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M. H. Wiesen, L. T. Sharpe, E. Zrenner, S. Kohl, B. Wissinger, H. Jägle; Rod Function in Patients With CNGA3 and CNGB3 Mutations. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1267. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Mutations in the CNGA3 and CNGB3 gene encoding the alpha- and beta-subunit of the cyclic nucleotide-gated channel of the cone photoreceptors are the major cause of autosomal recessive complete achromatopsia. While most patients do not experience problems with rod function, standard ISCEV-ERG response amplitudes have been found to be slightly reduced in many patients. The aim of our study therefore was to describe rod function in patients with complete and incomplete achromatopsia resulting from CNGA3 or CNGB3 mutations.
43 patients aged 12 to 77 years underwent a standardized ophthalmic exam and electrophysiological visual function testing. Rod function was characterized by means of scotopic full-field ERG carried out according to ISCEV standards and the Naka-Rushton function with the parameters: (1) maximum b-wave amplitude (Vmax), (2) slope (n) at the linear phase, and (3) semisaturation intensity (k). Additionally, cone function was assesed by Lanthony D-15 saturated panel and/or anomaloscope. Ten healthy subjects served as controls. For all patients, molecular genetic analysis was performed by PCR amplification from total genomic DNA and subsequent direct DNA sequencing.
In this patient collection, 22 patients exhibited mutations in the CNGA3 and 19 patients in CNGB3 gene, while two patients carried mutations in both genes. Six patients showed incomplete achromatopsia with residual acuities between 0.1 and 0.6. For all other patients visual acuity was 0.2 or below. ISCEV rod threshold amplitude and implicit time was similar for all groups. Maximum response amplitude and Vmax was slightly lower for the CNGB3 group and both significantly (on average ca. 30%) below normals (p < 0.05). In contrast, the slope n was lower (on average ca. 40%) for normals and the semisaturation intensity k found to be similar for all groups. However, these differences were not significant.
Our data indicate that rod function in patients with CNGA3 and CNGB3 mutations is normal. Dark adapted ERG response amplitudes may be reduced for higher flash intensities consistent with significant cone contribution to these responses.
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