How no two people have the same sense of smell: Tiny DNA difference determines someone finds an aroma delicious or disgusting

• Researchers at Duke University, North Carolina, discovered there are almost a million variations on 400 smell receptors
  
• They found that a difference at the smallest level of DNA - one amino acid on one gene - can determine whether a person finds a given smell pleasant

By Sarah Griffiths

Published: 09:32 EST, 16 December 2013 | Updated: 09:36 EST, 16 December 2013

No two people smell scents the same way, which explains why some people find certain aromas appealing and others find the same smell stomach-churning.

U.S scientists have found that a difference at the smallest level of DNA - one amino acid on one gene - can determine whether a person finds a given smell pleasant.

They discovered there are almost a million variations on 400 smell receptors so that everyone smells things differently.

Psychologists from Belgium found that bad body odour is commonly associated with vulnerability, which triggers feelings of concern. This, in turn, leads other people to pity the person with the odour and treat them more favourably than others

Researchers at Duke University in Durham, North Carolina, said a different amino acid on the same gene in a friend's body could mean they find the an odour offensive that you find pleasant.

There are about 900,000 genetic variations on 400 smell receptors in our noses, according to the 1000 Genomes Project.

These receptors control the sensors that determine how we smell odours, so a given scent will activate a suite of receptors in the nose, creating a specific signal for the brain.

But Hiroaki Matsunami, associate professor of molecular genetics and microbiology at the university’s School of Medicine, said the receptors work differently for all of us.

‘There are many cases when you say you like the way something smells and other people don't. That's very common,’ he said.

Hiroaki Matsunami (pictured) led a team of scientists who systematically explored the triggers for specific odour receptors in the nose. The researchers found that no two people apparently smell things the same way

‘We found that individuals can be very different at the receptor levels, meaning that when we smell something, the receptors that are activated can be very different (from one person to the next) depending on your genome,’ Dr Matsunami said.

He explained that when comparing the receptors in any two people, they should be about 30 per cent different, but this figure is conservative.

While researchers have earlier identified the genes that encode for humans' odour receptors, it has been a mystery how the receptors are activated.

To determine what turns the receptors on and why certain smells appeal to different people, his team cloned more than 500 receptors each from 20 people that had slight variations of only one or two amino acids.

They then systematically subjected the molecules to different smells to see how they worked.

There are about 900,000 genetic variations on 400 smell receptors in our noses, according to the 1000 Genomes Project. These receptors control the sensors that determine how we smell odours, so a given scent will activate a suite of receptors in the nose, creating a specific signal for the brain

By exposing each receptor to a very small concentration of 73 aromas, such as vanillin (one of the chemical constituents of the aroma and taste of vanilla) or guaiacol, (an oily aromatic substance derived from wood creosote) the group was able to identify 27 receptors that had a significant response to at least one odorant.

This finding, published in the December issue of Nature Neuroscience, doubles the number of known odorant-activated receptors, bringing the number to 40.

Dr Matsunami said this research could have a big impact for fragrance, and food industries.

‘These manufacturers all want to know a rational way to produce new chemicals of interest, whether it's a new perfume or new-flavored ingredient, and right now there's no scientific basis for doing that,’ he said.

‘To do that, we need to know which receptors are being activated by certain chemicals and the consequences of those activations in terms of how we feel and smell.’

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