When the FDA convened an advisory committee in October 2012 to help it decide whether to approve the drug, one patient, a 20-year-old man named Christian Jacobs, described being so terrified by his disease that he often had written goodbye notes to his family before going to bed.

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Christian Billingsley, now 17, was 3 months old when he started projectile vomiting, the first evidence the disease was attacking every part of his body, especially his kidneys, which failed when he was 18 months old.

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