U. S. scientists have created the first human model to study a devastating nerve disease. This uses skin cells from a child with spinal muscular atrophy (SMA) and will allow the researchers to watch the disease develop and perhaps find a way to treat it.

SMA is a genetic disease that attacks motor neurons in the spinal cord and is caused by a deficiency of a protein called spinal muscular atrophy, without which motor neurons which are important for muscle function, die.

Scientists from the University of Wisconsin-Madison and the University of Missouri-Columbia grew batches of nerve cells with the same genetic defects by first turning the cells into stem cells from a powerful new type of cell called induced pluripotent stem cells, or iPS cells, which behave like embryonic stem cells and then induced these cells to become motor neurons.

A similar process was repeated on cells from the child's healthy mother. The motor neurons from the child's cells began to die after two months while the mother's neurons kept developing normally. Clive Svendsen of the University of Wisconsin-Madison said, "We suddenly had a split and it was related to the lack of the SMN protein." He added "That SMN protein is important for motor neuron survival. They are the cells that make muscles move."

Reported in the journal Nature, Svendsen said as iPS cells can grow for years in the lab and the experiment can be repeated in different batches of cells researchers can replay the process. "Now you can replay the human disease over and over in the dish and ask what are the very early steps that began the process."

Svendsen said the discovery would help drug makers test potential treatments to prevent nerve death in SMA. His lab is one of many using iPS cells as a new tool for studying disease.