Mutations in SPAG1 Cause Primary Ciliary Dyskinesia Associated with Defective Outer and Inner Dynein Arms

Abstract

Primary ciliary dyskinesia (PCD) is a genetically heterogeneous, autosomal-recessive disorder, characterized by oto-sino-pulmonary disease and situs abnormalities. PCD-causing mutations have been identified in 20 genes, but collectively they account for only ∼65% of all PCDs. To identify mutations in additional genes that cause PCD, we performed exome sequencing on three unrelated probands with ciliary outer and inner dynein arm (ODA+IDA) defects. Mutations in SPAG1 were identified in one family with three affected siblings. Further screening of SPAG1 in 98 unrelated affected individuals (62 with ODA+IDA defects, 35 with ODA defects, 1 without available ciliary ultrastructure) revealed biallelic loss-of-function mutations in 11 additional individuals (including one sib-pair). All 14 affected individuals with SPAG1 mutations had a characteristic PCD phenotype, including 8 with situs abnormalities. Additionally, all individuals with mutations who had defined ciliary ultrastructure had ODA+IDA defects. SPAG1 was present in human airway epithelial cell lysates but was not present in isolated axonemes, and immunofluorescence staining showed an absence of ODA and IDA proteins in cilia from an affected individual, thus indicating that SPAG1 probably plays a role in the cytoplasmic assembly and/or trafficking of the axonemal dynein arms. Zebrafish morpholino studies of spag1 produced cilia-related phenotypes previously reported for PCD-causing mutations in genes encoding cytoplasmic proteins. Together, these results demonstrate that mutations in SPAG1 cause PCD with ciliary ODA+IDA defects and that exome sequencing is useful to identify genetic causes of heterogeneous recessive disorders.

Inherited biallelic CSF3R mutations in severe congenital neutropenia

“…Ciliary dyskinesia is associated with recurrent sinopulmonary infections. 26 It is therefore possible that P2 suffers additionally from a ciliary disorder, which may contribute to her recurrent infections.…”

Quantitative Proteomic Analysis of Human Airway Cilia Identifies Previously Uncharacterized Proteins of High Abundance

“…PCD is a genetically heterogeneous disease, with causative mutations in over 30 genes identified (7). Many of these mutations are in genes that encode structural proteins of the axoneme itself (e.g., DNAI1, DNAH5) (8, 9) but others encode cytoplasmic assembly or regulatory proteins (e.g., SPAG1, MCIDAS, HEATR2 (10–12). These mutations impair ciliary function and result in impaired or absent mucociliary clearance.…”

Ciliary beat pattern and frequency in genetic variants of primary ciliary dyskinesia

“…Mutations in nine genes affect outer dynein arm (ODA) components: DNAI1, DNAI2, DNAH5, DNAL1, CCDC103, NME8/TXNDC3, CCDC114 and ARMC4 [1,6,7] result in ODA defects, whereas DNAH11 mutations result in PCD with normal ultrastructure [8]. Nine genes encode the cytoplasmic proteins required for the assembly of both ODA and inner dynein arm (IDA) complexes: KTU/DNAAF1, LRRC50/DNAAF2, C19orf51/DNAAF3, LRRC6, HEATR2, DYX1C1/DNAAF4, ZMYND10, SPAG1 and C21orf59 [1,[9][10][11][12]. Mutations in CCDC39 and CCDC40 result in an IDA and microtubular disorganisation defect [13,14].…”