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Farid Afshar, Gavin Arno, Rola Ba-Abbad, Simona Degli Esposti, Michel Michaelides, Andrew Webster, Omar Mahroo; Awareness of olfactory impairment in a cohort of patients with CNGB1-associated retinitis pigmentosa. Invest. Ophthalmol. Vis. Sci. 2019;60(9):5423.
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© ARVO (1962-2015); The Authors (2016-present)
The CNGB1 gene encodes a protein involved in both photoreceptor and olfactory signal transduction. Patients with retinitis pigmentosa (RP) due to bi-allelic variants in this gene have previously been reported to describe no olfactory problems. However, a subsequent quantitative study found objectively reduced olfactory function in 8 of 9 patients tested, with 3 aware of their olfactory impairment. Variants can occur in the N-terminal glutamic acid-rich protein (GARP) or the channel domain. The GARP domain has an important role in rod photoreceptors, but its role in olfactory neurons is less clear. We investigated awareness of olfactory problems in our cohort of molecularly characterised patients, and identified in which domain variants occurred.
The electronic inherited retinal disease database of Moorfields Eye Hospital was searched for patients with a molecular diagnosis of CNGB1-associated RP. These patients were contacted and asked whether they were aware of any problems with their sense of smell. Disease-causing variants were also classified as to whether they occurred within the GARP or channel domain of the protein.
Nineteen affected patients (mean (SD) age 60 (11) years; 11 females) from 18 separate families were identified. Fifteen patients (79%) were successfully contacted. Of these, six patients (40%) reported a reduced or absent sense of smell; the remainder reported no problems. Eight out of the 15 patients contacted had at least one disease-causing variant in the GARP domain. Of these 8 patients, only one was aware of a reduced sense of smell. Of the remaining 7 patients, 5 reported a reduced or absent sense of smell. The difference in proportions was significant (p=0.04, Fisher exact test).
Our findings confirm that a substantial proportion of patients with CNGB1-associated retinopathy report a reduced or absent sense of smell when specifically questioned. In our cohort, patients with at least one variant in the GARP domain appeared to be less likely to be aware of olfactory impairment than those in whom one or both mutations were in the channel domain.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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