Sisters Caitlin and Grace Leggett from Cardiff made a shocking discovery after believing they were fraternal twins for years—they’re actually identical! This revelation came after Caitlin, 23, was diagnosed with acute myeloid leukaemia (AML), and Grace was set to donate stem cells to help her sibling. However, doctors found they were identical twins, which meant Grace couldn’t be a donor because their DNA was too similar!
The sisters have always been close, sharing everything from hobbies to university days. Growing up as “peas in a pod,” they always assumed they were dizygotic, formed from separate eggs. But Caitlin’s diagnosis turned life upside down, and during the testing process, doctors realised the truth: they’re monozygotic twins, formed from a single fertilised egg that split into two.
This discovery made the twins feel cooler, but it complicated Caitlin’s treatment. Grace’s identical DNA meant she couldn’t donate her stem cells, as Caitlin’s body needed to recognise the cells as foreign to successfully fight the cancer.
Caitlin faced a rollercoaster of treatments, including chemotherapy and a clinical trial, before receiving a stem cell transplant from an anonymous donor in December 2025. Despite some challenges, Caitlin’s transplant was a success, and she’s continuing her fight with positive spirits.
Now, both Caitlin and Grace are calling on everyone to consider becoming stem cell donors. It’s quick, easy, and it can save lives. They stress the importance of having donors available because cancer can strike anyone, anytime. As Grace puts it, “It takes maybe six hours maximum to donate and then for someone else, it changes their life.”
Find out more about becoming a stem cell donor in the UK by visiting dkms.org.uk. It’s a simple step with a huge impact—because you never know when it might be your chance to offer the gift of life.