Ever imagined why it is so difficult to buy perfume for a loved one?
People experience odours in a completely different way, a new study has found.
Researchers from the Monell Center and collaborating institutions have found that as much as 30 per cent of the large array of human olfactory receptor differs between any two individuals.
This substantial variation is in turn reflected by variability in how each person perceives odours.
Humans have about 400 different types of specialised sensors, known as olfactory receptor proteins, that somehow work together to detect a large variety of odours.
"Understanding how this huge array of receptors encodes odours is a challenging task," said study lead author Joel Mainland, a molecular biologist at Monell.
"The activation pattern of these 400 receptors encodes both the intensity of an odour and the quality - for example, whether it smells like vanilla or smoke - for the tens of thousands of different odours that represent everything we smell," said Mainland.
The underlying amino acid sequence can vary slightly for each of the 400 receptor proteins, resulting in one or more variants for each of the receptors.
Each receptor variant responds to odours in a slightly different way and the variants are distributed across individuals such that nearly everyone has a unique combination of olfactory receptors.
To gain a better understanding of the extent of olfactory receptor variation and how this impacts human odour perception, Mainland and his collaborators used a combination of high-throughput assays to measure how single receptors and individual humans respond to odours.
The results provide a critical step towards understanding how olfactory receptors encode the intensity, pleasantness and quality of odour molecules.
The researchers first cloned 511 known variants of human olfactory receptors and embedded them in host cells that are easy to grow in the laboratory.
The next step was to measure whether each receptor variant responded to a panel of 73 different odour molecules. This process identified 28 receptor variants that responded to at least one of the odour molecules.
Researchers next examined the DNA of 16 olfactory receptor genes, discovering considerable variation within the genes for discrete receptors.
Using sophisticated mathematical modelling to extrapolate from these results, Mainland predicts that the olfactory receptors of any two individuals differ by about 30 per cent.
This means that for any two randomly chosen individuals, approximately 140 of their 400 olfactory receptors will differ in how they respond to odour molecules.
The study was published in the journal Nature Neuroscience.
