After all, tests in many laboratories showed that providing normal copies of the gene should enable patients to make healthy copies of the protein specified by the gene. (scientificamerican.com)
As they age, they are at higher risk of developing mutations in the remaining normal copy of the gene. (source.wustl.edu)
But oddly enough, the team found that a large percentage of the resulting mice in their study that inherited only normal copies of the gene from their heterozygous parents did in fact have the white spots. (scientificamerican.com)