PDZD7 is a modifier of retinal disease and a contributor to digenic Usher syndrome
Inga Ebermann, … , Thomas Benzing, Hanno J. Bolz
Inga Ebermann, … , Thomas Benzing, Hanno J. Bolz
Published May 3, 2010
Citation Information: J Clin Invest. 2010;120(6):1812-1823. https://doi.org/10.1172/JCI39715.
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Research Article Ophthalmology

PDZD7 is a modifier of retinal disease and a contributor to digenic Usher syndrome

Abstract

Usher syndrome is a genetically heterogeneous recessive disease characterized by hearing loss and retinitis pigmentosa (RP). It frequently presents with unexplained, often intrafamilial, variability of the visual phenotype. Although 9 genes have been linked with Usher syndrome, many patients do not have mutations in any of these genes, suggesting that there are still unidentified genes involved in the syndrome. Here, we have determined that mutations in PDZ domain–containing 7 (PDZD7), which encodes a homolog of proteins mutated in Usher syndrome subtype 1C (USH1C) and USH2D, contribute to Usher syndrome. Mutations in PDZD7 were identified only in patients with mutations in other known Usher genes. In a set of sisters, each with a homozygous mutation in USH2A, a frame-shift mutation in PDZD7 was present in the sister with more severe RP and earlier disease onset. Further, heterozygous PDZD7 mutations were present in patients with truncating mutations in USH2A, G protein–coupled receptor 98 (GPR98; also known as USH2C), and an unidentified locus. We validated the human genotypes using zebrafish, and our findings were consistent with digenic inheritance of PDZD7 and GPR98, and with PDZD7 as a retinal disease modifier in patients with USH2A. Pdzd7 knockdown produced an Usher-like phenotype in zebrafish, exacerbated retinal cell death in combination with ush2a or gpr98, and reduced Gpr98 localization in the region of the photoreceptor connecting cilium. Our data challenge the view of Usher syndrome as a traditional Mendelian disorder and support the reclassification of Usher syndrome as an oligogenic disease.

Authors

Inga Ebermann, Jennifer B. Phillips, Max C. Liebau, Robert K. Koenekoop, Bernhard Schermer, Irma Lopez, Ellen Schäfer, Anne-Francoise Roux, Claudia Dafinger, Antje Bernd, Eberhart Zrenner, Mireille Claustres, Bernardo Blanco, Gudrun Nürnberg, Peter Nürnberg, Rebecca Ruland, Monte Westerfield, Thomas Benzing, Hanno J. Bolz

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Figure 5

Loss of Pdzd7a results in structural defects, retinal cell death, and protein mislocalization.

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Loss of Pdzd7a results in structural defects, retinal cell death, and pr...
(A–D) Phalloidin-stained hair bundles of the anterior crista in 5dpf control (A, B) and pdzd7aMO-injected (C, D) larvae. Stereocilia in controls are upright and tapered (asterisks), whereas bundles are bent and disorganized after morpholino injection. (E) Graph of average number of dying photoreceptor cells, assayed by anti-active caspase-3 labeling, in control and morpholino-injected fish. Morpholino combinations and dosages (either full: 1.0; or half: 0.5) are indicated for each group. n = 20 for each category. *P ≤ 10–6 derived from Student’s t test comparing retinal cell death rates in morphant larvae to those of control animals. SEM is indicated by error bars for each group. (F–I) High magnification scans of photoreceptor cells in 5dpf larvae showing localization of Pdzd7 (F, G) and Gpr98 (H, I) antibodies (red) in control and pdzd7aMO injected larvae; acetylated tubulin in green in all panels. In the control, Pdzd7a (red, F) and Gpr98 (red, H) are present at the base of the connecting cilia (small arrows). Images taken from a single focal plane. Gpr98 is also present at the photoreceptor synapse (large arrows), where Pdzd7a is not detected. Labeling by both antibodies is reduced at the connecting cilium after pdzd7aMO injection (G, I), whereas synaptic localization is unaffected by pdzd7 knockdown. Scale bars: 10 μm (A, C); 5 μm (B, D); 5 μm (F–I).