None of the five individuals harboring biallelic DNAH9 mutant variants were clinically diagnosed with PCD (Table 1). However, mild respiratory symptoms including frequent cold-like infections were observed in individuals OP-2905 II1, MS-SI46 II1, and MD II.1. The nasal NO production rate was measured 76 nL/min for OP-2905 II1 (one occasion) and 106 nL/min (first occasion, 2011) and 67 nL/min (second occasion, 2015) for OP-1226 II1 using the EcoMedics CLD88 (EcoMedics) system. Thus, the nasal NO production rate was in the low range but above the cut-off value for PCD previously reported by most studies (30–52.5 nL/min)35, 36 and only minimally below the cut-off value reported in two other studies (77 nL/min and 82 nL/min)37, 38 used for PCD screening.