Scientists have discovered a new set of blood groups

The unborn baby was in trouble. The mother’s doctors, at a British hospital, knew there was something wrong with the fetus’s blood, so they decided to perform an emergency cesarean section many weeks before the baby was due. But despite this, and subsequent blood transfusions, the baby suffered a brain hemorrhage with devastating consequences. It sadly passed away.

It was not clear why the bleeding had happened. But there was a clue in the mother’s blood where doctors had noticed strange antibodies. Sometime later, as the medics were trying to find out more about them, a sample of the mother’s blood arrived at a lab in Bristol run by researchers who study blood groups.

They made a surprising discovery: The woman’s blood was of an extremely rare type, which made her baby’s blood potentially incompatible with hers. It’s possible this prompted her immune system to produce antibodies against her baby’s blood — antibodies that then crossed the placenta and harm her child, ultimately leading to loss. It may seem unlikely that such a thing could happen, but many decades ago, before doctors had a better understanding of blood types, it was much more common.

By studying the mother’s blood sample, along with a number of others, scientists were able to figure out exactly what made her blood different, and in the process confirmed a new set of blood groupings – the “Er” system, the 44th that must be described.

You are probably familiar with the four main blood types: A, B, O and AB. But this is not the only blood classification system. There are many ways to group red blood cells based on differences in the sugars or proteins that coat their surface, known as antigens. The grouping systems work simultaneously, so your blood can be classified into each – for example, it could be type O in the ABO system, positive (instead of negative) under the Rhesus system, and so on.

Due to differences in antigens, when a person receives incompatible blood from a donor, the recipient’s immune system can detect those antigens as foreign and react against them. This can be very dangerous and so donated blood should be an appropriate match if someone is transfused.

On average, one new blood classification system has been described by researchers every year for the past decade. These newer systems tend to involve blood types that are mind-bogglingly rare, but for those touched by them, knowing they have such blood can be life-saving. This is the story of how scientists unraveled the mystery of the newest blood system — and why it matters.

It was back in 1982 that researchers first described an unusual antibody in a blood sample that indicated the existence of this mysterious blood group. The scientists couldn’t go much further at the time, but they knew the antibody was a clue pointing to an unknown molecule or structure that prompted the person’s immune system to generate it.

In the years that followed, more people with these unusual antibodies showed up, but only occasionally. In general, these people surfaced thanks to blood tests that contained the mysterious and rare antibodies. Finally, Nicole Thornton and her colleagues at NHS Blood and Transplant in the UK decided to investigate what might be behind the antibodies. “We’re working on rare cases,” she says. “It starts with a patient with a problem we’re trying to solve.”

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