Ocular Genetics

Myopia: Heritability and modelling

Spherical equivalent and biometric traits were obtained from 120 myopia families collected through the Genes in Myopia (GEM) study. The results indicated that variance could be attributed to both genetic and environmental components for spherical equivalent whereas for axial length a substantial proportion of the variance was due to genes. Model fitting for both traits indicated that an additive, common and unique environmental model best fitted the data.

Linkage analysis

Three of the larger families collected as part of the GEM study were genotyped. The largest family contains 35 people with 18 affected with myopia. Linkage analysis followed by fine mapping has allowed us to narrow the myopia gene containing region to 0.8cM (~ 800,000 base pairs) on chromosome 2 in these families. Six known genes and 6 hypothetical genes have been identified in this region.

SNP analysis of the MYP2 region

Sixty single nucleotide polymorphisms (SNP’s) have been genotyped across 150 hypermetropes, 150 emmetropes, 150 low/moderate myopes and 150 high myopes of the Myopia-2 locus (MYP2) on chromosome 18p11. Association analysis was undertaken on 2 candidate genes in a myopia-linked region on chromosome 18 but no association was evident.

Myopia twin studies

Twin analysis on 620 twin pairs is now complete. A number of papers are being written up resulting from this analysis.

Quantitative trait linkage analysis (QTL) in twins

Four regions of the genome, previously identified as myopia QTL regions were genotyped. Analysis of our data did not replicate the QTL regions for refraction nor implicate them in biometric measures.

Personality and myopia

The International Personality Item Pool (IPIP) questionnaire was conducted on 633 twin and 278 members from myopia families in the GEM study. Analysis revealed that the personality traits of introversion and conscientiousness were not associated with myopia dispelling the stereotyped image that currently exists for myopia.

SNP analysis of other candidate genes

Association of SNPs in 2 candidate genes was undertaken in our myopia case control cohort. We identified two SNPs in one candidate gene that were associated with low/ moderate myopia. Further sequencing of this gene identified eight other SNPs that showed segregation of variants with myopia. Further analysis is underway in a larger cohort to confirm our findings. The second candidate gene showed no association.

Age-related macular disease: Protein expression studies in AMD eyes

Donor eye tissue continues to be collected and sections from donor eyes have undergone immuno-histochemical analysis and western blotting for a range of antibodies against proteins typically associated with neurodegenerative disorders including Alzheimer’s disease. Analysis of these samples is ongoing.

Analysis of the complement factor H gene

The recently described Y402H change in the complement factor H (CFH) gene of the alternative complement pathway was examined using the Mass Array System of the Australian Genome Research Facility in our collection of AMD patients. Extension of this analysis to include other single nucleotide polymorphisms (SNP) within this gene has revealed a number of risk and protective haplotypes for this gene. Characterisation of SNPs in our different study cohorts including AMD progression, twins and AMD families is ongoing. Genotype/ phenotype analysis is also underway. The interaction of the pathogen Chlamydia pneumoniae with Y402H was also undertaken and significant interaction identified in AMD progression patients. A novel technique of using repeat motifs to determine risk of AMD at the CFH region is also being explored with Genetic Technologies Ltd and the C.Y. O’Connor ERADE Foundation in Perth.

Analysis of SNPs in the RDS gene

The RDS gene is a candidate gene for involvement in AMD due to its role in a number of other retinal diseases. However, we found no association of SNPs in this gene with AMD.

Analysis of SNPs in the VEGF gene

Vascular endothelial growth factor (VEGF) is thought to be a major player in the stimulus of abnormal growth of blood vessels that might be involved in AMD. We undertook an association study using SNPs in this gene but did not find any association with AMD.

Analysis of SNPs in other AMD genes

An analysis of SNPs in a number of AMD disease associated genes including the CFH, BF, C2, PRSS, LOC. PLEK and CFHR1-5 genes is being undertaken in case control, progression and twin cohorts. A DEST funded Australia – India collaborative grant with the LVP Eye Institute in Hyderabad will assess these findings in an AMD biochip.

Linkage analysis in AMD families

Three of our largest AMD families, each with a minimum of eight affected individuals have undergone whole genome scan analysis. Two gene regions have been identified through genetic linkage studies and are being fine mapped in these and other AMD families to narrow the regions of interest in order to uncover disease genes.

Twin analysis

340 twin pairs over the age of 50 years have been recruited and examined through the Australian Twin Registry. A questionnaire, eye exam and DNA sample have been taken from each twin. Psychophysical and phenotypic features have been assessed and statistical analysis is ongoing.

Proteomic analysis of AMD

Proteomic analysis has been undertaken in people with different APOE genotypes. Both cases and controls have been compared to assess differences on 2D gels, Mass spectrometry and DIGE to identify candidate biomarkers in disease. A number of protein changes have been identified between cases and controls and extension of this project to collect other