In early November 2009, the Anderson family lost their 3-year-old son Henry to a mysterious illness. On Halloween night he was happy and healthy and trick or treating. And just two nights later, he was gone.

Over the next month, Darrin Anderson became consumed with finding out what had happened to Henry. Somewhere buried within his spreadsheet of more than 2,000 rare diseases lay the answer to Henry’s death. And though he didn’t know it at the time, it also contained the clue that would save the life of their younger son, Jack.

Read more in this article from the Milwaukee Journal Sentinel.