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A. Santana, Sr., M. Waiswol, E. S. Arcieri, F. Richeti, J. P. C. Vasconcellos, M. B. Melo; Mutation (TYR56STOP) in the Gamma D-Crystallin Gene Causing Autosomal Dominant Congenital Cataract in a Brazilian Family. Invest. Ophthalmol. Vis. Sci. 2008;49(13):450.
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Congenital cataracts are one of the most treatable causes of visual impairment and blindness during infancy, with an estimated prevalence of 1 to 6 cases per 10,000 live births. All three types of Mendelian inheritance have been reported for cataract; however, autosomal dominant transmission seems to be the most frequent. There is an intimate relation between crystallin genes and lens transparency, and therefore they are excellent candidate genes for inherited cataract. The purpose of this study was to investigate mutations in the alpha A, gamma C and gamma D-crystallin genes (CRYAA, CRYGC and CRYGD, respectively) in a Brazilian family with autosomal nuclear cataract.
A two-generation Brazilian family, composed of three affected and two unaffected individuals, was referred to Santa Casa de São Paulo Ophthalmology Departament. The coding regions and intron/exon boundaries of the CRYAA, CRYGC and CRYGD genes were amplified by PCR and directly sequenced.
Sequenced analysis of the CRYAA and CRYGC genes excluded possible mutations, but identified polymorphisms already reported. Sequence analysis of the CRYGD gene revealed, in exon 2, a point mutation leading to the substitution of a tyrosine for a stop codon at amino acid 56 (TYR56STOP). This missense mutation obliterated a restriction site for the enzyme MslI, that segregated with all affected members in the family, but was not detected in 50 unrelated normal controls and unaffected members.
We have identified, in the gamma D-crystallin gene, a mutation causing congenital nuclear cataract in a Brazilian family, which, to our knowledge, is being reported for the first time. This premature stop codon occurring at amino acid 56 results in a truncated protein missing 118 amino acids.
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