RATIONALE: Primary Ciliary Dyskinesia (PCD), a genetic disorder of motile cilia, is associated with a range of clinical features including neonatal respiratory distress, chronic sino-oto-pulmonary disease, and laterality defects, including situs inversus totalis (approximately 50%) and heterotaxy (at least 6%). Heterotaxy is a disorder of ambiguous organ laterality frequently associated with congenital heart disease. Clinical symptoms in PCD can overlap with symptoms from congenital heart disease with heterotaxy. Nasal nitric oxide (nNO) levels are very low in PCD, but have not been studied systematically in heterotaxy. PCD-specific symptom criteria and nNO cut-off levels would help guide appropriate PCD screening within heterotaxy populations. METHODS: Two heterotaxy populations (age ≥5 years) were recruited. First, our multi-center consortium assessed individuals referred for suspected PCD due to sino-oto-pulmonary symptoms, including participants with heterotaxy. Second, one site (UNC) evaluated heterotaxy individuals followed in a cardiology clinic and never referred for suspected PCD. Both populations were investigated with symptom questionnaires and nNO measurements during palate closure. Those referred for suspected PCD also had electron microscopy (EM) of nasal cilia and genetic testing for PCD mutations. “Classic PCD” was diagnosed in participants with classic EM cilia defects and/or 2 PCD causing genetic mutations. Otherwise, participants were classified as “not classic PCD” and stratified by nNO level – those with nNO 100nL/min. RESULTS: Of 336 individuals referred for PCD symptoms, 30 (8.9%) have heterotaxy, including 15 with congenital heart disease. 15/30 have “classic PCD” and all of these have nNO 100nL/min (median 280; 137-338nL/min). The 12 cardiology clinic patients all have nNO >100nL/min (median 199; 127-287nL/min). Clinical features more prevalent in heterotaxy with “classic PCD” versus heterotaxy with nNO >100nl/min are: year-round wet cough (100% versus 26%, p<0.0001), year-round nasal congestion (93% versus 42%, p=0.001), bronchitis/pneumonia (93% versus 47%, p=0.003), recurrent otitis media (87% versus 53%, p=0.02), and chronic sinusitis (73% vs 37%, p=0.03). No significant differences were noted for clinical features in heterotaxy with “classic PCD” versus with low nNO levels. CONCLUSION: In heterotaxy, PCD-specific clinical features include year-round wet cough, year-round nasal congestion, bronchitis/pneumonia, otitis media, and sinusitis. nNO seems a sensitive screening test for PCD within heterotaxy. Presence of PCD specific clinical features and/or low nNO should prompt further PCD evaluation.