Delineation of CCDC39/CCDC40 mutation spectrum and associated phenotypes in primary ciliary dyskinesia

Background

CCDC39 and CCDC40 genes have recently been implicated in primary ciliary dyskinesia (PCD) with inner dynein arms (IDA) defects and axonemal disorganization; their contribution to the disease is, however, unknown. With the aim to delineate CCDC39/CCDC40 mutation spectrum and associated phenotypes, we screened a large cohort of patients with IDA defects, and accurately described their clinical and ciliary phenotypes.

Methods

All CCDC39 and CCDC40 exons and intronic boundaries were sequenced in 43 patients from 40 unrelated families. We recorded and compared clinical features (sex, origin, consanguinity, laterality defects, ages at first symptoms and evaluation, neonatal respiratory distress, airway infections, nasal polyposis, otitis media, bronchiectasis, infertility), ciliary beat frequency and quantitative ultrastructural analyses of cilia and sperm flagella.

Results

Biallelic CCDC39 or CCDC40 mutations were identified in 30/34 (88.2%) unrelated families with IDA defects and axonemal disorganization (22 and 8 families, respectively). Fourteen of the 28 identified mutations are novel. No mutation was found in the 6 families with isolated IDA defects. Patients with identified mutations shared a similar phenotype, in terms of both clinical features and ciliary structure and function. The sperm flagellar ultrastructure, analyzed in 4/7 infertile males, evidenced abnormalities similar to the ciliary ones.

Conclusions

CCDC39 and CCDC40 mutations represent the major cause of PCD with IDA defects and axonemal disorganization. Patients carrying CCDC39 or CCDC40 mutations are phenotypically indistinguishable. CCDC39 and CCDC40 analyses in selected patients ensure to find mutations with high probability, even if clinical or ciliary phenotypes cannot prioritize one analysis over the other.