Twin sisters Caitlin and Grace Leggett, 23, from Cardiff, have discovered they are identical twins after Caitlin was diagnosed with acute myeloid leukaemia. The pair had always believed they were fraternal, but genetic testing revealed they are monozygotic.
Caitlin was diagnosed with AML in April 2025 after developing a persistent rash. She underwent chemotherapy and was scheduled for a stem cell transplant, with Grace initially identified as a suitable donor. However, further tests showed the sisters are identical, meaning Grace's stem cells could not be used as the transplant relies on the recipient's body recognising the donor cells as foreign.
Doctors explained that with near-identical DNA, the transplant would not be effective. Caitlin's transplant was postponed, and she participated in a clinical trial in Manchester to treat leukaemia that had spread to her skin. The trial was successful, and a new transplant date has been set.
Grace said: 'I always wished I was an identical twin – I liked being a twin, but being an identical twin is a bit cooler. It's really weird to think that I'm basically Caitlin!' The sisters remain close and continue to support each other through Caitlin's treatment.
