence of unmeasured confounding. MR
is being widely used in epidemiology and other related areas of population
science. In this paper, we study statistical inference in the increasingly
popular two-sample summary-data MR design. We show a linear model for the
observed associations approximately holds in a wide variety of settings when
all the genetic variants satisfy the exclusion restriction assumption, or in
genetic terms, when there is no pleiotropy. In this scenario, we derive a
maximum profile likelihood estimator with provable consistency and asymptotic
normality. However, through analyzing real datasets, we find strong evidence of
both systematic and idiosyncratic pleiotropy in MR, echoing the omnigenic model
of complex traits that is recently proposed in genetics. We model the
systematic pleiotropy by a random effects model, where no genetic variant
satisfies the exclusion restriction condition exactly. In this case we propose
a consistent and asymptotically normal estimator by adjusting the profile
score. We then tackle the idiosyncratic pleiotropy by robustifying the adjusted
profile score. We demonstrate the robustness and efficiency of the proposed
methods using several simulated and real datasets.Comment: 59 pages, 5 figures, 6 table
Aggregating Dependent Signals with Heavy-Tailed Combination Tests
Combining dependent p-values to evaluate the global null hypothesis presents
a longstanding challenge in statistical inference, particularly when
aggregating results from diverse methods to boost signal detection. P-value
combination tests using heavy-tailed distribution based transformations, such
as the Cauchy combination test and the harmonic mean p-value, have recently
garnered significant interest for their potential to efficiently handle
arbitrary p-value dependencies. Despite their growing popularity in practical
applications, there is a gap in comprehensive theoretical and empirical
evaluations of these methods. This paper conducts an extensive investigation,
revealing that, theoretically, while these combination tests are asymptotically
valid for pairwise quasi-asymptotically independent test statistics, such as
bivariate normal variables, they are also asymptotically equivalent to the
Bonferroni test under the same conditions. However, extensive simulations
unveil their practical utility, especially in scenarios where stringent type-I
error control is not necessary and signals are dense. Both the heaviness of the
distribution and its support substantially impact the tests' non-asymptotic
validity and power, and we recommend using a truncated Cauchy distribution in
practice. Moreover, we show that under the violation of quasi-asymptotic
independence among test statistics, these tests remain valid and, in fact, can
be considerably less conservative than the Bonferroni test. We also present two
case studies in genetics and genomics, showcasing the potential of the
combination tests to significantly enhance statistical power while effectively
controlling type-I errors
Statistical inference in two-sample summary-data Mendelian randomization using robust adjusted profile score
Melatonin enhances the anti-tumor effect of fisetin by inhibiting COX-2/iNOS and NF-κB/p300 signaling pathways.
Melatonin is a hormone identified in plants and pineal glands of mammals and possesses diverse physiological functions. Fisetin is a bio-flavonoid widely found in plants and exerts antitumor activity in several types of human cancers. However, the combinational effect of melatonin and fisetin on antitumor activity, especially in melanoma treatment, remains unclear. Here, we tested the hypothesis that melatonin could enhance the antitumor activity of fisetin in melanoma cells and identified the underlying molecular mechanisms. The combinational treatment of melanoma cells with fisetin and melatonin significantly enhanced the inhibitions of cell viability, cell migration and clone formation, and the induction of apoptosis when compared with the treatment of fisetin alone. Moreover, such enhancement of antitumor effect by melatonin was found to be mediated through the modulation of the multiply signaling pathways in melanoma cells. The combinational treatment of fisetin with melatonin increased the cleavage of PARP proteins, triggered more release of cytochrome-c from the mitochondrial inter-membrane, enhanced the inhibition of COX-2 and iNOS expression, repressed the nuclear localization of p300 and NF-κB proteins, and abrogated the binding of NF-κB on COX-2 promoter. Thus, these results demonstrated that melatonin potentiated the anti-tumor effect of fisetin in melanoma cells by activating cytochrome-c-dependent apoptotic pathway and inhibiting COX-2/iNOS and NF-κB/p300 signaling pathways, and our study suggests the potential of such a combinational treatment of natural products in melanoma therapy
A Comparative Study of Z mediated Charged Lepton Flavor Violation at future lepton colliders
Charged lepton flavor violation (CLFV) represents a transition between
charged leptons of different generations that violates lepton flavor
conservation, which is a clear signature of possible new physics beyond the
standard model. By exploiting a typical example model of extra Z
gauge boson, we perform a detailed comparative study on CLFV searches at
several future lepton colliders, including a 240 GeV electron-positron collider
and a TeV scale muon collider. Based on detailed signal and background
Monte-Carlo studies with fast detector simulations, we derive the potentials in
searching for Z mediated CLFV couplings with , and
of different future colliders. The results are compared with the
current limits set by either low-energy experiments or the high-energy LHC
experiments. We find that the sensitivity of the related CLFV coupling
strength at future lepton colliders will be significantly improved comparing
with the current best constraints.Comment: 11 pages, 5 figure
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