The comparability of whole-blood RNA-seq data across heterogeneous human cohorts remains a critical challenge for transcriptomic research. In this study, we analyzed baseline fasting whole blood RNA-seq profiles from three distinct cohorts (non-elite athletes, individuals with familial venous thrombosis, and participants in an obesity study) to quantify non-biological variance and evaluate normalization strategies for improving cross-dataset integration. Two common approaches, transcripts per million (TPM) and counts per million (CPM), were compared in combination with batch effect correction. Principal Component Analysis (PCA) showed that TPM normalized data failed to achieve meaningful alignment across cohorts even after batch correction. In contrast, CPM normalization combined with batch effect correction more effectively reduced unwanted technical variation and improved cross-cohort alignment. Further, we assessed housekeeping gene stability and identified SDHA, GUSB, and TBP as the most suitable housekeeping genes for whole blood RNA-seq, providing reliable internal references for normalization and dataset comparability. Collectively, our findings underscore the importance of selecting appropriate normalization strategies and leveraging stable housekeeping genes as critical for improving cross-cohort comparability in whole blood transcriptomic studies.

BACKGROUND: Quantitative trait locus (QTL) mapping in genetic data often involves analysis of correlated observations, which need to be accounted for to avoid false association signals. This is commonly performed by modeling such correlations as random effects in linear mixed models (LMMs). The R package lme4 is a well-established tool that implements major LMM features using sparse matrix methods; however, it is not fully adapted for QTL mapping association and linkage studies. In particular, two LMM features are lacking in the base version of lme4: the definition of random effects by custom covariance matrices; and parameter constraints, which are essential in advanced QTL models. Apart from applications in linkage studies of related individuals, such functionalities are of high interest for association studies in situations where multiple covariance matrices need to be modeled, a scenario not covered by many genome-wide association study (GWAS) software. RESULTS: To address the aforementioned limitations, we developed a new R package lme4qtl as an extension of lme4. First, lme4qtl contributes new models for genetic studies within a single tool integrated with lme4 and its companion packages. Second, lme4qtl offers a flexible framework for scenarios with multiple levels of relatedness and becomes efficient when covariance matrices are sparse. We showed the value of our package using real family-based data in the Genetic Analysis of Idiopathic Thrombophilia 2 (GAIT2) project. CONCLUSIONS: Our software lme4qtl enables QTL mapping models with a versatile structure of random effects and efficient computation for sparse covariances. lme4qtl is available at https://github.com/variani/lme4qtl .

UNLABELLED: : The open source environment R is one of the most widely used software for statistical computing. It provides a variety of applications including statistical genetics. Most of the powerful tools for quantitative genetic analyses are stand-alone free programs developed by researchers in academia. SOLAR is one of the standard software programs to perform linkage and association mappings of the quantitative trait loci (QTLs) in pedigrees of arbitrary size and complexity. solarius allows the user to exploit the variance component methods implemented in SOLAR. It automates such routine operations as formatting pedigree and phenotype data. It parses also the model output and contains summary and plotting functions for exploration of the results. In addition, solarius enables parallel computing of the linkage and association analyses that makes the calculation of genome-wide scans more efficient. AVAILABILITY AND IMPLEMENTATION: solarius is available on CRAN and on GitHub https://github.com/ugcd/solarius CONTACT: : [email protected].

MOTIVATION: Finding association between genetic variants and phenotypes related to disease has become an important vehicle for the study of complex disorders. In this context, multi-loci genetic association might unravel additional information when compared with single loci search. The main goal of this work is to propose a non-linear methodology based on information theory for finding combinatorial association between multi-SNPs and a given phenotype. RESULTS: The proposed methodology, called MISS (mutual information statistical significance), has been integrated jointly with a feature selection algorithm and has been tested on a synthetic dataset with a controlled phenotype and in the particular case of the F7 gene. The MISS methodology has been contrasted with a multiple linear regression (MLR) method used for genetic association in both, a population-based study and a sib-pairs analysis and with the maximum entropy conditional probability modelling (MECPM) method, which searches for predictive multi-locus interactions. Several sets of SNPs within the F7 gene region have been found to show a significant correlation with the FVII levels in blood. The proposed multi-site approach unveils combinations of SNPs that explain more significant information of the phenotype than their individual polymorphisms. MISS is able to find more correlations between SNPs and the phenotype than MLR and MECPM. Most of the marked SNPs appear in the literature as functional variants with real effect on the protein FVII levels in blood. AVAILABILITY: The code is available at http://sisbio.recerca.upc.edu/R/MISS_0.2.tar.gz

Finding association between genotypic differences and disease traits has become one of the main objectives in current genetic research. It has been published that some of the underlying factors in the dynamics of the coagulation process have a genetic compound, showing significant hereditability. This is the case of the Factor VII. In this work, we propose a method for selecting sets of Single Nucleotide Polymorphisms (SNPs) of the F7 gene that are significantly related with the phenotype (Factor VII levels). The methodology is applied to the sib pairs from the GAIT project sample. The method consists of an adapted Sequential Floating Feature Selection (SFFS) algorithm. This algorithm is applied with two relevance criteria, one linear and one non linear. The SNPs sets found with linear models are included in the sets found with non linear techniques. The results fit in with previous results in clinical area.