A powerful new genetic sequencing technology has allowed scientists to sequence five-year-old Nicholas Volker's DNA, pinpoint the mutation causing his illness and arrive at an answer to the mystery. Sequencing revealed a more complex picture than the doctors at the Medical College of Wisconsin and Children's Hospital had suspected. The slightest mutation in a single gene has left Nicholas with not one, but two extremely rare, life-threatening illnesses. One of them, called XLP, is an inherited immune system disorder that affects fewer than one in a million children. His second disease, the gut illness marked by holes that pierce the intestine and skin, has never been identified until now. Nicholas is the first known case in medical history.