News of more incremental progress towards a cell transplant therapy to treat Parkinson's: "Parkinson's disease takes hold as cells that produce dopamine die off in part of the brain called the substantia nigra. This causes tremors, rigidity and slowness of movement, though patients may also experience tiredness, pain, depression and constipation, which worsen as the disease progresses. ... Brain cells that die off in Parkinson's disease have been grown from stem cells and grafted into monkeys' brains in a major step towards new treatments for the condition. US researchers say they have overcome previous difficulties in coaxing human embryonic stem cells to become the neurons killed by the disease. Tests showed the cells survive and function normally in animals and reverse movement problems caused by Parkinson's in monkeys. The breakthrough raises the prospect of transplanting freshly grown dopamine-producing cells into human patients to treat the disease. ... Previously we did not fully understand the particular signals needed to tell stem cells how to differentiate into the right type of cells. The cells we produced in the past would produce some dopamine but in fact were not quite the right type of cell, so there were limited improvements in the animals. Now we know how to do it right, which is promising for future clinical use."