Cilia Dynamics in Primary Ciliary Dyskinesia: A Biophysical Characterization of the RSPH4A Founder Variant

Primary ciliary dyskinesia (PCD) is a rare ciliopathy resulting in chronic oto-sino-pulmonary disease. PCD diagnosis can be achieved by a combination of different diagnostic and adjuvant tools, including high-speed video-microscopy analysis (HSVA). A founder variant has been described in Puerto Rico as the most common cause of PCD in the island. Background/Objectives: In HSVA, objective parameters such as ciliary beat frequency (CBF) and subjective parameters such as ciliary beat pattern (CBP) shed light on the biophysical properties of cilia. However, the subjective nature of CBP creates a gap in knowledge; characteristics such as the length, angle, and bending index of cilia are poorly described. Our goal is to quantify cilia dynamics of the RSPH4A (c. 921+3₉21+6delAAGT (intronic) ) founder variant in Puerto Rico through biophysical properties of cilia. This approach enhances longitudinal patient care by understanding treatment progress through biophysical ciliary function. Methods: We analyzed images from HSVA of six patients with PCD homozygous for the founder variant and six healthy controls (HC) (n = 12). Results: We found that ciliary length (PCD = 7. 62 ± 0. 95 μm, HC = 8. 12 ± 1. 36 μm, p = 0. 204 ns), orientation vector (PCD = 7. 20 ± 0. 93 μm, HC = 7. 25 ± 1. 01 μm, p = 0. 883 ns), straight angle (PCD = 1. 67 ± 0. 27 rad, HC = 1. 76 ± 0. 29 rad, p = 0. 380 ns), and area (PCD = 2. 35 ± 0. 52 μm2, HC = 2. 10 ± 0. 53 μm2, p = 0. 264 ns) did not have statistically significant differences between PCD and HC. In contrast, bending index (PCD = 1. 06 ± 0. 04, HC = 1. 12 ± 0. 09, p = 0. 01), bent angle (PCD = 1. 11 ± 0. 30 rad, HC = 0. 67 ± 0. 21 rad, p < 0. 0001), net angle (PCD = 0. 56 ± 0. 26 rad, HC = 1. 09 ± 0. 35 rad, p < 0. 0001), amplitude (PCD = 5. 77 ± 1. 25 μm, HC = 7. 99 ± 1. 65 μm, p < 0. 0001), and amplitude per second (PCD = 48. 83 ± 13. 23 A (s), HC = 91. 66 ± 27. 96 A (s), p < 0. 0001) showed significant differences between both groups. Conclusions: Reduced angular excursion and amplitude in PCD demonstrate that the beating pattern of the RSPH4A founder variant is dysfunctional as compared with healthy controls. Our study provides an objective framework to understand the biophysical properties of the RSPH4A founder variant.