Ciliary Dyskinesia, Primary, 25

A number sign (#) is used with this entry because primary ciliary dyskinesia-25 (CILD25) is caused by homozygous or compound heterozygous mutation in the DYX1C1 gene (DNAAF4; 608706) on chromosome 15q21.

Description

Primary ciliary dyskinesia-25 is an autosomal recessive disorder caused by defective ciliary movement. Affected individuals have recurrent upper and lower airway disease, bronchiectasis, and decreased fertility. About half of patients show laterality defects, including situs inversus totalis. Respiratory cilia from patients show defects in the inner and outer dynein arms (summary by Tarkar et al., 2013).

For a phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see 244400.

Clinical Features

Tarkar et al. (2013) reported 12 patients with classic primary ciliary dyskinesia. Symptoms included recurrent upper and lower airway disease and bronchiectasis. Seven patients had neonatal respiratory distress syndrome. Four patients had reduced fertility. Five (42%) of the 12 affected individuals had situs inversus totalis, 2 (16%) had situs ambiguous (16%), 1 with dextrocardia and polysplenia and 1 with left atrial isomerism and polysplenia, and 5 (42%) had situs solitus. None of the patients had dyslexia, but 2 had a learning disability, which could be attributed to other causes, including microcephaly. Respiratory cilia from patients showed severe ultrastructural defects in both the inner and outer dynein arms, and cilia were either immotile or showed a reduced beat frequency compared to controls.

Inheritance

The transmission pattern of CILD25 in the families reported by Tarkar et al. (2013) was consistent with autosomal recessive inheritance.

Molecular Genetics

In 12 patients with primary ciliary dyskinesia-25, Tarkar et al. (2013) identified 9 different mutations in the DYX1C1 gene (see, e.g., 608706.0003-608706.0006). All mutations occurred in homozygous or compound heterozygous state and segregated with the disorder in the families. Seven of the 9 mutations were predicted to result in a truncated protein that would lack more than half of the protein. Immunofluorescence studies showed absence of or reduction in levels of proteins normally present in inner and outer dynein arm complexes, suggesting abnormalities in cytoplasmic preassembly.

Animal Model

Tarkar et al. (2013) found that homozygous deletion of exons 2-4 of the Dyx1c1 gene in mice resulted in increased embryonic lethality and caused phenotypes consistent with motile cilia defects, including hydrocephalus and laterality defects. Cilia on ependymal cells derived from mutant mice showed a lack of ciliary beating and cilia on respiratory cells showed absence of the inner and outer dynein arm structures. This phenotype was independently confirmed in an ENU mutant mouse ('Sharpei') with a T2A start codon mutation in the Dyx1c1 gene: Sharpei mice had congenital heart defects and laterality defects, as well as immotile ependymal and tracheal cilia. In wildtype mouse embryos, Dyx1c1 was expressed in pit cells of the embryonic node. Knockdown of Dyx1c1 in zebrafish also resulted in phenotypes associated with ciliary defects, such as body curvature, hydrocephalus, cystic kidneys, and situs inversus.