Francine Niyonsaba has become the first athlete to break a world record having identified herself as having a difference of sex development (DSD).
The middle-distance runner, from Burundi, broke the old 2,000 metres world record by more than two seconds in Zagreb, finishing in a time of 5:21.56.
Athletes with DSDs are ineligible to compete internationally over distances between 400m and 1600m unless they take medication to reduce their high levels of testosterone.
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DSD's have become an increasingly hot-button topic, particularly since the Court of Arbitration for Sport (CAS) rejected, in 2019, former Olympic 400m champion Caster Semenya's appeal against World Athletics' rules that allow them to restrict testosterone levels in female runners.
Niyonsaba won silver over 800m at the 2016 Olympics in Rio de Janeiro but has since been forced to step up in distance.
She won the Diamond League title over 5,000m and recorded the fifth-fastest time over 3,000m outdoors earlier this year.
The Burundian finished fifth over the former distance at Tokyo 2020.
There was further discussion of the DSD regulations after Namibia's Christine Mboma followed Olympic 200m silver with the Diamond League tile last week, in the process setting an Under-20 world record at the age of 18.

Francine Niyonsaba of Burundi celebrates winning the women's 2000m race during IAAF World Challenge Zagreb 2021 - 71st Boris Hanzekovic Memorial at University park

Image credit: Getty Images

Mboma prefers the 400m but cannot compete internationally in the one-lap race.
Her teammate Beatrice Masilingi was also blocked from competing over the distance at the Tokyo Olympics.
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