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Daniel Gratie, Edwin Stone, Jade East, Robert Mullins, Arlene Drack; Mutation analysis in patients suspected to have PAX6-related ocular malformations. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5690.
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To determine the frequencies of specific mutations and genotype-phenotype correlations in a cohort of patients with typical or suspected aniridia.
DNA was extracted from whole blood using Gentra Systems’ Autopure LS instrument. 12 ½ micrograms of DNA from each patient were used as template in 8.35µl polymerase chain reactions (PCR). Amplification products were denatured for 3 minutes at 94 degrees C and electrophoresed on 6% polyacrylamide, 5% glycerol gels at 25W for approximately 3 hours at room temperature. Following electrophoresis, gels were stained with silver nitrate. Abnormal PCR products identified by SSCP analysis were confirmed using automated DNA sequencing with dye termination chemistry on an ABI 3730 sequencer. All sequencing was bi-directional.Retrospective chart review was performed to collect clinical data and all tabulated information was anonymized.
Of the 79 probands samples referred for PAX6 testing, 66 had sufficient DNA for full gene analysis. Disease-causing mutations were identified in 31/66 (47%). 94% of these individuals had aniridia as their original diagnosis; the remainder had either ocular albinism or nystagmus. Mutations were found in exons 4-11 and 13. The mutation frequency distribution was 32% exon 5, 16% exon 7, 13% exon 6, 10% exon 8, 10% exon 10, 6% exon 13, 3% exons 4, 9 or 11. No mutations were found in exon 12. Family member samples were available for 4 probands yielding 11 members of 4 multigenerational families. Mutations in exons 5 or 7 were the most likely to have a variable iris phenotype rather than typical aniridia. Iris phenotypes included diffuse transillumination defects, elliptical iris anomaly, iris coloboma, and pupillary notching. Expressivity was variable, however presence or absence of congenital visually significant cataracts and glaucoma were highly penetrant.
PAX6 mutations cause a host of ocular malformations, many of which are not immediately recognizable clinically as aniridia. Study of the phenotypes associated with mutations in different exons may lead to better understanding of the function of specific domains, and possibly to the development of specific treatments. PAX6 exons 5 and 7 are hotspots for variable iris phenotypes. References: http://lsdb.hgu.mrc.ac.uk/home.php?select_db=PAX6; ; Sharan S et al. JAAPOS 2008;12(4):340-3.; Netland PA et al. JAAPOS 2011;15(6):562-6.
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