The Economist - USA (2020-02-15)

68 TheEconomistFebruary 15th 2020

1

G

enes cantell tales about you, from

who your ancestors were to how likely

you are to develop a range of diseases. And

it seems probable that in the future they

will tell more: your personality type, per-

haps, or your intelligence. For these rea-

sons, many countries have laws limiting

what use employers and insurance compa-

nies can make of such information. Ameri-

ca, for example, has the Genetic Informa-

tion Nondiscrimination Act, which makes

it illegal for health insurers and employers

to use genetic information to discriminate

against customers and employees.

There is much, however, that genes can-

not reveal. They are blind to what you eat,

how you exercise, how safe the place you

live in is, how you unwind at the end of the

day and which god you worship. Just as

well, you might think, considering how

easy it is to obtain samples of dnafrom sa-

liva, sweat or hair, and how cheap it is be-

coming to analyse such samples. But it is

not just dnathat people scatter to the wind

as they go about their business. They shed a

whole range of other chemicals as well, in

their breath, their urine, their faeces and

their sweat. Collectively, and somewhat in-

accurately, these molecules are referred to

as metabolites. Some truly are the products

of metabolic activity within people’s bo-

dies. Others are substances an individual

has come into contact with, or consumed

or inhaled. All, though, carry information

of one sort or another.

Blood, tears, sweat and toil

Until recently this did not matter much, for

two reasons. One was that, in practice, tak-

ing samples for analysis required either vo-

luntary collaboration or legal duress. It

could not be done clandestinely. The other

was that interpreting the complicated pat-

terns of metabolites is hard. But both of

these obstacles are now being overcome.

The most common way of analysing

metabolite content is gas chromatography-

mass spectrometry. This technique sorts

molecules by their weight, producing a

pattern of peaks that correspond to differ-

ent substances. But the same weight can be

shared by many molecules, so the results

may be ambiguous. Nor, even if a molecule

can be identified unambiguously, is its

wider significance always obvious to a par-

ticular investigator.

There are, however, a lot of information

sources out there, in the form of publicly

available metabolite databases. And last

year a team led by Pieter Dorrestein of Uni-

versity of California, San Diego, invented a

way, which they call a metabolite search

engine, of linking them up so that a sample

can be compared simultaneously with the

contents of all of them.

The databases themselves are getting

better, too. According to Dr Dorrestein, re-

searchers in the field were able, as recently

as four years ago, to identify only 2% of the

metabolites found in samples. Today, that

has increased to 6% and is climbing quick-

ly. “It is reasonable”, he says, “to assume

that in another four years we will be able to

annotate 20% of the molecular signatures

that we encounter, based on the advances

that are being made.”

Another area of progress is the type, size

and state of preservation of samples that

can be interrogated. No longer are blood,

urine or breath required. Sweat, tears, sali-

Metabolites and you

Shed-loads of chemicals

People leave molecular wakes that may give away their secrets

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