Primary ciliary dyskinesia (PCD) is a rare inherited condition that makes it hard for the body to clear germs from the lungs and nose, causing frequent infections. It is often confused with other illnesses, so genetic testing is important for a correct diagnosis. One tricky gene involved is HYDIN, as it has a nearly identical copy called HYDIN2. By showing that HYDIN2 is not active in airway cells, we used RNA from nasal tissue samples to pinpoint genetic changes in HYDIN. Our approach improves PCD diagnosis and could help identify other genetic diseases with similar challenges. (by Minako Hijikata, Kozo Morimoto, Masashi Ito, Keiko Wakabayashi, Akiko Miyabayashi, and Naoto Keicho, https://jmg.bmj.com/content/early/2025/01/12/jmg-2024-110400 )