Qingjiong Zhang

Bietti Crystalline Corneoretinal Dystrophy Is Caused by Mutations in the Novel Gene CYP4V2

Bietti crystalline corneoretinal dystrophy (BCD) is an autosomal recessive retinal dystrophy characterized by multiple glistening intraretinal crystals scattered over the fundus, a characteristic degeneration of the retina, and sclerosis of the choroidal vessels, ultimately resulting in progressive night blindness and constriction of the visual field. The BCD region of chromosome 4q35.1 was refined to an interval flanked centromerically by D4S2924 by linkage and haplotype analysis; mutations were found in the novel CYP450 family member CYP4V2 in 23 of 25 unrelated patients with BCD tested. The CYP4V2 gene, transcribed from 11 exons spanning 19 kb, is expressed widely. Homology to other CYP450 proteins suggests that CYP4V2 may have a role in fatty acid and steroid metabolism, consistent with biochemical studies of patients with BCD.

Functions of the intermediate filament cytoskeleton in the eye lens

Intermediate filaments (IFs) are a key component of the cytoskeleton in virtually all vertebrate cells, including those of the lens of the eye. IFs help integrate individual cells into their respective tissues. This Review focuses on the lens-specific IF proteins beaded filament structural proteins 1 and 2 (BFSP1 and BFSP2) and their role in lens physiology and disease. Evidence generated in studies in both mice and humans suggests a critical role for these proteins and their filamentous polymers in establishing the optical properties of the eye lens and in maintaining its transparency. For instance, mutations in both BFSP1 and BFSP2 cause cataract in humans. We also explore the potential role of BFSP1 and BFSP2 in aging processes in the lens.

Novel locus for X linked recessive high myopia maps to Xq23–q25 but outside MYP1

Background: High myopia is a common genetic variation in most cases, affecting 1–2% of people, and is the fourth most common disorder causing blindness worldwide. Six autosomal dominant loci and one X-linked recessive locus have been reported, but no genes responsible for high myopia have been identified. Objective: To report a Chinese family in which six males presented with high myopia consistent with an X linked recessive trait. Results: Affected individuals shared three common features: high myopia, reduced visual acuity, and fundal changes of high myopia. Protan and deutan were observed in the family, but they did not co-segregate with the high myopia phenotype. X-chromosome-wide linkage analysis mapped the high myopia locus to a 25 cM (14.9 Mb) region on Xq23–q25 between DXS1210 and DXS8057, with maximum two point lod scores at θ = 0 of 2.75 and 2.29 for DXS1001 and DXS8059, respectively. Conclusions: This new myopia locus is outside the linked region of the first high myopia locus (MYP1). Refinement of the linkage region with additional families and screening candidate genes for mutation may lead to the identification of the defect gene.

Detection of Variants in 15 Genes in 87 Unrelated Chinese Patients with Leber Congenital Amaurosis

Background Leber congenital amaurosis (LCA) is the earliest onset and most severe form of hereditary retinal dystrophy. So far, full spectrum of variations in the 15 genes known to cause LCA has not been systemically evaluated in East Asians. Therefore, we performed comprehensive detection of variants in these 15 genes in 87 unrelated Han Chinese patients with LCA. Methodology/Principal Findings The 51 most frequently mutated exons and introns in the 15 genes were selected for an initial scan using cycle sequencing. All the remaining exons in 11 of the 15 genes were subsequently sequenced. Fifty-three different variants were identified in 44 of the 87 patients (50.6%), involving 78 of the 88 alleles (11 homozygous and 56 heterozygous variants). Of the 53 variants, 35 (66%) were novel pathogenic mutations. In these Chinese patients, variants in GUCY2D are the most common cause of LCA (16.1% cases), followed by CRB1 (11.5%), RPGRIP1 (8%), RPE65 (5.7%), SPATA7 (4.6%), CEP290 (4.6%), CRX (3.4%), LCA5 (2.3%), MERTK (2.3%), AIPL1 (1.1%), and RDH12 (1.1%). This differs from the variation spectrum described in other populations. An initial scan of 55 of 215 PCR amplicons, including 214 exons and 1 intron, detected 83.3% (65/78) of the mutant alleles ultimately found in these 87 patients. In addition, sequencing only 9 exons would detect over 50% of the identified variants and require less than 5% of the labor and cost of comprehensive sequencing for all exons. Conclusions/Significance Our results suggest that specific difference in the variation spectrum found in LCA patients from the Han Chinese and other populations are related by ethnicity. Sequencing exons in order of decreasing risk is a cost-effective way to identify causative mutations responsible for LCA, especially in the context of genetic counseling for individual patients in a clinical setting.

Molecular epidemiology of mtDNA mutations in 903 Chinese families suspected with Leber hereditary optic neuropathy

AbstractWe report the molecular epidemiology of three primary mutations in mitochondrial DNA (mtDNA) responsible for Leber hereditary optic neuropathy (LHON) based on analysis of probands suspected with LHON from 903 Chinese families. Most of them had optic neuropathy of unknown cause, and only 128 had a family history of optic neuropathy. Mutations in the mtDNA were detected in 346 probands. Of the 346 cases, 340 were homoplasmic and only six were heteroplasmic; 284 were male and 62 were female; 120 had a family history and 226 were sporadic. G11778A, T14484C and G3460A mutations were detected in 312 (90.2%), 30, and four families, respectively. The majority (226/346, 65.3%) of all LHON cases in Chinese are sporadic. These 226 probands (29.2%) were identified from 775 probands with sporadic optic neuropathy. Affected male-to-female ratio was 4.6:1 for all probands but was 2.2:1 for family members. Average age at onset was 18.5 years, ranging from 4.5 to 47 years old.

Strikingly different penetrance of LHON in two Chinese families with primary mutation G11778A is independent of mtDNA haplogroup background and secondary mutation G13708A

The penetrance of Lebers hereditary optic neuropathy (LHON) in families with primary mitochondrial DNA (mtDNA) mutations is very complex. Matrilineal and nuclear genetic background, as well as environmental factors, have been reported to be involved in different affected pedigrees. Here we describe two large Chinese families that show a striking difference in the penetrance of LHON, in which 53.3% and 15.0% of members were affected (P<0.02), respectively. Analysis of the complete mtDNA genome of the two families revealed the presence of the primary mutation G11778A and several other variants suggesting the same haplogroup status G2a. The family with higher penetrance contained a previously described secondary mutation G13708A, which presents a polymorphism in normal Chinese samples and does not affect in vivo mitochondrial oxidative metabolism as described in a previous study. Evolutionary analysis failed to indicate any putatively pathogenic mutation that cosegregated with G11778A in these two pedigrees. Our results suggest that the variable penetrance of LHON in the two Chinese families is independent of both their mtDNA haplotype background and a secondary mutation G13708A. As a result, it is likely that unknown nuclear gene involvement and/or other factors contribute to the strikingly different penetrance of LHON.

High Myopia Is Not Associated with the SNPs in the TGIF, Lumican, TGFB1, and HGF Genes

PURPOSE Four single-nucleotide polymorphisms (SNPs) in the TGIF, lumican, TGFB1, and HGF genes have been declared to be associated with high myopia in Chinese living in southeast China, but none of them has been confirmed by additional studies. This study was conducted to verify the reported positive association results by analysis of subjects from the same region. METHODS DNA was prepared from venous leukocytes of 288 patients with high myopia and 208 control subjects. The four SNPs (rs2229336, rs3759223, rs1982073, and rs3735520) in the four genes were genotyped by restriction fragment length polymorphism (RFLP) analysis. The allele and genotype frequencies of these SNPs from patients and control subjects were compared by chi(2) test. RESULTS Polymorphism at rs2229336 was not detected in all 496 subjects. There were no statistically significant differences between patients and control subjects for the other three SNPs: rs3759223, rs1982073, and rs3735520. CONCLUSIONS The study does not support the association of high myopia with alleles of rs2229336 in TGIF, rs3759223 in lumican, rs1982073 in TGFB1, and rs3735520 in HGF. These results provide a view contrary to those in previous reports. Reasonable criteria as well as replication should be the first priority for genetic association studies to avoid excessive expansion of false-positive results, especially for high myopia.

Protective effects of tetramethylpyrazine on rat retinal cell cultures

The retinal degeneration characterized with death of retinal ganglion cells is a pathological hallmark and the final common pathway of various optic neuropathies. Thus, there is an urgent need for identifying potential therapeutic compounds for retinal protection. Tetramethylpyrazine has been suggested to be neuroprotective for central neurons by acting as an antioxidant and a calcium antagonist. In this study, we tested the effects of tetramethylpyrazine on the viability of both neuronal and non-neuronal cells in mixed rat retinal cell cultures during a long-term cultivation or following hydrogen peroxide treatments. Cellular and biochemical analyses demonstrated that 50 microM tetramethylpyrazine significantly preserved neuronal morphology and survival in retinal cell cultures following 4-week in vitro cultivation as well as lethal exposures to hydrogen peroxide (10 microM or 50 microM for 24h). Hydrogen peroxide treatments induced remarkable increases in lipid peroxidation and mitochondrial reactive oxygen species (ROS) generation paralleled by the loss of mitochondrial membrane potential, microtubule-associated protein-2 (MAP-2) in neuronal soma and rattin peptide in cultured cells. Addition of tetramethylpyrazine in the cultures efficiently attenuated the signs of oxidative stress and retained abundance of MAP-2 and rattin in association with cell survival. In addition, siRNA-mediated downregulation of MAP-2 or rattin significantly increased the vulnerability of retinal neurons or the number of degenerating cells in the cultures, respectively, whereas exogenous humanin peptide, an analog of rattin, promoted cell survival in cultures under hydrogen peroxide attacks. These results suggest that tetramethylpyrazine protect retinal cells through multiple pathways and might be a potential therapeutic candidate for retinal protection in certain optic neuropathies.

The de-ubiquitinylating enzyme, USP2, is associated with the circadian clockwork and regulates its sensitivity to light.

We have identified a novel component of the circadian clock that regulates its sensitivity to light at the evening light to dark transition. USP2 (Ubiquitin Specific Protease 2), which de-ubiquitinylates and stabilizes target proteins, is rhythmically expressed in multiple tissues including the SCN. We have developed a knockout model of USP2 and found that exposure to low irradiance light at ZT12 increases phase delays of USP2−/− mice compared to wildtype. We additionally show that USP2b is in a complex with several clock components and regulates the stability and turnover of BMAL1, which in turn alters the expression of several CLOCK/BMAL1 controlled genes. Rhythmic expression of USP2 in the SCN and other tissues offers a new level of control of the clock machinery through de-ubiqutinylation and suggests a role for USP2 during circadian adaptation to environmental day length changes.

Novel SOX2 Mutation Associated With Ocular Coloboma in a Chinese Family

OBJECTIVES To report a novel SOX2 (OMIM 184429) mutation in a Chinese family and to describe its ocular and extraocular clinical features. METHODS Ocular and systemic examinations were performed, and genomic DNA was prepared from peripheral leukocytes. The coding exons and the adjacent intronic sequence of SOX2 were analyzed by cycle sequencing. RESULTS A novel heterozygous c.695C>A (p.Thr232Asn) mutation in SOX2 was identified in a Chinese family in which both the father and the son had iris and chorioretinal uveal colobomas. In addition, cataracts were noted in the father but not in the son. Other anomalies were not found in the father but were present in the son, including brain arachnoid cyst, microcornea, retrobulbar colobomatous orbital cyst, and penoscrotal hypospadias. This mutation was not detected in the unaffected mother and 103 unaffected control individuals. CONCLUSIONS Mutation in SOX2 is associated with typical ocular coloboma and probably other anomalies in this Chinese family. Arachnoid cyst has not been reported in individuals with the SOX2 mutation. CLINICAL RELEVANCE The results remind us that ocular coloboma may be accompanied by arachnoid cyst and may be associated with SOX2 mutation, which will be helpful for improving diagnosis and patient care.