RSPH4A-PCDx: An Index to Predict Lung Function Decline in Primary Ciliary Dyskinesia.

Primary ciliary dyskinesia (PCD) is a rare, genetically heterogeneous disorder that impairs mucociliary clearance and leads to progressive lung disease. This study aimed to characterize lung function decline in a genetically homogeneous cohort of Puerto Rican patients with RSPH4A-associated PCD and to develop a clinical tool to predict lung function decline and support transplant referral decisions. We conducted a retrospective chart review of patients (n = 25) with a confirmed RSPH4A [c.921+3_6delAAGT] genetic variant, collecting longitudinal spirometry data and applying linear regressions to calculate each patient's individual FEV₁ decline. The median FEV₁ at diagnosis was 55%, with a median annual decline of -0.75% predicted. Adults exhibited significantly lower lung function compared to pediatric patients, while no difference was seen between males and females. Based on this observed decline, we developed the Predicted Capacity Decline Index (PCDx), an index that estimates the age and time until a patient reaches the 30% FEV₁ threshold, the point at which lung transplant referral is typically considered. Our findings underscore the need for early intervention and suggest that genotype-specific tools like the PCDx may enhance clinical decision-making in managing progressive lung disease in PCD.