Genotype influence in responses to therapy for atrial fibrillation

Polymorphism in INSR Locus Modifies Risk of Atrial Fibrillation in Patients on Thyroid Hormone Replacement Therapy

Aims

Atrial fibrillation (AF) is a risk for patients receiving thyroid hormone replacement therapy. No published work has focused on pharmacogenetics relevant to thyroid dysfunction and AF risk. We aimed to assess the effect of L-thyroxine on AF risk stratified by a variation in a candidate gene.

Methods and Results

A retrospective follow-up study was done among European Caucasian patients from the Genetics of Diabetes Audit and Research in Tayside Scotland cohort (Scotland, United Kingdom). Linked data on biochemistry, prescribing, hospital admissions, demographics, and genetic biobank were used to ascertain patients on L-thyroxine and diagnosis of AF. A GWAS-identified insulin receptor-INSR locus (rs4804416) was the candidate gene. Cox survival models and sensitivity analyses by taking competing risk of death into account were used. Replication was performed in additional sample (The Genetics of Scottish Health Research register, GoSHARE), and meta-analyses across the results of the study and replication cohorts were done. We analyzed 962 exposed to L-thyroxine and 5,840 unexposed patients who were rs4804416 genotyped. The rarer G/G genotype was present in 18% of the study population. The total follow-up was up to 20 years, and there was a significant increased AF risk for patients homozygous carriers of the G allele exposed to L-thyroxine (RHR = 2.35, P = 1.6e-02). The adjusted increased risk was highest within the first 3 years of exposure (RHR = 9.10, P = 8.5e-04). Sensitivity analysis yielded similar results. Effects were replicated in GoSHARE (n = 3,190).

Conclusion

Homozygous G/G genotype at the INSR locus (rs4804416) is associated with an increased risk of AF in patients on L-thyroxine, independent of serum of free thyroxine and thyroid-stimulating hormone serum concentrations.

Personalized warfarin treatment based on the PITX2 single nucleotide polymorphism rs6843082

OBJECTIVE

To explore the effect of PITX2 gene rs6843082 single nucleotide polymorphism on the efficacy and adverse reactions of warfarin in patients with atrial fibrillation and hypertension, and to provide a theoretical basis for individualized warfarin treatment.

METHODS

Data on 97 patients with atrial fibrillation and hypertension treated in our hospital were collected from September, 2018 to December, 2019. PCR and SNP genotyping techniques were used to measure the genotype at the rs6843082 locus (pituitary homeobox 2, PITX2) using DNA from the peripheral blood cells of all patients. We compared the efficacy of warfarin and the incidence of adverse reactions in patients of different genotypes.

RESULTS

(1) Among 97 subjects, 58 cases (59.79%), 32 cases (32.99%) and 7 cases (7.22%) of PITX2 (rs6843082) genotypes GG, GA and AA were identified respectively. The G and A allele frequencies were 76.29% and 23.71%, respectively. (2) After all patients took warfarin to achieve the standard, the GA group and AA group's time to achieve the standard was significantly longer than that of the GG group (P<0.05). The difference was not statistically significant among groups (P>0.05). Compared with the GG group, the maintenance dose of the AA group was increased (P<0.05). (3) Compared with the GG and the GA group, the probability of bleeding events was higher in the AA group (P<0.05). (4) There was no difference in left ventricular end diastolic volume (LVEDV) and left ventricular end systolic volume (LVESV) group among GG, GA and AA groups (P>0.05). Compared with the GG group, left ventricular ejection fraction (LVEF) of the AA group was significantly reduced (P<0.05). (5) The mortality rates of the GG, GA, and AA groups were 15.51%, 12.50% and 22.57%, respectively, at the end of 120 d follow-up.

CONCLUSION

Our findings show that rs6843082 SNP leads to the warfarin dose response differences that were observed in patients with atrial fibrillation and hypertension. Genotyping patients for rs6843082 before initiating warfarin treatment may optimize the treatment response and reduce bleeding incidence.

Atrial Fibrillation Mechanisms and Implications for Catheter Ablation

AF is a heterogeneous rhythm disorder that is related to a wide spectrum of etiologies and has broad clinical presentations. Mechanisms underlying AF are complex and remain incompletely understood despite extensive research. They associate interactions between triggers, substrate and modulators including ionic and anatomic remodeling, genetic predisposition and neuro-humoral contributors. The pulmonary veins play a key role in the pathogenesis of AF and their isolation is associated to high rates of AF freedom in patients with paroxysmal AF. However, ablation of persistent AF remains less effective, mainly limited by the difficulty to identify the sources sustaining AF. Many theories were advanced to explain the perpetuation of this form of AF, ranging from a single localized focal and reentrant source to diffuse bi-atrial multiple wavelets. Translating these mechanisms to the clinical practice remains challenging and limited by the spatio-temporal resolution of the mapping techniques. AF is driven by focal or reentrant activities that are initially clustered in a relatively limited atrial surface then disseminate everywhere in both atria. Evidence for structural remodeling, mainly represented by atrial fibrosis suggests that reentrant activities using anatomical substrate are the key mechanism sustaining AF. These reentries can be endocardial, epicardial, and intramural which makes them less accessible for mapping and for ablation. Subsequently, early interventions before irreversible remodeling are of major importance. Circumferential pulmonary vein isolation remains the cornerstone of the treatment of AF, regardless of the AF form and of the AF duration. No ablation strategy consistently demonstrated superiority to pulmonary vein isolation in preventing long term recurrences of atrial arrhythmias. Further research that allows accurate identification of the mechanisms underlying AF and efficient ablation should improve the results of PsAF ablation.

Genetics of atrial fibrillation

PURPOSE OF REVIEW

Atrial fibrillation is a common cardiac arrhythmia with a high morbidity and mortality affecting 34 million worldwide. Current therapies are inadequate and often fail to directly address molecular mechanisms of the disease. In this review, we will provide an overview of recent advances in our understanding of the genetic underpinnings of atrial fibrillation.

RECENT FINDINGS

Large-scale genetic association studies have more than doubled the number of genetic loci associated with atrial fibrillation during the last year. Studies examining how genes at or near these loci can affect the pathogenesis of atrial fibrillation are ongoing in cellular, animal, and computational models. In addition, several recent clinical studies have also demonstrated that variants at these loci can aid in risk stratification of patients.

SUMMARY

There are now over 30 genetic loci associated with atrial fibrillation. A better understanding of how these loci relate to disease pathogenesis may provide insight into novel therapeutic targets and ultimately lead to improved clinical care.