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.
Bibliographical noteFunding Information:
Funding support for research was provided to M.R.K., M.W.L., J.L.C., M.J.H., S.D. Dell, S.D. Davis, T.W.F., S.D.S., K.N.O., and M.A.Z. by US NIH/ORDR/NHLBI grant 5U54HL096458-06; to M.R.K., L.E.O., and M.A.Z. by NIH-NHLBI grant 5R01HL071798; to J.S. and D.A.N. by NIH-NHLBI grant 5R01HL094976; to M.J.B. by NIH-NHLBI grant RC2 HL-102923; and to J.S. by NIH-NHGRI grant 5R21HG004749. K.N.O. is supported by the Intramural Research Program of NIH-NIAID. Resequencing was provided through RS&G by NIH-NHLBI contract # HHSN268201100037C. The work was supported by NIH-NCATS grants UL1 TR000083 to UNC-CH and UL1 TR000154 to Colorado CTSI and CF foundation grant CFF R026-CR07. H. Omran is supported by funding from DFG Om6/4, IZKF Muenster Om2/009/12, and BESTCILIA and SYSCILIA from the European Community. F.H. is an investigator of the Howard Hughes Medical Institute.
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