Examining complete gene knockouts within a viable organism can inform on gene function. We sequenced the exomes of 3,222 British Pakistani-heritage adults with high parental relatedness, discovering 1,111 rare-variant homozygous genotypes with predicted loss of gene function (knockouts) in 781 genes. We observed 13.7% fewer than expected homozygous knockout genotypes, implying an average load of 1.6 recessive-lethal-equivalent LOF variants per adult. Linking genetic data to lifelong health records, knockouts were not associated with clinical consultation or prescription rate. In this dataset we identified a healthy PRDM9 knockout mother, and performed phased genome sequencing on her, her child and controls, which showed meiotic recombination sites localised away from PRDM9-dependent hotspots. Thus, natural LOF variants inform upon essential genetic loci, and demonstrate PRDM9 redundancy in humans.

Data from many preclinical studies, including those using cellular models of colorectal, gastric, gastro-oesophageal and gastro-oesophageal junction cancers, indicate that the hepatocyte growth factor (HGF)-hepatocyte growth factor receptor (c-MET) pathway is vital for the growth, survival and invasive potential of gastrointestinal cancers. Following the availability of data from these various studies, and data on c-MET expression as a biomarker that indicates a poor prognosis in patients with gastrointestinal cancer and increased c-MET expression, inhibitors targeting this pathway have entered the clinic in the past decade. However, the design of clinical trials that incorporate the use of HGF/c-MET inhibitors in their most appropriate genetic and molecular context remains crucial. Recognizing and responding to this challenge, the European Commission funded Framework 7 MErCuRIC programme is running a biomarker-enriched clinical trial investigating the efficacy of combined c-MET/MEK inhibition in patients with RAS-mutant or RAS-wild-type metastatic colorectal cancer with aberrant c-MET expression. The design of this trial enables the continued refinement of the predictive biomarker and co-development of companion diagnostics. In this Review, we focus on advances in our understanding of inhibition of the HGF/c-MET pathway in patients with gastro-intestinal cancers, the prominent challenges facing the clinical translation and implementation of agents targeting HGF/c-MET, and discuss the various efforts, and associated obstacles to the discovery and validation of biomarkers that will enable patient stratification in this context.

Abstract:Complete gene knockouts are highly informative about gene function. We exome sequenced 3,222 British Pakistani heritage adults with high parental relatedness, discovering 1,111 rare variant homozygous likely loss of function (rhLOF) genotypes predicted to disrupt (knockout) 781 genes. Based on depletion of rhLOF genotypes, we estimate that 13.6% of knockouts are incompatible with adult life, finding on average 1.6 heterozygous recessive lethal LOF variants per adult. Linking to lifelong health records, we observed no association of rhLOF genotypes with prescription or doctor consultation rate, and no disease related phenotypes in 33 of 42 individuals with rhLOF genotypes in recessive Mendelian disease genes. Phased genome sequencing of a healthy PRDM9 knockout mother, her child and controls, showed meiotic recombination sites localised away from PRDM9 dependent hotspots, demonstrating PRDM9 redundancy in humans. Main Text:The study of gene function by correlating genotype with phenotype has provided profound biological insights for several decades. In particular, complete gene knockouts, typically caused by homozygous loss of function (LOF) genotypes, have been used to identify the function of many genes, predominantly through studies in model organisms and of severe Mendelian inherited diseases in humans. However, information on the consequences of knocking out most genes in humans is still missing. Naturally occurring complete gene knockouts, whilst exceptional in outbred populations, offer the opportunity to study directly the lifelong effects of systemic gene inactivation in a living human. They provide a key entry point into human biology that can then be tested in other systems, and can lead to direct validation of specific biological hypotheses. The first large survey of LOF variants in adult humans demonstrated ~100 predicted LOF genotypes per individual, describing around ~20 genes carrying homozygous predicted LOF alleles and hence likely completely inactivated(1). As expected almost all these homozygous genotypes were common (allele frequency) variants, and were concentrated in genes likely to have weak or neutral effects on fitness and health, for instance olfactory receptors. In contrast, rare predicted LOF genotypes in these outbred . CC-BY-NC-ND 4.0 International license peer-reviewed) is the author/funder. It is made available under a The copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/031641 doi: bioRxiv preprint first posted online Nov. 14, 2015; samples were usually heterozygous and thus of uncertain overall impact on gene function. Several approaches have been described recently to identify naturally occurring human knockouts. A large exome sequencing aggregation study (ExAC), of predominantly outbred individuals, identified 1,775 genes with homozygous predicted LOF genotypes in 60,706 individuals(2). In population isolates, 1,171 genes with complete predicted LOF were identified in 104,220 Icelandic individuals(3), and modest enrichment for homozygou...