Here is an example of the other use for stem cells: to grow tissue that can be used to test and understand specific diseases. "Researchers are applying new stem cell technology to use skin samples to grow the brain cells thought to be responsible for the onset of Parkinson's disease ... [the] team will be gathering data from over 1,000 patients with early stage Parkinson's disease and taking small samples of skin tissue to grow special stem cells - induced pluripotent stem cells (iPS cells). iPS cells can be generated from accessible tissue such as the skin and then used to generate specific types of cell. The researchers will use the iPS cells to grow dopamine neurons - the brain cells responsible for the production of dopamine, as it is these cells which die in patients with Parkinson's, leading to the onset of the disease. ... iPS cells provide new and exciting opportunities to grow and study dopamine neurons from patients for the first time. This technology will prove to be extremely important in diseases which affect the brain because of its relative inaccessibility - it's far easier to get a skin sample than a brain biopsy. Once we have neurons from patients we can compare the functioning of cells taken from patients with the disease and those without to better understand why dopamine neurons die in patients with Parkinson's."