Scents and sense ability: genes may influence perception of smell

Whether a smell strikes you as fragrant or fetid — or if you
even notice it at all — may be influenced by your genes, according to a pair of
studies.

Four chemical compounds commonly found in foods are
associated with specific areas of the genome. Researchers from the New Zealand Institute for Plant and Food
Research uncovered genetic
differences predicting a person's ability to sniff out malt, apples, blue
cheese and violets.

The team further probed the compound underlying a violet's
aroma — β-ionone — in a separate
study. They uncovered a mutation in a single gene that can affect people's ability to detect β-ionone
in food and beverages.

'This might mean that when people sit down to eat a meal,
they each experience it in their own personalised way', says Dr Jeremy McRae,
who was involved in both studies.

The researchers tested how sensitive 187 people were to ten
chemical compounds. Participants chose between three water-filled wine glasses,
one of which also contained one type of smelly molecule. Participants had to
select the odd one out: the aromatic glass.

The team then looked for variations in the participants' genomes linked to their
abilities to smell each of the ten odours. The genome-wide association study (GWAS) highlighted
regions of DNA statistically associated with four of the compounds. These
regions were located within or near clusters of odorant receptor genes.

'We were surprised how many odours had genes associated with
them. If this extends to other odours, then we might expect everyone to have
their own unique set of smells that they are sensitive to', said McRae.

A separate GWAS analysis found that
a change in a single letter in the odorant receptor gene OR5A1 affected
people's ability to distinguish β-ionone. With one version of the gene,
participants were more likely to pick up β-ionone's 'pleasant floral note'. People
with another mutation found the scent 'sour' or 'pungent'.

OR5A1 is one of nearly 400 odorant, or olfactory,
receptor genes present in humans. These genes produce proteins that sit on sensory
nerves in the nose, catching different molecules from the air and signalling
the brain. These signals lead to the perception of smell.

Dr Richard
Newcomb, senior author on both studies, told
Nature: 'All of these genes are on different chromosomes, acting
independently, so all these different people — even just for these four
compounds — are having totally different experiences of the chemical world
through their sense of smell'.