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For years, scientists have known that people with type O blood are twice
as likely to develop stomach ulcers as those with other blood types. What
they have not known is why. Now scientists in the US and Sweden have come
up with a possible explanation: the bacterium believed to cause ulcers (Helicobacter
pylori) may attach itself to the stomach’s lining by a string of sugars
found only in people type O blood.

Both ulcers and gastritis are linked to H. pylori, which, in developed
countries, lurks in the stomachs of more than 60 per cent of adults by
the time they are 60. The complaints develop when the bacterium works
its way through the stomach’s protective mucus and onto the stomach’s inner
lining. The bacteria stick to the lining’s epithelial cells, releasing toxins
and causing inflammation that damages the tissue and irritate the stomach.
H. pylori infection is also linked to stomach cancer.

Previously, scientists have found that the bacterium binds to a sugar
called sialic acid, which is found on the surfaces of many cells and also
in the stomach’s protective mucus.

Steffan Normark and colleagues at Washington University School of Medicine
in St Louis and the University of Goteborg in Sweden have found another
way for the bacterium to stick to stomach cells – via an arrangement of
sugars known as the Lewis to the power of b blood group antigen. But they
have found that H. pylori will not stick to any old Lewisb antigen – only
the form that is generally found in people with type O blood.

‘It’s an interesting observation,’ says Martin Blaser, a microbiologist
at Vanderbilt University School of Medicine, in Tennessee. But the Lewis
to the power of b antigen cannot be the only factor, he points out, because
those with type O blood are only twice as likely to come down with ulcers,
instead of many times more likely. Sticking to the stomach wall is not everything,
he says.

If the Lewis to the power of b antigen theory holds up, it might lead
to new treatments for ulcers and gastritis, says Thomas Boren, a colleague
of Normark’s. Perhaps scientists could design new, improved drugs that bind
H. pylori even tighter, ‘pulling’ the bacterium off the stomach’s cells
and flushing it out of the body.

Breast milk also contains Lewisb antigen, says Boren, which might also
inhibit binding to the stomach wall. ‘If the babies drink their mother’s
milk maybe they are protected from getting infected by the bacterium,’ he
says. ‘It’s speculation – but I think there could be something to it.’