Doctors have used a new type of medicine called “gene silencing” to reverse a disease that leaves people in crippling pain.

The condition, acute intermittent porphyria, also causes paralysis and is fatal in some cases.

The novel approach fine-tunes the genetic instructions locked in our DNA.

Doctors say they are “genuinely surprised” how successful it is and that the same approach could be used in previously untreatable diseases.

Sue Burrell, from Norfolk, has endured pain few could imagine and needed to take strong opioid painkillers every day.

At one point her porphyria was causing severe attacks every couple of weeks and needed hospital treatment.

But even then morphine did not stop the pain.

She told the BBC it was worse than child-birth, saying: “It’s so intense – so strong it’s in your legs, in your back, and it just resonates everywhere. It’s really, really unbearable.”

Her sister was affected even more severely and was completely paralysed in hospital for two years.