Adjusting for principal components can induce collider bias in genome-wide association studies

PTPN2 and Leukopenia in Individuals With Normal TPMT and NUDT15 Metabolizer Status Taking Azathioprine

Leukopenia is a common dose-dependent side effect of azathioprine, often leading to drug discontinuation. Variants in TPMT and NUDT15 are associated with azathioprine-induced leukopenia but only explain 25% of cases. Thus, we aimed to identify novel genetic risk factors among TPMT and NUDT15 normal metabolizers through a genome-wide association study (GWAS). Using BioVU, Vanderbilt's electronic health record linked to genetic data, we assembled a discovery cohort of new users of azathioprine. The analysis was conducted in 1184 new users of azathioprine who had no history of prior thiopurine use or an organ transplant. A replication cohort of 521 patients was derived from All of Us, an NIH-funded project that links healthcare data and genetics. The GWAS was adjusted for sex, age, indication (inflammatory bowel disease, systemic lupus erythematosus, other autoimmune condition, or unknown), concurrent use of xanthine oxidase inhibitors (allopurinol or febuxostat) or immunosuppressants, prior TPMT or NUDT15 testing, and 10 principal components of ancestry. In BioVU, 65% of patients were female with a median age of 44 [IQR: 30, 57] and 125 patients developed leukopenia. In All of Us, 69% were female with a median age of 51 [36, 61], and 44 patients developed leukopenia. An intronic variant in PTPN2, rs11664064, reached genome-wide significance in BioVU (OR = 3.61; p = 1.96E-8) and replicated in All of Us (OR = 2.42, p = 0.039). Our finding suggests an association between rs11664064 in PTPN2 and azathioprine-induced leukopenia. PTPN2 plays a role in immune cell development and differentiation, providing a plausible mechanism for this association.

Reproducibility of genetic risk factors identified for long COVID using combinatorial analysis across US and UK patient cohorts with diverse ancestries

BACKGROUND

Long COVID is a major public health burden causing a diverse array of debilitating symptoms in tens of millions of patients globally. In spite of this overwhelming disease prevalence, staggering cost, severe impact on patients' lives and intense global research efforts, study of the disease has proved challenging due to its complexity. Genome-wide association studies (GWAS) have identified only four loci potentially associated with the disease, although these results did not statistically replicate between studies. A previous combinatorial analysis study identified a total of 73 genes that were highly associated with two long COVID cohorts in the predominantly (> 91%) white European ancestry Sano GOLD population, and we sought to reproduce these findings in the independent and ancestrally more diverse All of Us (AoU) population.

METHODS

We assessed the reproducibility of the 5343 long COVID disease signatures from the original study in the AoU population. Because the very small population sizes provide very limited power to replicate findings, we initially tested whether we observed a statistically significant enrichment of the Sano GOLD disease signatures that are also positively correlated with long COVID in the AoU cohort after controlling for population substructure.

RESULTS

For the Sano GOLD disease signatures that have a case frequency greater than 5% in AoU, we consistently observed a significant enrichment (77-83%, p < 0.01) of signatures that are also positively associated with long COVID in the AoU cohort. These encompassed 92% of the genes identified in the original study. At least five of the disease signatures found in Sano GOLD were also shown to be individually significantly associated with increased long COVID prevalence in the AoU population. Rates of signature reproducibility are strongest among self-identified white patients, but we also observe significant enrichment of reproducing disease associations in self-identified black/African-American and Hispanic/Latino cohorts. Signatures associated with 11 out of the 13 drug repurposing candidates identified in the original Sano GOLD study were reproduced in this study.

CONCLUSION

These results demonstrate the reproducibility of long COVID disease signal found by combinatorial analysis, broadly validating the results of the original analysis. They provide compelling evidence for a much broader array of genetic associations with long COVID than previously identified through traditional GWAS studies. This strongly supports the hypothesis that genetic factors play a critical role in determining an individual's susceptibility to long COVID following recovery from acute SARS-CoV-2 infection. It also lends weight to the drug repurposing candidates identified in the original analysis. Together these results may help to stimulate much needed new precision medicine approaches to more effectively diagnose and treat the disease. This is also the first reproduction of long COVID genetic associations across multiple populations with substantially different ancestry distributions. Given the high reproducibility rate across diverse populations, these findings may have broader clinical application and promote better health equity. We hope that this will provide confidence to explore some of these mechanisms and drug targets and help advance research into novel ways to diagnose the disease and accelerate the discovery and selection of better therapeutic options, both in the form of newly discovered drugs and/or the immediate prioritization of coordinated investigations into the efficacy of repurposed drug candidates.

Validation of Polymorphisms Associated with the Immune Response After Vaccination Against Porcine Reproductive and Respiratory Syndrome Virus in Yorkshire Gilts

Porcine respiratory and reproductive syndrome is a viral disease that impacts the health and profitability of swine farms, largely due to significant variation in the vaccination response. The objective was to identify and validate molecular markers associated with the antibody response in gilts following vaccination against the PRRSV. The study included one hundred (n = 100) 6-month-old Yorkshire gilts that were negative for the PRRSV. Gilts were randomly assigned to one of two treatments, PRRS-vaccinated (n = 75) and control (n = 25) groups. Blood samples collected on day 21 were analyzed to evaluate the antibody response, as indicated by the sample-to-positive (S/P) ratio, to the PRRSV following vaccination. DNA was extracted and genotyped using a low-density chip containing 10,000 single nucleotide polymorphisms (SNPs). A genome-wide association study (GWAS) was conducted to identify candidate SNPs associated with the S/P ratio, which were validated in two independent gilt populations (n = 226). The SNPs rs707264998, rs708860811, and rs81358818 in the genes RNF144B, XKR9, and BMAL1, respectively, were significantly associated (p < 0.01) with the S/P ratio and demonstrated an additive effect. In conclusion, three SNPs are proposed as candidate markers for an enhanced immune response to vaccination against the PRRSV and may be beneficial in genetic selection programs.