Today there are more than 10,000 known rare diseases, defined by the European Union as conditions that affect less than 1 in 2,000 people and by the United States as those that affect fewer than 200,000 people. The vast majority of rare diseases are caused by or associated with detrimental mutations in protein-coding genes, making them prime candidates for correction with novel gene therapies and other gene-based medicines. Thanks to scientific advances in genetic engineering technologies over the last 20 years, clinical trials testing gene therapies and other gene-based medicines are more common than ever, with nearly 200 opening to enrollment in the United States this year alone