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 grwoth 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.