Report of ocular features including retinal photoreceptor degeneration associated with a novel unbalanced chromosomal translocation (6:12)(p21.1;p13) in an infant.

Abstract

Abstract: : Purpose:Report of ocular features including retinal photoreceptor degeneration associated with a novel unbalanced chromosomal translocation (6:12)(p21.1;p13) in an infant. Methods:Case report of KS, the 1.85 kg product of a full–term gestation to a 37 year old G4, P1, Ab2, healthy mother. An unbalanced translocation was identified on amniocentesis, with the karyotype 46 XX, der(12)t(6:12)(p21.1;p13) and confirmed on postnatal analysis. A complete eye examination, ocular ultrasonography and electroretinogram were performed. Results:Ophthalmologic abnormalities included nystagmus, severe bilateral ptosis, high myopia, optic nerve hypoplasia, and a decreased foveal reflex with macular granularity. On ocular ultrasonography, the globes had normal axial length; a vitreous strand extended to the right optic nerve head and a moderate amount of fluid surrounded each optic nerve. An electroretinogram was done under general anesthesia and demonstrated reduction in both scotopic and photopic amplitudes. Scotopic amplitudes were decreased by seventy percent on the right and fifty percent on the left; photopic amplitudes were decreased by thirty percent on the right and twenty percent on the left. Conclusions:The unbalanced translocation (partial duplication of 6p and partial monosomy 12p) in this patient is unique. Previously reported ocular features of a partial duplication of 6p include ptosis and microphthalmia; partial monosomy12p does not have a defined phenotype and is generally a lethal abnormality. New ocular features in this patient include nystagmus, photoreceptor degeneration, optic nerve hypoplasia and high myopia. Microphthalmia, reported in other duplication 6p cases, was not present in this patient. The electroretinogram was abnormal and characteristic of an early rod–cone dystrophy or a generalized metabolic abnormality. A review of the online human genome via the National Center for Biotechnology Information integrated website revealed several candidate genes expressed in retinal tissue in the regions of the 6p21.1 and 12p13 chromosomal breakpoints, including RBP5 (retinol binding protein 5, cellular), RDS (retinal degeneration, slow), GUCA1A (guanylate cyclase activator 1A), and GUCA1B (guanylate cyclase activator 1B). We postulate that the chromosomal break points (6p21.1 and 12p13) span a gene expressed in the retina causing the photoreceptor degeneration.

Keywords: retina • electroretinography: clinical • genetics