Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: (CNN) Alex Gentile has a very simple wish. The 8-year-old wants to run with his friends on the playground. But because of a rare disease, he can't play in the sunlight for very long. Alex has X-linked reticulate pigmentary disorder with systematic manifestations -- or what's more commonly called XLPDR. It's so rare that there are only 18 diagnosed cases worldwide. Alex's story is part of photographer Luca Catalano Gonzaga's project, "Hopeful, 'One of a Kind,' " that documents invisible diseases. While many parents pride themselves on being vigilant, it's imperative for Alex's mother, Patrizia, to constantly monitor him. "When he overheats, he risks his life," she said. "A moment of negligence, a delay, and Alex dies."Alex Gentile is one of 18 people on Earth who've been diagnosed with XLPDRThe disorder makes the 8-year-old incredibly sensitive to sunlight 
 Question:Many times, patients with XLPDR are misdiagnosed, like _ was; identifying the gene will help doctors properly diagnose XLPDR patients in the future.

Alex Gentile