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Burkard, Markus; Kohl, Susanne; Kratzig, Timm; Tanimoto, Naoyuki; Brennenstuhl, Christina; Bausch, Anne E.; Junger, Katrin; Reuter, Peggy; Sothilingam, Vithiyanjali; Beck, Susanne C.; Huber, Gesine; Ding, Xi-Qin; Mayer, Anja K.; Baumann, Britta; Weisschuh, Nicole; Zobor, Ditta; Hahn, Gesa-Astrid; Kellner, Ulrich; Venturelli, Sascha; Becirovic, Elvir; Charbel Issa, Peter; Koenekoop, Robert K.; Rudolph, Gunther; Heckenlively, John; Sieving, Paul; Weleber, Richard G.; Hamel, Christian; Zong, Xiangang; Biel, Martin; Lukowski, Robert; Seeliger, Matthias W.; Michalakis, Stylianos; Wissinger, Bernd; Ruth, Peter (2018): Accessory heterozygous mutations in cone photoreceptor CNGA3 exacerbate CNG channel-associated retinopathy. In: The Journal of Clinical Investigation, Vol. 128, No. 12: pp. 5663-5675
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Mutations in CNGA3 and CNGB3, the genes encoding the subunits of the tetrameric cone photoreceptor cyclic nucleotide-gated ion channel, cause achromatopsia, a congenital retinal disorder characterized by loss of cone function. However, a small number of patients carrying the CNGB3/c.1208G\textgreaterA;p.R403Q mutation present with a variable retinal phenotype ranging from complete and incomplete achromatopsia to moderate cone dysfunction or progressive cone dystrophy. By exploring a large patient cohort and published cases, we identified 16 unrelated individuals who were homozygous or (compound-)heterozygous for the CNGB3/c.1208G\textgreaterA;p.R403Q mutation. In-depth genetic and clinical analysis revealed a co-occurrence of a mutant CNGA3 allele in a high proportion of these patients (10 of 16), likely contributing to the disease phenotype. To verify these findings, we generated a Cngb3R403Q/R403Q mouse model, which was crossbred with Cnga3-deficient (Cnga3-/-) mice to obtain triallelic Cnga3+/- Cngb3R403Q/R403Q mutants. As in human subjects, there was a striking genotype-phenotype correlation, since the presence of 1 Cnga3-null allele exacerbated the cone dystrophy phenotype in Cngb3R403Q/R403Q mice. These findings strongly suggest a digenic and triallelic inheritance pattern in a subset of patients with achromatopsia/severe cone dystrophy linked to the CNGB3/p.R403Q mutation, with important implications for diagnosis, prognosis, and genetic counseling.