Proceedings of The Physiological Society

Physiology 2014 (London, UK) (2014) Proc Physiol Soc 31, PCB075

Poster Communications

Genetic and environmental contributions to variation in human retinal responses: A twin study

T. Bhatti1,3, A. Tariq1,3, K. M. Williams1,3, C. J. Hammond1,3, O. Mahroo1,2

1. Ophthalmology, King's College London, London, United Kingdom. 2. Physiology, Development and Neuroscience, University of Cambridge, Cambridge, United Kingdom. 3. Twin Research and Genetic Epidemiology, King's College London, London, United Kingdom.

The relative contributions of genetic and environmental factors to the responses of the cell populations of the human retina are not known. The electroretinogram (ERG) represents the summed electrical response of the retina to light stimuli, and can be recorded non-invasively in vivo from human subjects. In this study we aimed to compare correlations within monozygotic (MZ) and dizygotic (DZ) twin pairs for both rod-driven and cone-driven ERGs to investigate genetic contributions to the variation in different response parameters.Twins were recruited from the TwinsUK cohort based at St Thomas' Hospital, London. Scotopic and photopic ERGs were recorded using conductive fibre electrodes (placed in the lower conjunctival fornix) from 172 twins (45 MZ and 41 DZ pairs), following pharmacological mydriasis, according to the protocol standardised by the International Society for Clinical Electrophysiology of Vision (ISCEV). Responses were recorded from both eyes, but responses from the right eye were used in the analysis; responses with very low signal-to-noise ratios were excluded. Twelve parameters were recorded for each subject: amplitudes and implicit times for scotopic "dim-flash" (0.01 cd m-2 s) b-wave (which is derived from rod bipolar cells) and "mixed-flash" (3 cd m-2 s) a-wave and b-wave (which derive from both rod and cone-driven systems), and for photopic 30 Hz flicker responses and photopic flash (3 cd m-2 s) a-wave and b-wave (photopic responses come exclusively from the cone system). Scotopic stimuli were delivered in the dark following at least 20 min of dark adaptation; photopic stimuli were delivered after on a white background (30 photopic cd m-2) following at least 10 min exposure to this background. Mean (SD) age was 62 (11) years. 93% of the twins were female. Correlations for most parameters were higher within MZ than DZ twin pairs. Correlations were very low for dim-flash b-wave implicit times (which might suggest a degree of imprecision in this measurement). For all other parameters, Pearson correlation coefficients for intra-pair correlation ranged from 0.50 to 0.87 for MZ twins, and from 0.28 to 0.56 for DZ twins. MZ correlations were significantly higher than DZ correlations (two-tailed p<0.05) for the scotopic mixed flash b-wave implicit time (MZ 0.63; DZ 0.25), photopic flicker amplitudes (MZ 0.77; DZ 0.28)and photopic b-wave amplitudes (MZ 0.77; DZ 0.37) and implicit times (MZ 0.87; DZ 0.56).Higher correlations in MZ twins suggest significant genetic contributions, and this would appear to be more the case for cone-system than rod-system responses. Conversely, this would suggest that the rod system may be more susceptible to environmental modification. This may relate to the greater vulnerability of the rod system in many disease processes.

Where applicable, experiments conform with Society ethical requirements