Humans have approximately 400 intact odorant receptors, but each individual has a unique set of genetic variations that lead to variation in olfactory perception. We used a heterologous assay to determine how often genetic polymorphisms in odorant receptors alter receptor function. We identified agonists for 18 odorant receptors and found that 63% of the odorant receptors we examined had polymorphisms that altered in vitro function. On average, two individuals differ functionally at over 30% of their odorant receptor alleles. To show that these in vitro results are relevant to olfactory perception, we verified that variations in OR10G4 genotype explain over 15% of the observed variation in perceived intensity and over 10% of the observed variation in perceived valence for the high affinity in vitro agonist guaiacol, but do not explain phenotypic variation for the lower affinity agonists vanillin and ethyl vanillin.

Humans use a family of more than 400 olfactory receptors (ORs) to detect odors, but there is currently no model that can predict olfactory perception from receptor activity patterns. Genetic variation in human ORs is abundant and alters receptor function, allowing us to examine the relationship between receptor function and perception. We sequenced the OR repertoire in 332 individuals and examined how genetic variation affected 276 olfactory phenotypes, including the perceived intensity and pleasantness of 68 odorants at two concentrations, detection thresholds of three odorants, and general olfactory acuity. Genetic variation in a single OR was frequently associated with changes in odorant perception, and we validated 10 cases in which in vitro OR function correlated with in vivo odorant perception using a functional assay. In 8 of these 10 cases, reduced receptor function was associated with reduced intensity perception. In addition, we used participant genotypes to quantify genetic ancestry and found that, in combination with single OR genotype, age, and gender, we can explain between 10% and 20% of the perceptual variation in 15 olfactory phenotypes, highlighting the importance of single OR genotype, ancestry, and demographic factors in the variation of olfactory perception. olfaction | genetic variation | human genome | odor intensity | ancestry U nderstanding how the olfactory system detects odorants and translates their features into perceptual information is one of the fundamental questions in olfaction. Although early color vision researchers were unable to directly observe receptor responses, perceptual deficits caused by genetic variation (i.e., color blindness) helped show that color vision is mediated by three receptors responding to different wavelengths of light (1, 2). Guillot (3), and then Amoore (4), extended this idea to olfaction and proposed that cataloging specific anosmias (the inability to perceive a particular odorant) may provide similar clues linking genes and perception. Early applications of this idea failed, presumably because olfaction relies on hundreds of receptors, and without direct observation of their responses, psychophysical tests could not untangle the fundamental rules of odor coding. However, with the advent of next-generation genome sequencing to profile olfactory receptor (OR) genes and cell-based assays to identify ligands for ORs, receptor variation can now be matched to individuals and receptor responses can be directly observed.Humans have approximately 400 OR genes that are intact in at least part of the population, but individuals have different repertoires of pseudogenes, copy number variations, and single nucleotide polymorphisms (SNPs) that can alter receptor responses (5-7). While nonfunctional genes are rare in the genome (on average approximately 100 heterozygous and 20 homozygous pseudogenes in an individual), they are significantly enriched in OR genes (8). This provides a useful set of "natural knockouts" to examine the role of a single OR in olfactory pe...

RNA interference (RNAi) is a process that can target intracellular RNAs for degradation in a highly sequence specific manner, making it a powerful tool that is being pursued in both research and therapeutic applications. Hepatitis B virus (HBV) is a serious public health problem in need of better treatment options, and aspects of its life cycle make it an excellent target for RNAi-based therapeutics. We have designed a vector that expresses interfering RNAs that target HBV transcripts, including both viral RNA replicative intermediates and mRNAs encoding viral proteins. Our vector design incorporates many features of endogenous microRNA (miRNA) gene organization that are proving useful for the development of reagents for RNAi. In particular, our vector contains an RNA pol II driven gene cassette that leads to tissue specific expression and efficient processing of multiple interfering RNAs from a single transcript, without the co-expression of any protein product. This vector shows potent silencing of HBV targets in cell culture models of HBV infection. The vector design will be applicable to silencing of additional cellular or disease-related genes.

The human olfactory receptor repertoire is characterized by an abundance of genetic variation that affects receptor response, but the perceptual effects of this variation are unclear. To address this issue, we sequenced the OR repertoire in 332 individuals and examined the relationship between genetic variation and 276 olfactory phenotypes, including the perceived intensity and pleasantness of 68 odorants at two concentrations, detection thresholds of three odorants, and general olfactory acuity. Genetic variation in a single OR frequently associated with odorant perception, and we validated 10 cases in which in vitro OR function correlated with in vivo odorant perception using a functional assay. This more than doubles the published examples of this phenomenon. For eight of these 10 cases, reduced receptor function associated with reduced intensity perception. In addition, we used participant genotypes to quantify genetic ancestry and found that, in combination with single OR genotype, age and gender, we can explain between 10 and 20% of the perceptual variation in 15 olfactory phenotypes, highlighting the importance of single OR genotype, ancestry, and demographic factors in variation of olfactory perception.