The human dynein intermediate chain 2 gene (DNAI2): cloning, mapping, expression pattern, and evaluation as a candidate for primary ciliary dyskinesia

Primary ciliary dyskinesia (PCD) is an autosomal recessive disease characterized by chronic sinusitis and bronchiectasis, and usually associated with hypofertility. Half of the patients present a situs inversus, defining the Kartagener's syndrome. This phenotype results from axonemal abnormalities of respiratory cilia and sperm flagella, i.e., mainly an absence of dynein arms. Recently, a candidate-gene approach, based on documented abnormalities of immotile strains of Chlamydomonas reinhardtii, allowed us to identify the first gene involved in PCD. Following the same strategy, we have characterized DNAI2, a human gene related to Chlamzydomonas IC69, and evaluated its possible involvement in a PCD population characterized by an absence of outer dynein arms. DNAI2, which is composed of 14 exons located at 17q25, is highly expressed in trachea and testis. No mutation was found in the DNAI2 coding sequence of the twelve patients investigated. However, ten intragenic polymorphic sites and an EcoRI RFLP have been identified, allowing the exclusion of DNAI2 in three consanguineous families.

Loss-of-function mutations in a human gene related to Chlamydomonas reinhardtii dynein IC78 result in primary ciliary dyskinesia

Primary ciliary dyskinesia (PCD) is a group of heterogeneous disorders of unknown origin, usually inherited as an autosomal recessive trait. Its phenotype is characterized by axonemal abnormalities of respiratory cilia and sperm tails leading to bronchiectasis and sinusitis, which are sometimes associated with situs inversus (Kartagener syndrome) and male sterility. The main ciliary defect in PCD is an absence of dynein arms. We have isolated the first gene involved in PCD, using a candidate-gene approach developed on the basis of documented abnormalities of immotile strains of Chlamydomonas reinhardtii, which carry axonemal ultrastructural defects reminiscent of PCD. Taking advantage of the evolutionary conservation of genes encoding axonemal proteins, we have isolated a human sequence (DNAI1) related to IC78, a C. reinhardtii gene encoding a dynein intermediate chain in which mutations are associated with the absence of outer dynein arms. DNAI1 is highly expressed in trachea and testis and is composed of 20 exons located at 9p13-p21. Two loss-of-function mutations of DNAI1 have been identified in a patient with PCD characterized by immotile respiratory cilia lacking outer dynein arms. In addition, we excluded linkage between this gene and similar PCD phenotypes in five other affected families, providing a clear demonstration of locus heterogeneity. These data reveal the critical role of DNAI1 in the development of human axonemal structures and open up new means for identification of additional genes involved in related developmental defects.