Topological data analysis reveals genotype-phenotype relationships in primary ciliary dyskinesia

Primary ciliary dyskinesia (PCD) is a heterogeneous inherited disorder caused by mutations in approximately 50 cilia-related genes. PCD genotype-phenotype relationships have mostly arisen from small case series because existing statistical approaches to investigate relationships have been unsuitable for rare diseases. We applied a topological data analysis (TDA) approach to investigate genotype-phenotype relationships in PCD. Data from separate training and validation cohorts included 396 genetically defined individuals carrying pathogenic variants in PCD genes. To develop the TDA models, twelve clinical and diagnostic variables were included. TDA-driven hypotheses were subsequently tested using traditional statistics. Disease severity at diagnosis measured by FEV z-score was (i) significantly worse in individuals with mutations compared to other gene mutations and (ii) better in those with mutations; the latter also reported less neonatal respiratory distress. Patients without neonatal respiratory distress had better preserved FEV at diagnosis. Individuals with mutations were phenotypically diverse. Cilia ultrastructure and beat pattern defects correlated closely to specific causative gene groups, confirming these tests can be used to support a genetic diagnosis. This large scale multi-national study presents PCD as a syndrome with overlapping symptoms and variation in phenotype, according to genotype. TDA modelling confirmed genotype-phenotype relationships reported by smaller studies ( FEV worse with mutations), and identified new relationships, including FEV preservation with mutations and diversity of severity with mutations.