The association between VSX1 exon3 gene variants and keratoconus in Malaysian patients.

Purpose: This case-control study aims to examine possible associations of VSX1 exon3 gene variants with the development of keratoconus (KC) in Malaysian patients. Methods: A case-control study was done on 42 keratoconus cases, 127 family member controls, and 96 normal controls. Results: Three gene variants, p.A182A, p.P237P, and p.R217H showed significant associations with keratoconus (P < 0.05). While p.A182A and p.P227P were more prevalent than in the family and normal controls (OR 3.14-4.05), the reverse was observed with p.R217H (OR 0.086-1.59). With Haploview analysis, p.A182A and p.P237P were shown to be in linkage disequilibrium (LD) (LOD (logarithm of the odds score) score of 2.0, r2 of 0.957, and 95% confidence interval (CI) of 0.96-1.00). Conclusion: The study results suggest that the p.A182A and p.P237P variants could have contributed to the development of keratoconus in some Malaysians and that these two variants are likely to be co-inherited. In contrast, the p.R217H variant appeared to confer some protection against the development of keratoconus.

Visual System Homeobox 1 (VSX1) Gene Analysis in Keratoconus: Design of Specific Primers and DNA Amplification Protocols for Accurate Molecular Characterization.

BACKGROUND: Keratoconus is an ocular degeneration characterized by the thinning of corneal stroma that may lead to varying degrees of myopia and visual impairment. Genetic factors have been reported in the pathology of keratoconus where Asians have a higher incidence, earlier onset, and undergo earlier corneal grafts compared to Caucasians. The visual system homeobox 1 (VSX1) gene forms part of a paired-like homeodomain transcription factor which is responsible for ocular development. The gene was marked as a candidate in genetic studies of keratoconus in various populations. Single nucleotide polymorphisms (SNPs) in the VSX1 gene have been reported to be associated with keratoconus. The detection of the SNPs involves DNA amplification of the VSX1 gene followed by genomic sequencing. Thus, the objective of this study aims to establish sensitive and accurate screening protocols for the molecular characterization of VSX1 polymorphisms. METHODS: Keratoconic (n = 74) and control subjects (n = 96) were recruited based on clinical diagnostic tests and selection criteria. DNA extracted from the blood samples was used to genotype VSX1 polymorphisms. In-house designed primers and optimization of PCR conditions were carried out to amplify exons 1 and 3 of the VSX1 gene. PCR conditions including percentage GC content, melting temperatures, and differences in melting temperatures of primers were evaluated to produce sensitive and specific DNA amplifications. RESULTS: Genotyping was successfully carried out in 4 exons of the VSX1 gene. Primer annealing temperatures were observed to be crucial in enhancing PCR sensitivity and specificity. Annealing temperatures were carefully evaluated to produce increased specificity, yet not allowing sensitivity to be compromised. In addition, exon 1 of the VSX1 gene was amplified using 2 different sets of primers to produce 2 smaller amplified products with absence of non-specific bands. DNA amplification of exons 1 and 3 consistently showed single band products which were successfully sequenced to yield reproducible data. CONCLUSIONS: The use of in-house designed primers and optimized PCR conditions allowed sensitive and specific DNA amplifications that produced distinct single bands. The in-house designed primers and DNA amplification protocols established in this study provide an addition to the current repertoire of primers for accurate molecular characterization of VSX1 gene polymorphisms in keratoconus research.