Scientists said they were astonished to discover that they could convert a person’s skin tissue into functioning nerve cells – bypassing an intermediate stem-cell stage – by the relatively simple procedure of adding a few short strands of RNA, a genetic molecule similar to DNA.

The breakthrough could soon lead to the generation of different types of human brain cells in a test tube which could be used to study a range of neurodegenerative conditions such as Parkinson’s and Alzheimer’s disease.

“A major problem in neurobiology has been the lack of a good human model. Neurons aren’t like blood. They’re not something people want to give up,” said Gerald Crabtree, professor of pathology at Stanford University Medical Centre in California.

The findings may also one day allow doctors to grow nerve cells directly from a patient’s skin cells to regenerate damaged parts of their brain or spinal cord.