Biomedical subjects

Maurice K H Yap

Publications and source records attributed to Maurice K H Yap.

5 recordsLinked to original sources

PubMed2006

Family-based association analysis of hepatocyte growth factor (HGF) gene polymorphisms in high myopia.

PURPOSE: To investigate the association of high myopia with polymorphisms in the hepatocyte growth factor (HGF) gene, a potential candidate for myopia development. METHODS: Single nucleotide polymorphisms (SNPs) were screened and identified in the HGF gene region with denaturing high-performance liquid chromatography, and their linkage disequilibrium pattern was established in a Han Chinese population (n=150). Tag SNPs were selected and genotyped using restriction digestion and fluorescence polarization assays for 128 nuclear families with 133 severely myopic (mean spherical equivalent [MSE]<or=-10.0 D) offspring. A family-based association study was performed using FBAT and GenAssoc (Cambridge University, Cambridge, UK). RESULTS: Of three tag SNPs (HGF5-5b, HGFe9, and HGFe10b) selected for association study, HGF5-5b, located in the upstream region, was found to be associated with high myopia considered as a quantitative trait (MSE) in additive, dominant, and recessive models (P=0.0157, 0.0108, and 0.0108, respectively). The genotype relative risk was 2.19 for the genotype C/T, and 2.14 for T/T with reference to C/C of HGF5-5b. Significantly reduced transmission was demonstrated for the haplotypes C-A-C (HGF5-5b, HGFe9, and HGFe10b; P=0.0031) and C-A (HGF5-5b and HGFe9; P=0.0015) in the recessive model, whereas significantly increased transmission was found for haplotype T-C (HGF5-5b and HGFe10b; P=0.0040) under the dominant model. Preferential transmission of haplotypes remained significant even after correction for multiple comparisons. Analysis gave similar results, with myopia considered to be a qualitative trait. CONCLUSIONS: HGF is a potential locus associated with high myopia in the Han Chinese population. This is the first study reporting the association of an HGF gene polymorphism with high myopia.

Adult↗

PubMed2006

[Establishing the linkage disequilibrium pattern for the all-trans-retinol dehydrogenase (RDH8) gene].

OBJECTIVE: As part of an on-going effort to map genes involved in complex eye diseases, myopia in particular, single nucleotide polymorphisms (SNPs) and linkage disequilibrium (LD) pattern were used to identified the gene within and around the All-trans-retinol dehydrogenase (RDH8). METHODS: Denaturing high-performance liquid chromatography (DHPLC) was used to screen SNPs in 4 DNA pools each consisting of DNA from five individuals, and genotypes identified SNPs coupled with DNA pooling strategy were performed in 150 Chinese subjects from Hong Kong. The identified common SNPs were included in LD and haplotype analysis using the Haploview2.05 and EH programs. RESULTS: Fifteen SNPs were identified: 7 were common with the minor allele frequency > 0.05, and 10 were novel. Four SNPs in the 3' region exhibited significant LD (/|D'/ > 0.75 and its confidence interval suggesting strong LD, r2 > 0.33, P < 0.031) and formed a haplotype block while 3 common SNPs in the 5' region did not exhibit obvious LD. CONCLUSION: The block-like LD pattern existed around the RDH8 gene region suggest that one SNP (RDH8E5a probably) in the 3' region and at least 2 SNPs in the 5' region (RDH851 particularly) were needed in association studies involving RDH8.

Alcohol Oxidoreductases↗

PubMed2005

Retinal stretching limits peripheral visual acuity in myopia.

Axial elongation of the myopic eye has the potential to stretch the retina, thereby reducing the sampling density of retinal neurons. Resolution acuity in the peripheral field of normal eyes is known to be sampling-limited, which suggests that retinal stretching in the myopic eye should have a direct effect on resolution acuity everywhere in the visual field except perhaps the fovea, which is usually optically limited. We tested this prediction that neural sampling density is reduced in myopic eyes by measuring resolution acuity for sinusoidal gratings in the fovea plus five peripheral locations in 60 myopic subjects exhibiting a wide range of refractive errors. Control experiments using a detection paradigm to provoke spatial aliasing verified that peripheral resolution was sampling limited. Retinal spatial frequencies of the grating stimulus were computed assuming Knapps' Law of visual optics, which ensures that retinal image size (in mm) is independent of refractive error when axial myopia is corrected by a spectacle lens located in the anterior focal plane of the eye. Results obtained at every retinal locus showed that resolution acuity declined linearly with magnitude of refractive error. Regression of the population data indicated that approximately 15 D of refractive error doubles the spacing between retinal neurons, thereby halving peripheral resolution acuity relative to the emmetropic eye. Several subjects also demonstrated sampling-limited performance in the fovea, which indicated that optical filtering by the eye's optical system failed to protect the fovea from aliasing artifacts of neural undersampling in these eyes. We conclude that stretching of the retina is a primary cause of reduced spatial resolution of the peripheral field, and occasionally of the fovea, in myopic eyes. Stretching appears to be locally uniform over the central +/-15 degrees of visual field but is globally non-uniform since the foveal region appears to stretch more than the globe itself.

Adult↗

PubMed2004

Macular pigment optical density in young Chinese adults.

PURPOSE: The purpose of this study was to determine the macular pigment optical density (MPOD) in a group of Chinese subjects using a simple customized light emitting diode-based device. METHODS: Heterochromatic flicker photometry was used in this study. With a 1 degrees diameter circular test stimulus, MPOD was estimated by comparing the relative sensitivities to a blue light, against a green reference, between foveal and parafoveal 4 degrees temporal locations. Fixed alternating frequencies were used. Repeatability was determined on a small group of subjects. A further group of 67 young healthy subjects provided data for MPOD norms. RESULTS: All results were corrected to the common MPOD reference wavelength of 460 nm. The group-averaged MPOD was 0.48 (S.D. 0.23). We found no gender difference in MPOD. The coefficient of variability was 7.2-8.0% and the coefficient of repeatability was 0.12. CONCLUSIONS: The MPOD of Chinese subjects did not differ greatly from the reported MPOD in white subjects.

Adolescent↗

PubMed2003

Using denaturing HPLC for SNP discovery and genotyping, and establishing the linkage disequilibrium pattern for the all-trans-retinol dehydrogenase (RDH8) gene.

All-trans-retinol dehydrogenase (RDH8) is a visual cycle enzyme that reduces all-trans-retinal to all-trans-retinol. As part of an on-going effort to map genes involved in complex eye diseases, myopia in particular, using association studies, single nucleotide polymorphisms (SNPs) were identified and linkage disequilibrium (LD) pattern was established within and around the RDH8 gene. We used denaturing high-performance liquid chromatography (DHPLC) to screen SNPs in four DNA pools each consisting of DNA from five individuals and genotyped the identified SNPs in 150 Chinese subjects from Hong Kong. Fifteen SNPs were identified: seven were common with the minor allele frequency >0.05 and ten were novel. Common SNPs were included in LD and haplotype analysis using the ASSOCIATE and EH programmes. Four SNPs in the 3' region exhibited significant LD and formed a haplotype block, while three common SNPs in the 5' region did not exhibit useful LD. The LD pattern around the RDH8 gene suggested that one SNP from the 3'region and two to three SNPs from the 5' region were needed in association studies involving RDH8. Our results demonstrated the efficiency of DHPLC in screening SNPs when coupled with DNA pooling strategy and in genotyping SNPs.

Alcohol Oxidoreductases↗