Purchase this article with an account.
P.A. Good, S. Banerjee, I. Aligianis, R. Siddiqi, S. Johnson, J.R. Ainsworth, M. Michaelides, D. Hunt, T. Moore; Electroretinography in the Definition of Phenotypes of Rod Monochromatism . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1488.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: Congenital Achromatopsia, (Rod Monochromatism) is an autosomal recessive stationary condition with an absence of functioning cones. Incomplete/progressive forms have been described with some preservation of colour vision and better visual acuity. The Electroretinogram is thought to be pathogmonic of rod monochromatism, but there are few studies comparing it with progressive forms of cone dystrophy. Three candidate genes; CNGA3, CNGB3 and GNAT2 have been associated with rod monochromatism, whilst mutations of CNGA3 are associated with progressive forms. This study investigates 9 Pakistani families with achromatopsia assessing the role of the ERG in identifying the phenotype in each family. Methods: Nine families (15 patients) of Pakistani origin underwent ISCEV standardised ERG, colour vision analysis (Farnsworth 100 hue), and gene-linkage studies. Five of the families were phenotypic of rod monochromatism, and 4 of progressive cone dystrophy. Results: In the families with complete achromatopsia all of the recorded ERGs revealed delayed scotopic responses at high intensity (+1 log unit ) stimulation, grossly reduced photopic responses, and absent cone (30Hz) responses. Children (3) in two of the families labelled as progressive cone dystrophy also revealed these ERG changes, and in one family one child had ERG changes phenotypic of rod monochromatism, but was symptomatically progressive, although her Mother and Uncle had ERG and colour vision changes of mild progressive cone dystrophy (progressive reductions of the 30 Hz (cone) ERG only). She was found to have mutations of both CNGA3 and GNAT2, whereas her Mother and Uncle had CNGA3 mutations only. In the other two families with presumed progressive cone dystrophy the Scotopic ERGs were normal, photopic ERGs were reduced, and cone ERGs were grossly reduced but present. These were found to have CNGA3 mutations. Conclusions: The ERG, plays an important role in defining the phenotypes of cone dystrophy, allowing differentiation between rod monochromatism characterised by delayed scotopic ERGs and absent 30Hz (cone) ERGs, and progressive cone dystrophy; characterised by normal scotopic ERGs and partially preserved cone ERGs. The families in this study may suggest that rod monochromatism and progressive cone dystrophy are part of a spectrum, their incidence dependant on the single or combined mutations of CNGA3,CNGB3, and GNAT2, and possibly other candidate genes yet to be identified.
This PDF is available to Subscribers Only