A pair of identical twin girls have been diagnosed with leukaemia, in a case that scientists believe adds to evidence that the disease develops in the womb.

Katie and Chelsea Young, who fell ill within weeks of each other, were diagnosed with childhood leukaemia after having routine tests for anaemia. The four-year-old girls, from Brecon, Powys, will receive treatment at a cancer unit near Cardiff next week.

Doctors believe the diagnosis adds weight to the theory that a genetic defect developed before birth and then triggered by an infection in early life lies at the root of the cancer.