The first dozen Parkinson's patients to have holes drilled in their skulls for a novel gene therapy attempt weren't harmed-and hints at some improvement have researchers embarking on a larger study to see if the treatment really may work. Doctors reported initial results of the closely watched experiment at a neurology meeting,but cautioned that it's far too soon to raise hopes. It helps using a nerve growth factor to try to rescue dying brain cells. Some 1.5 million Americans have Parkinson's,a disease that gradually destroys brain cells that produce dopamine,a chemical crucial for the cellular signaling that controls muscle movement.Too little dopamine causes increasingly severe tremors and periodically stiff or frozen limbs.