Clinical Utility of NGS-Based Diagnosis in Primary Ciliary Dyskinesia: Experience from a Brazilian Pediatric Cohort at a Reference Center for Rare Diseases

Background: Primary ciliary dyskinesia (PCD) is a rare and genetically heterogeneous disorder that remains underdiagnosed in low- and middle-income countries, largely due to limited access to specialized diagnostic tests. Genetic analysis has become an essential component of PCD diagnosis, particularly where functional and ultrastructural evaluations are unavailable. Methods: We conducted an investigational study including children and adolescents with clinical suspicion of PCD followed at a Brazilian tertiary center. Clinical characterization included detailed phenotyping and calculation of the PICADAR score. Molecular investigation was performed using exome sequencing as a frontline diagnostic approach. Results: Among 27 individuals evaluated, 10 (37%) received a confirmed molecular diagnosis of PCD. An additional 6 (22%) individuals had inconclusive molecular findings, mainly due to variants of uncertain significance (VUS), and were classified as likely PCD based on combined clinical and molecular evidence. Higher PICADAR scores were more frequently observed among individuals with confirmed or likely molecular diagnosis, with 9 of 10 confirmed cases presenting a score above 5. Beyond PCD-associated findings, exome sequencing also enabled the identification of clinically relevant additional diagnoses, including cystic fibrosis, FGFR3-related hypochondroplasia, and ACMG-reportable secondary finding involving BRCA2. Some unresolved cases may also reflect inherent technical limitations of exome sequencing, including restricted sensitivity for copy-number variants, suboptimal coverage of highly homologous or GC-rich regions, and limited detection of deep intronic and other variants. Additional factors include challenges in variant interpretation and incomplete knowledge of disease-associated genes. Conclusions: Frontline exome sequencing is a valuable diagnostic tool for PCD, particularly when integrated with robust clinical phenotyping. Clinical scoring systems such as PICADAR may help prioritize individuals for genetic testing and optimize diagnostic yield in resource-limited settings.