Clinical, Genetic, Morphological and Functional Correlations in a Large Series of Patients with Primary Ciliary Dyskinesia: A Heterogeneous Disease with a Controversial Diagnosis.

Abstract

Background and objective: Primary ciliary dyskinesia (PCD) is a rare genetic condition characterised by abnormal ciliary motility, primarily affecting the respiratory tract. Despite its clinical significance, there is currently no gold standard for PCD diagnosis. This study aims to address this diagnostic challenge by evaluating a comprehensive approach in a large cohort of patients with suspected PCD.

Methods: We conducted a retrospective analysis of 128 patients with suspected PCD at a specialised clinical reference unit. A thorough anamnesis was performed, followed by a triad of diagnostic tests: (i) a high-speed video analysis of ciliary beat pattern; (ii) transmission electron microscopy for ciliary ultrastructure examination; and (iii) a genetic analysis, primarily through clinical exome sequencing. Correlations between the clinical, morphological and genetic findings were studied. Functional assays on RNA were performed to assess new splicing variants. Pearson's chi-square test was used to compare categorical variables and comparisons of means were performed using the Student's t-test.

Results: A definitive PCD diagnosis was established in 72% of the studied patients. Notably, only 58% of the diagnosed cases showed positive results across all three diagnostic tests. Patients with immotile cilia have a higher frequency of neonatal respiratory distress and had a higher likelihood of receiving a genetic diagnosis. A high-speed video analysis was altered in 116 patients, 53 of them with immotile cilia. A transmission electron microscopy revealed ultrastructural alterations in 67 patients, with class 1 defects being more common. DNAH5, RSPH1 and DNAH11 were the most represented genes among the 18 causal genes found. Among the 71 causal genetic variants found, we highlight the overrepresentation of the c.85G>T in RSPH1 and describe the aberrant effect on RNA of the splicing variants DNAH11:c.11497-6T>G, DNAH9:c.2596-2dup, CCDC40:c.2597A>G and CCDC40:c.2832G>A. Finally, we describe a severe phenotype associated with the RSPH1 gene, contrary to previously reported data.

Conclusions: This comprehensive analysis of a large cohort of patients with PCD underscores the challenges in achieving a definitive diagnosis and emphasises the need for a multi-faceted diagnostic approach. This study enhances our understanding of this rare condition, including the identification of new splicing variants and an unexpected severe phenotype associated with RSPH1, challenging previous assumptions about genotype-phenotype correlations in PCD.