Meet Billy and Leo, brothers with the same rare genetic disease called spinal muscular atrophy or SMA. However, their journeys with SMA have been remarkably different. Billy was diagnosed with SMA at 15 months when he began to lose motor skills he had already mastered. Fortunately, a new gene therapy became available, and within a month after treatment, Billy was able to bear weight on his legs, lift his arms up, and achieve developmental milestones. Baby brother Leo was diagnosed in utero and received the same gene therapy at just 17 days old, before symptoms even appeared. Today, Billy, 8, has muscle weakness but walks independently with braces for support, plays with his friends, and participates in sports like baseball and karate. Leo, 3, is asymptomatic and does what you would expect an age-appropriate 3-year-old to do. He runs, jumps, climbs, and loves his truck and car toys. "They are brothers born only a few years apart, yet in some ways they represent two different chapter...