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Cone dystrophy phenotype associated with a frameshift mutation (M280fsX291) in the -subunit of cone specific transducin (GNAT2)

¹ Institute of Ophthalmology, University College London, 11–43 Bath Street, London EC1V 9EV, UK
² Section of Medical and Molecular Genetics, Department of Paediatrics and Child Health, University of Birmingham, Edgbaston, Birmingham B15 2TT, and West Midlands Regional Genetics Service, Birmingham Women’s Hospital, Birmingham B15 2TG, UK
³ Moorfields Eye Hospital, City Road, London EC1V 2PD, UK
⁴ Department of Experimental Psychology, University of Cambridge, Downing Street, Cambridge CB2 3EB, UK

Correspondence to:
Correspondence to:
Professor A T Moore
Institute of Ophthalmology, University College London, 11–43 Bath Street, London, EC1V 9EL, UK; tony.moore{at}ucl.ac.uk

ABSTRACT
Aim: To describe the phenotype of a three generation consanguineous Pakistani family containing six individuals with autosomal recessive cone dystrophy caused by mutation in GNAT2.

Methods: Five of the six affected individuals underwent an ophthalmological examination, electrodiagnostic testing, fundus photography, autofluorescence imaging, and detailed psychophysical testing.

Results: All five examined patients had a history of nystagmus from infancy, photophobia, defective colour vision, and poor visual acuity. The nystagmus in three of the individuals had lessened with time. Fundus examination revealed an abnormal foveal appearance, without frank atrophy or pigmentation. Electroretinography (ERG) revealed absent ISCEV cone flicker ERGs with some preservation of responses to short wavelength stimulation. Rod ERGs showed no definite abnormality, but maximal (mixed rod-cone) response a-wave amplitudes were mildly subnormal. Rudimentary residual colour vision was detected in three individuals. There is clinical evidence of progressive visual acuity reduction in two older individuals.

Conclusion: Mutation in the -subunit of cone specific transducin (GNAT2) is characterised by an infantile onset cone dystrophy. Some affected individuals may show deterioration of visual acuity with time.

Keywords: cone dystrophy; phenotype; transducin

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