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Primary ciliary dyskinesia (PCD) is a genetically heterogeneous disease of motile cilia. Even though PCD is widely studied, North-African patients have been rarely explored. In this study, we aim at confirming the clinical diagnosis and explore the genetic spectrum of PCD in a cohort of Tunisian patients. Forty clinically diagnosed patients with PCD belonging to 34 families were recruited from Tunisian pediatric departments. In each proband, targeted capture PCD panel sequencing of the 40 PCD genes was performed. PCD panel sequencing identified bi-allelic mutations in 82% of the families in eight PCD genes. Remarkably, 23.5% of patients carried the same c.2190del CCDC39 mutation. Single nucleotide polymorphism profiling in six unrelated patients carrying this mutation has revealed a founder effect in North-African patients. This mutation is estimated to date back at least 1,400-1,750 years ago. The identification of this major allele allowed us to suggest a cost-effective genetic diagnostic strategy in North-African patients with PCD., (© 2019 Wiley Periodicals, Inc.)

Primary ciliary dyskinesia (PCD) is an autosomal recessive disease characterized by chronic respiratory infections of the upper and lower airways, hypofertility, and, in approximately half of the cases, situs inversus. This complex phenotype results from defects in motile cilia and sperm flagella. Among the numerous genes involved in PCD, very few-including CCDC39 and CCDC40-carry mutations that lead to a disorganization of ciliary axonemes with microtubule misalignment. Focusing on this particular phenotype, we identified bi-allelic loss-of-function mutations in GAS8, a gene that encodes a subunit of the nexin-dynein regulatory complex (N-DRC) orthologous to DRC4 of the flagellated alga Chlamydomonas reinhardtii. Unlike the majority of PCD patients, individuals with GAS8 mutations have motile cilia, which, as documented by high-speed videomicroscopy, display a subtle beating pattern defect characterized by slightly reduced bending amplitude. Immunofluorescence studies performed on patients' respiratory cilia revealed that GAS8 is not required for the proper expression of CCDC39 and CCDC40. Rather, mutations in GAS8 affect the subcellular localization of another N-DRC subunit called DRC3. Overall, this study, which identifies GAS8 as a PCD gene, unveils the key importance of the corresponding protein in N-DRC integrity and in the proper alignment of axonemal microtubules in humans., (© 2016 WILEY PERIODICALS, INC.)