Evolutionary evidence of the effect of rare variants on disease etiology

Gorlov IP, Gorlova OY, Frazier ML, Spitz MR, Amos CI. Evolutionary evidence of the effect of rare variants on disease etiology. The common disease/common variant hypothesis has been popular for describing the genetic architecture of common human diseases for several years. According to the originally stated hypothesis, one or a few common genetic variants with a large effect size control the risk of common diseases. A growing body of evidence, however, suggests that rare single‐nucleotide polymorphisms (SNPs), i.e. those with a minor allele frequency of less than 5%, are also an important component of the genetic architecture of common human diseases. In this study, we analyzed the relevance of rare SNPs to the risk of common diseases from an evolutionary perspective and found that rare SNPs are more likely than common SNPs to be functional and tend to have a stronger effect size than do common SNPs. This observation, and the fact that most of the SNPs in the human genome are rare, suggests that rare SNPs are a crucial element of the genetic architecture of common human diseases. We propose that the next generation of genomic studies should focus on analyzing rare SNPs. Further, targeting patients with a family history of the disease, an extreme phenotype, or early disease onset may facilitate the detection of risk‐associated rare SNPs.     

An initial watch and wait approach is a valid strategy for selected patients with newly diagnosed metastatic colorectal cancer

BackgroundA range of treatments are available for patients with metastatic colorectal cancer (mCRC). An initial period without active treatment, a ‘watch and wait approach’, is variably employed in routine practice; however, there is no data to support this approach.Patients and methodsWe prospectively collected data regarding clinician treatment recommendations for patients with newly diagnosed mCRC in addition to subsequent treatment and outcomes. Follow-up and management was according to standard protocols.ResultsSeven hundred and thirty-six patients (59.1% male, 40.9% female) with mCRC (January 2003–December 2010) were analysed; the median age was 67.9 years (range 26.2–95.5). Three hundred and seventy-seven patients (51.2%) received immediate chemotherapy. For 133 (18.1%), treatment was considered inappropriate. 34 patients (4.6%) declined therapy. For 192 (26.1%), a watch and wait policy was adopted and 168 (87.5%) of these received treatment, at a median of 3.7 months (range 2–35 months) from diagnosis. Compared with patients immediately treated, the number receiving all active chemotherapy agents (30.4 versus 39.3%) was similar and median survival (27 versus 17 months, P = 0.0008) was superior.ConclusionsOur study demonstrates that a substantial minority of patients underwent an initial watch and wait approach. Ultimately, they received a similar treatment exposure to patients treated immediately and the survival outcomes were not compromised.     

Validation of Methods to Control for Immortal Time Bias in a Pharmacoepidemiologic Analysis of Renin–Angiotensin System Inhibitors in Type 2 Diabetes

Background

Pharmacoepidemiologic analysis can confirm whether drug efficacy in a randomized controlled trial (RCT) translates to effectiveness in real settings. We examined methods used to control for immortal time bias in an analysis of renin–angiotensin system (RAS) inhibitors as the reference cardioprotective drug.

Methods

We analyzed data from 3928 patients with type 2 diabetes who were recruited into the Hong Kong Diabetes Registry between 1996 and 2005 and followed up to July 30, 2005. Different Cox models were used to obtain hazard ratios (HRs) for cardiovascular disease (CVD) associated with RAS inhibitors. These HRs were then compared to the HR of 0.92 reported in a recent meta-analysis of RCTs.

Results

During a median follow-up period of 5.45 years, 7.23% (n = 284) patients developed CVD and 38.7% (n = 1519) were started on RAS inhibitors, with 39.1% of immortal time among the users. In multivariable analysis, time-dependent drug-exposure Cox models and Cox models that moved immortal time from users to nonusers both severely inflated the HR, and time-fixed models that included immortal time deflated the HR. Use of time-fixed Cox models that excluded immortal time resulted in a HR of only 0.89 (95% CI, 0.68–1.17) for CVD associated with RAS inhibitors, which is closer to the values reported in RCTs.

Conclusions

In pharmacoepidemiologic analysis, time-dependent drug exposure models and models that move immortal time from users to nonusers may introduce substantial bias in investigations of the effects of RAS inhibitors on CVD in type 2 diabetes.Key words: cardiovascular disease, immortal time bias, renin–angiotensin system inhibitors, time-dependent Cox model, cancer, type 2 diabetes