Ciliary dysfunction leads to a broad range of overlapping phenotypes, collectively termed ciliopathies. This grouping is underscored by genetic overlap, where causal genes can also contribute modifier alleles to clinically distinct disorders. Here we show that mutations in TTC21B, which encodes the retrograde intraflagellar transport protein IFT139, cause both isolated nephronophthisis and syndromic Jeune asphyxiating thoracic dystrophy. Moreover, although resequencing of TTC21B in a large, clinically diverse ciliopathy cohort and matched controls showed a similar frequency of rare changes, in vivo and in vitro evaluations showed a significant enrichment of pathogenic alleles in cases (P < 0.003), suggesting that TTC21B contributes pathogenic alleles to ∼5% of ciliopathy cases. Our data illustrate how genetic lesions can be both causally associated with diverse ciliopathies and interact in trans with other disease-causing genes and highlight how saturated resequencing followed by functional analysis of all variants informs the genetic architecture of inherited disorders.
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We are grateful to the individuals affected with ciliopathies and their families for their continued participation and enthusiasm. We thank N. Elkhartoufi for technical assistance, P. Parvex for subject recruitment, D. Parker for critical reading of the manuscript and Yorkshire Regional Genetics Service for help in obtaining control DNA samples. This research was supported by funds from the US National Institutes of Health grant R01HD04260 from the National Institute of Child Health and Development (N.K.), R01DK072301, R01DK075972 (N.K.), R01DK068306, R01DK064614, R01DK069274 (F.H.) and National Research Service Award (NRSA) fellowship F32 DK079541 (E.E.D.) from the National Institute of Diabetes, Digestive and Kidney disorders, RO1EY12910 from the National Eye Institute (E.A.P.), the Macular Vision Research Foundation (N.K.) the Foundation Fighting Blindness (N.K., R.A.L., E.A.P. and Q.L.), the F.M. Kirby Foundation (E.A.P.), the Rosanne Silbermann Foundation (E.A.P.), the Polycystic Kidney Disease (PKD) Foundation (C.B.), German Kidney Foundation (C.B.), German Research Foundation (DFG BE 3910/5-1 and SFB/TRR57; C.B.), UNADEV, Retina France, Programme Hospitalier de Recherche Clinique 2007, L'Agence nationale de la recherche 2009 (H.D.), a Medical Research Council (MRC) research training fellowship (J.H.) and the European Union (EU-SYSCILIA; E.E.D., C.A.J., P.L.B. and N.K.). This work was also supported in part by the Intramural Research Program of the National Human Genome Research Institute. R.A.L. is a Senior Scientific Investigator of Research to Prevent Blindness, New York, New York. P.L.B. is a Wellcome Trust Senior Research Fellow. F.H. is an Investigator of the Howard Hughes Medical Institute, a Doris Duke Distinguished Clinical Scientist and the Frederick G. L. Huetwell Professor. N.K. is a Distinguished George W. Brumley Professor.
The authors declare no competing financial interests.
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