Calvin Pang

Lipid peroxidation in cord blood at birth

OBJECTIVE The purpose of this study was to determine oxygen free radical activity in the neonate at birth and relate it to umbilical cord blood acid-base status. STUDY DESIGN A series of 110 singleton deliveries had determination of two lipoperoxides in umbilical cord blood: malondialdehyde and organic hydroperoxide. Umbilical pH, PO2, PCO2, bicarbonate, and base excess were also measured. RESULTS There was a significant association between lipoperoxides and cord blood pH and base excess. A significant difference existed in the levels of umbilical artery lipoperoxides between nonacidemic and acidemic fetus, as defined by an umbilical arterial pH < 7.20. CONCLUSION There is a positive association between lipoperoxide production and acid-base balance at delivery.

Frequency of the fragile X syndrome in Chinese mentally retarded populations is similar to that in Caucasians

Fragile X syndrome is recognized as the most common inherited cause of mental retardation in western countries. The prevalence of the fragile X syndrome in Asian populations is uncertain. We report a multi-institutional collaborative study of molecular screening for the fragile X syndrome from 1,127 Chinese mentally retarded (MR) individuals. We found that 2.8% of the Chinese MR population screened by DNA analysis had the fragile X full mutation. Our screening indicated that the fragile X syndrome prevalence was very close to that of Caucasian subjects. In addition, we found that 62.5% of fragile X chromosomes had a single haplotype for DXS548-FRAXAC1 (21-18 repeats) which was present in only 9.7% of controls. This unique distribution of microsatellite markers flanking the FMR1 CGG repeats suggests that the fragile X syndrome in Chinese populations, as in the Caucasian, may also be derived from founder chromosomes.

Oxygen free radical activity in the second stage of labor

Objective. To assess fetal cellular injury arising from oxygen free radical activity in relation to the duration of the second stage of labor.

A survey of FRAXE allele sizes in three populations

FRAXE is a fragile site located at Xq27-8, which contains polymorphic triplet GCC repeats associated with a CpG island. Similar to FRAXA, expansion of the GCC repeats results in an abnormal methylation of the CpG island and is associated with a mild mental retardation syndrome (FRAXE-MR). We surveyed the GCC repeat alleles of FRAXE from 3 populations. A total of 665 X chromosomes including 416 from a New York Euro-American sample (259 normal and 157 with FRAXA mutations), 157 from a Chinese sample (144 normal and 13 FRAXA), and 92 from a Finnish sample (56 normal and 36 FRAXA) were analyzed by polymerase chain reaction. Twenty-seven alleles, ranging from 4 to 39 GCC repeats, were observed. The modal repeat number was 16 in the New York and Finnish samples and accounted for 24% of all the chromosomes tested (162/665). The modal repeat number in the Chinese sample was 18. A founder effect for FRAXA was suggested among the Finnish FRAXA samples in that 75% had the FRAXE 16 repeat allele versus only 30% of controls. Sequencing of the FRAXE region showed no imperfections within the GCC repeat region, such as those commonly seen in FRAXA. The smaller size and limited range of repeats and the lack of imperfections suggests the molecular mechanisms underlying FRAXE triplet mutations may be different from those underlying FRAXA.

Oxidative stress in the fetal lamb brain following intermittent umbilical cord occlusion: a path analysis

Objective To evaluate the relative contribution of cord occlusion length intervals between occlusions and experimental duration on oxidative stress in the fetal lamb brain.

Genome-wide association study identifies WNT7B as a novel locus for central corneal thickness in Latinos

The cornea is the outermost layer of the eye and is a vital component of focusing incoming light on the retina. Central corneal thickness (CCT) is now recognized to have a significant role in ocular health and is a risk factor for various ocular diseases, such as keratoconus and primary open angle glaucoma. Most previous genetic studies utilized European and Asian subjects to identify genetic loci associated with CCT. Minority populations, such as Latinos, may aid in identifying additional loci and improve our understanding of the genetic architecture of CCT. In this study, we conducted a genome-wide association study (GWAS) in Latinos, a traditionally understudied population in genetic research, to further identify loci contributing to CCT. Study participants were genotyped using either the Illumina OmniExpress BeadChip (∼730K markers) or the Illumina Hispanic/SOL BeadChip (∼2.5 million markers). All study participants were 40 years of age and older. We assessed the association between individual single nucleotide polymorphisms (SNPs) and CCT using linear regression, adjusting for age, gender and principal components of genetic ancestry. To expand genomic coverage and to interrogate additional SNPs, we imputed SNPs from the 1000 Genomes Project reference panels. We identified a novel SNP, rs10453441 (P = 6.01E-09), in an intron of WNT7B that is associated with CCT. Furthermore, WNT7B is expressed in the human cornea. We also replicated 11 previously reported loci, including IBTK, RXRA-COL5A1, COL5A1, FOXO1, LRRK1 and ZNF469 (P < 1.25E-3). These findings provide further insight into the genetic architecture of CCT and illustrate that the use of minority groups in GWAS will help identify additional loci.

Additive effect of aldose reductase Z-4 microsatellite polymorphism and glycaemic control on cataract development in type 2 diabetes

AIMS To examine the additive effect of the z-4 microsatellite polymorphism of aldose reductase gene (ALR2) and glycaemic control on risk of cataract in a prospective cohort of Chinese type 2 diabetic patients. METHODS The (CA)n microsatellite polymorphism of ALR2 was determined using PCR followed by capillary gel electrophoresis. Cataract was defined by presence of lens opacity on direct ophthalmoscopy or history of cataract surgery. A non-linear curve approach was used to identify the threshold of glycated hemoglobin (HbA1c) at which the odds ratio (OR) for cataract started to increase. The association of z-4 allele with cataract, above and below this threshold, was assessed using multiple logistic regression analysis. RESULTS Of the 5823 patients analyzed, 28.1% had cataracts. After adjusting for conventional risk factors and using non-z-4 carriers with HbA1c<8.0% as referent group (n = 3173), the OR (95% confidence intervals) for cataract was highest in z-4 carriers with HbA1c ≥ 8.0% [1.43 (1.05-1.96), n = 244], compared to non-z-4 carriers with HbA1c ≥ 8.0 [1.27 (1.10-1.47), n = 1836] and z-4 carriers with HbA1c<8.0%[1.01 (0.77-1.29), n = 420, P(trend) < 0.001]. This additive association remained significant after additional adjustments for drug use (P(trend) = 0.002) and renal function (P(trend) = 0.01). CONCLUSIONS In type 2 diabetic patients with suboptimal glycaemic control, the z-4 allele of ALR2 (CA)n polymorphism was independently associated with increased susceptibility to cataracts.

Systems genetics identifies a role for Cacna2d1 regulation in elevated intraocular pressure and glaucoma susceptibility

Glaucoma is a multi-factorial blinding disease in which genetic factors play an important role. Elevated intraocular pressure is a highly heritable risk factor for primary open angle glaucoma and currently the only target for glaucoma therapy. Our study helps to better understand underlying genetic and molecular mechanisms that regulate intraocular pressure, and identifies a new candidate gene, Cacna2d1, that modulates intraocular pressure and a promising therapeutic, pregabalin, which binds to CACNA2D1 protein and lowers intraocular pressure significantly. Because our study utilizes a genetically diverse population of mice with known sequence variants, we are able to determine that the intraocular pressure-lowering effect of pregabalin is dependent on the Cacna2d1 haplotype. Using human genome-wide association study (GWAS) data, evidence for association of a CACNA2D1 single-nucleotide polymorphism and primary open angle glaucoma is found. Importantly, these results demonstrate that our systems genetics approach represents an efficient method to identify genetic variation that can guide the selection of therapeutic targets.Elevated intraocular pressure (IOP) is a heritable risk factor for primary open angle glaucoma. Using forward mouse genetics, cell biology, pharmacology and human genetic data, the authors identify CACNA2D1 as an IOP risk gene that can be therapeutically targeted by the drug pregabalin in animal models.

Molecular and Clinical Genetics of Retinoblastoma

Retinoblastoma (RB) is the most common intraocular cancer in children affecting all populations. Prognosis is highly dependent on the timing of diagnosis. Late presentation with extraocular spread is often fatal. In contrast, early-staged diseases are mostly curable using systemic plus focal therapy. Therefore, early presymptomatic diagnosis and even prenatal diagnosis are crucial to improve the clinical outcome. In recent years extensive studies on the RB1 gene and other RB-related genes have contributed to the better understanding of the disease mechanism. Inactivation of both copies of the RB1 gene on chromosome 13q14, due to loss-of-function mutations, is a prerequisite for tumorigenesis in RB. Secondary genetic alterations, such as lesions in another gene, are necessary to precipitate tumour development. We have found in Hong Kong Chinese about 19% of RB patients carry a germ-line RB1 mutation with no methylation at the RB1 promoter. We detected inactivation of the RB1 gene by loss-of-function mutations and loss of heterozygosity (LOH), but rarely by promoter hypermethylation, in Chinese sporadic RB. Promoter hypermethylation that silences gene expressions in the tumour suppressor gene RASSF1A and the DNA repair genes MGMT and MLH1 is a causative factor of retinoblastoma. We have also revealed the presence of microsatellite instability and recurrent loss of heterozygosity at multiple chromosomal regions in the retinoblastoma genome, showing genes other than RB1 as primary or secondary cause of retinoblastoma. Recently, we are working on extraocular regulation of RB development. Our studies on Chinese RB samples have led to useful information in the RB genome and cell biology for novel design of therapeutic modalities for RB.

Revisiting the Trabecular Meshwork in the Eyes of the Developing Human

Background: The trabecular meshwork (TM) is a specialized tissue which is crucial to maintain ocular health (e.g. intraocular pressure) and to sustain optical clarity. Since collagen and elastic fibers are the primary structural components of the tissue, the characterization of these fibers in the fetal eye would advance our understanding of the basic morphology and further congenital studies related to the TM. Aims: To reveal the early development of the human fetal TM. Results: The results showed the presence of circular (radial) and longitudinal collagen fibers as well as trabecular cells in the TM by 12 weeks of gestation. By 26 weeks, the venous system connected with Schlemm’s canal and thin elastic fibers began to form. At birth, longitudinal collagen fibers linked with each other to form long strands. There was also evidence of an increase in circular (or radial) collagen fibers in the TM. Conclusion: The present study characterized the developmental and morphological changes in the genesis of the fetal TM in terms of growth in collagen and elastic fibers. The elastic fibers were found to exist in small quantity at birth, and, thus, any increase in these fibers to maturity is likely to occur after birth.