B47-31 HYDIN in Plain Sight

Abstract Introduction Primary ciliary dyskinesia (PCD) is a rare genetic condition characterized by dysfunctional motile cilia leading to abnormal mucociliary clearance. PCD is a heterogenous disease with over 50 disease causing mutations having been described. Pathogenic mutations in the HYDIN gene have been recognized to cause PCD. We identified two cases with confirmed HYDIN-related PCD who attend the respiratory clinic in Galway University Hospital and sought to compare them. Case Reports Case 1 A 38-year-old male, never smoker, presented to clinic at 29 years of age with a 5-year history of productive cough, and frequent exacerbations of asthma. Past medical history was significant for chronic nasal congestion, asthma diagnosed at 7 years of age, and a hospital admission at 9 months of age for “grunting”. CT thorax showed bronchiectasis in the left lower lobe and lingula. Pulmonary function tests (PFTs) showed a preserved FEV1 of 4.49L (104%). 3 years later, he reported fertility issues and ongoing recurrent respiratory tract infections. CF genotyping was negative, and bronchoscopy showed mucopurulent secretions and cultured Haemophilus influenzae. Progression in symptoms prompted nasal nitric oxide (nNO) measurement and subsequent genetic analysis which revealed a pathogenic bi-allelic HYDIN mutation, confirming PCD. Case 2 A 64-year-old female presented to clinic with recurrent sinusitis and chronic productive cough. Her past medical history includes bronchiectasis with left lower lobectomy at 12 years of age, hearing loss, multiple sinus surgeries, recurrent RTI and otitis media, as well as previous fertility issues necessitating in vitro fertilisation. Spirometry showed an obstructive pattern with FEV1 1.93L (75%), and FEV1/FVC 64%. CT thorax showed bronchiectasis in the medial aspect of the right middle lobe and both lower lobes. Years later, she reported worsening shortness of breath on exertion and increased frequency of RTI. Genetic analysis revealed a pathogenic bi-allelic mutation in HYDIN, confirming PCD. Discussion HYDIN-related PCD typically presents with a sinopulmonary phenotype but lacks laterality defects. Lung function may be preserved well into adulthood and radiographic bronchiectasis may be mild, which often leads to delayed diagnosis. Complex genetics and ultrastructural analyses further impact diagnosis. These two cases highlight the importance of recognising that PCD is a genetically and clinically heterogenous condition. Early diagnosis can have important implications for our patients. This abstract is funded by: None