Olfactory dysfunction in patients with CNGB1-related retinitis pigmentosa

Abstract

Purpose : To report olfactory function and retinal phenotype in patients with bi-allelic mutations in CNGB1, a gene coding for a signal transduction channel subunit expressed in rod photoreceptors and olfactory sensory neurons.

Methods : In a multicenter study involving four tertiary referral centers, nine patients with CNGB1-related retinitis pigmentosa were recruited to investigate olfactory function using the standardized Sniffin Sticks test battery consisting of tests for odor threshold, odor discrimination and odor identification. In one patient, the T&T olfactometer was used. The ocular phenotype was also investigated using multimodal imaging and electroretinography.

Results : All patients had an early onset of night blindness, but were usually not diagnosed before the fourth decade due to a relatively slow retinal degeneration. Retinal features were characteristic for a rod-cone dystrophy. Olfactory testing revealed decreased or absent olfactory function, with all except one patient scoring in the lowest quartile in relation to age-related norms. Magnetic resonance brain imaging and electroencephalography measurements in response to olfactory stimulation were available for one patient and revealed diminished olfactory bulbs and reduced responses to odor, respectively. Molecular genetic testing identified four previously reported and six novel (c.1312C>T, c.2210G>A, c.2492+1G>A, c.2542_2543insA, c.2763C>G, c.3044_3050delGGAAATC) mutations in CNGB1.

Conclusions : Mutations in CNGB1 may cause an autosomal recessive retinitis pigmentosa-olfactory dysfunction syndrome, characterized by a relatively slow progression of retinal degeneration and variable hyposmia/anosmia.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.