TGC repeat expansion in the TCF4 gene increases the risk of Fuchs' endothelial corneal dystrophy in Australian cases

This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Fuchs’ endothelial corneal dystrophy (FECD) is a progressive, vision impairing disease. Common single nucleotide polymorphisms (SNPs) and a trinucleotide repeat polymorphism, thymine-guanine-cytosine (TGC), in the TCF4 gene have been associated with the risk of FECD in some populations. We previously reported association of SNPs in TCF4 with FECD risk in the Australian population. The aim of this study was to determine whether TGC repeat polymorphism in TCF4 is associated with FECD in the Australian population. In 189 unrelated Australian cases with advanced late-onset FECD and 183 matched controls, the TGC repeat polymorphism located in intron 3 of TCF4 was genotyped using a short tandem repeat (STR) assay. The repeat length was verified by direct sequencing in selected homozygous carriers. We found significant association between the expanded TGC repeat (≥ 40 repeats) in TCF4 and advanced FECD (P = 2.58 × 10−22; OR = 15.66 (95% CI: 7.79–31.49)). Genotypic analysis showed that 51% of cases (97) compared to 5% of controls (9) were heterozygous or homozygous for the expanded repeat allele. Furthermore, the repeat expansion showed stronger association than the most significantly associated SNP, rs613872, in TCF4, with the disease in the Australian cohort. This and haplotype analysis of both the polymorphisms suggest that considering both the polymorphisms together rather than either of the two alone would better predict susceptibility to FECD in the Australian population. This is the first study to report association of the TGC trinucleotide repeat expansion in TCF4 with advanced FECD in the Australian population

Microbial keratitis predisposing factors and morbidity

PURPOSE: To examine predisposing factors, treatment costs, and visual outcome of microbial keratitis in an ophthalmic casualty and inpatient population. DESIGN: Retrospective medical records review. PARTICIPANTS: Fifteen- to 64-year-olds with microbial keratitis treated at the Royal Victorian Eye and Ear Hospital between May 2001 and April 2003 (n = 291). METHODS: Risk factors were identified from patient files. Demographic, clinical, and microbiological data; severity; outpatient visits; hospital bed days; and vision loss were examined. MAIN OUTCOME MEASURES: Cost to treat (Australian dollars), vision loss, and factors influencing these outcomes. RESULTS: Ocular trauma (106/291 [36.4%]) and contact lens (CL) wear (98/291 [33.7%]) were the most commonly identified predisposing factors; 18 (6.1%) had multiple predisposing factors; 17 (5.8%), ocular surface disease; 20 (6.9%), herpetic eye disease; 4 (1.4%), systemic associations; 5 (1.7%), other; and 23 (7.9%), unknown cause. Of trauma cases, 90.6% involved males, compared with 44% to 57% for other groups (P<0.001). Contact lens wearers were younger than the other groups--mean age 30 years, compared with 40 to 47 years (P<0.01). Gram-negative organisms were isolated more frequently in CL wearers than trauma cases (18.7% vs. 6.5%, P = 0.01). The number of outpatient visits was 4+/-1 (median +/- interquartile range), and 19.6% (57/291) were hospitalized for 5+/-2 days. Hospital resource use and vision loss were similar for predisposing factors but differed by causative microorganism. Eighty-eight percent of cases were scraped: acanthamoeba keratitis was the most expensive to treat, followed by fungal and herpetic keratitis and, lastly, culture-proven bacterial keratitis or culture-negative cases (P<0.0001). After treatment, 21.7% exhibited >2 lines of vision loss, and 1.6% of cases had > or =10 lines of vision loss. Vision loss was associated with clinical severity (P = 0.005). CONCLUSIONS: Ocular trauma and CL wear are the major predisposing factors for microbial keratitis in this age range. These cases require significant hospital resources during treatment, and the keratitis may result in loss of vision

Long-term refractive outcomes and stability after excimer laser surgery for myopia

Purpose: To evaluate the long-term refractive outcomes of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) for myopia. Setting: Centre for Eye Research Australia, Melbourne, Australia. Design: Comparative case series. Methods: Preoperative baseline refractions in eyes having PRK, LASIK, or both at 1 multisurgeon center were analyzed from patient databases. Two- to 13-year follow-up data were analyzed and compared with 1-month postoperative visual outcomes. Results: The study evaluated 389 eyes (229 patients). In the PRK group, the mean preoperative spherical equivalent (SE) was -4.05 diopters (D) ± 1.17 (SD) in eyes with low to moderate myopia and -7.97 ± 2.00 D in eyes with high myopia (P = .009) and in the LASIK group, -3.98 ± 1.27 D and -7.64 ± 1.66 D, respectively (P = .008). At the last visit, the mean SE in the PRK group was -0.64 ± 0.83 D in eyes with low to moderate myopia and -1.06 ± 1.74 D in eyes with high myopia (P = .73) and in the LASIK group, -0.33 ± 0.59 D and -0.63 ± 0.90 D, respectively (P = .68). At the end of the study, 45.9% of eyes with low to moderate myopia and 25.0% with high myopia in the PRK group and 64.8% and 37.3%, respectively, in the LASIK group were within ±0.50 D of the attempted correction. Conclusions: Laser refractive surgery effectively treated all levels of myopia. Refractive stability was achieved within 1 year postoperatively, with LASIK showing better stability than PRK for up to 6 to 9 years

Characteristics of the FECD case and control cohorts, and dichotomised distribution of the <i>TCF4</i> TGC repeat alleles in cases and controls.

<p>The age and sex between cases and controls were compared using the Student’s t-test and chi-square test, respectively. Expanded allele counts between cases and controls were compared using chi-square test.</p

Distribution of genotypes of the <i>TCF4</i> TGC repeat alleles in FECD cases and controls.

<p>The numbers of individuals with each of the three possible genotypes of the dichotomised repeat alleles are shown. S represents short (<40 repeats; non-expanded) and L long (≥40 repeats; expanded) allele. SS represents homozygous non-expanded, LL homozygous expanded, and SL heterozygous with one non-expanded and one expanded allele.</p

Analysis of <i>TCF4</i> TGC repeat polymorphism in homozygous FECD cases and controls.

<p>PCR was performed on genomic DNA from cases and controls carrying the shortest or the longest <i>TCF4</i> TGC repeat length. Data from two representative cases (F-31 and F-137 with 12 and 83 repeats, respectively) and controls (C-62 and C-05, with 12 and 18 repeats, respectively) are shown. <b>A.</b> Agarose gel electrophoresis of the PCR amplified repeat region from homozygous FECD cases and controls. Sizes of the products are shown on the right and correspond with the expected sizes (F-31 and C-62, 265 bp each; F-137, 478 bp; C-05, 283 bp). Sizes of DNA markers are indicated on the left. <b>B.</b> Sequencing chromatograms of FECD-affected (F-31 and F-137) and control (C-62 and C-05) individuals homozygous for the shortest (<b>B.I and B.II</b>) and the longest (<b>B.III and B.IV</b>) repeat alleles are shown. TGC repeat length in each individual was calculated by substracting 230 bps, corresponding to the DNA region flanking the repeat region amplified during PCR, from the detected PCR product size and dividing the difference by 3 (number of nucleotides of the repeat). <b>C-F.</b> Electropherograms showing the sizes of TGC repeat alleles in FECD cases F-31 (<b>C</b>) and F-137 (<b>E</b>) and in two control individuals C-62 <b>(D</b>) and C-05 (<b>F</b>) detected by STR assay. The peaks representing the <i>TCF4</i> TGC repeat fragments are indicated by arrows. Multiple peaks seen in panel E are due to variation in product size when large repeats are amplified. X-axis, fragment sizes in base pairs; Y-axis, relative fluorescence units; orange peaks, sizes of internal standards; red line across the electropherograms, slope threshold for peak start/end.</p

Distribution of TGC repeat lengths in the <i>TCF4</i> gene in FECD cases and controls.

<p>Median repeat length in cases = 53; range: 11–115, and median repeat length in controls = 18; range: 11–83. The box represents the second and third quartiles and the line in the middle indicates median. The lower and upper wiskers represent the limits of the first and fourth quartiles, respectively. The dots represent individual data points for controls (n = 183) and cases (n = 189).</p