Atlas of Ophthalmology

Patient:  Female, 21 years of age, BCVA 0.7 at OD, 0.3 at OS; IOP 14 mmHg at OD, 14 mmHg at OS. Ocular medical history:  diminishing visual acuity at OS.    General medical history: empty. Main complaint: decreased vision at OS. Purpose:  to present a patient with a bilateral lens opacity. Method: patient undergone examination of anterior segment by Scheimpflug-method (Oculus, Pentacam) and colour photography. Findings: Scheimpflug-method: showing an opacity of the lens nucleus Colour photography: depicting a bilateral opacity of the lens nucleus. Discussion: Congenital cataract is a leading cause of childhood blindness, accounting for 10~38% of blindness in children. The prevalence of congenital cataract is estimated to be 0.6~6 per 10,000 live births (1). Various etiological factors have been reported, including infection, neonatal asphyxia, malnutrition, and genetic defects. 8.3%~25% of congenital cataracts were inherited. Several genes have been identified to be associated with congenital cataracts, such as genes encoding crystallins, connexins and other membrane proteins, beaded filament proteins, growth and transcription factors, and others. The crystallins are the main structural proteins of the eye lens (2). The alphaA-crystallin is a molecular chaperone. It is expressed mainly in the lens. Mutations in the Cryaa gene lead to recessive or dominant cataracts. Altered gamma-crystallins is a key event in cataract formation. Cataract formation, caused by Cryg mutations is characterized by stopping the secondary lens fiber differentiation as indicated by the presence of remnants of cell nuclei, which are usually degraded in secondary fiber cells. One of several molecular mechanism underlying the congenital hereditary cataract is caused by the recently characterized A2V mutation in βB2-crystallin. It was reported (3) that the tetramerization of βB2-crystallin was retarded by the A2V mutation. They showed, that the A2V-mutation slightly decreased the thermal stability and promoted the thermal aggregation of βB2-crystallin. A2V mutation lead to injury of lens optical properties by decreasing βB2-crystallin stability. The minor changes by the A2V mutation was consistent with the phenotype in the patients, who noticed their optical defects at the twenties. As age increased, damages in βB2-crystallin would accumulate by the unavoidable physical and chemical stresses. The slight decrease in thermal stability of the mutated βB2-crystallin finally led to the onset of cataract much earlier than normal people, but later than those highly harmful mutations. Literature: (1) Wilson ME, Pandey SK, Thakur J. Paediatric cataract blindness in the developing world: surgical techniques and intraocular lenses in the new millennium. Br J Ophthalmol. 2003;87:14–9. (2) Graw J. Genetics of crystallins: cataract and beyond. Exp Eye Res. 2009 Feb;88(2):173-89. (3) Xu J, Wang S, Zhao W-J, Xi Y-B, Yan Y-B, et al. (2012) The Congenital Cataract-Linked A2V Mutation Impairs Tetramer Formation and Promotes Aggregation of βB2-Crystallin. PLoS ONE 7(12): e51200.

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