Barkur S. Shastry

Mutant frizzled-4 disrupts retinal angiogenesis in familial exudative vitreoretinopathy

Familial exudative vitreoretinopathy (FEVR) is a hereditary ocular disorder characterized by a failure of peripheral retinal vascularization. Loci associated with FEVR map to 11q13–q23 (EVR1; OMIM 133780, ref. 1), Xp11.4 (EVR2; OMIM 305390, ref. 2) and 11p13–12 (EVR3; OMIM 605750, ref. 3). Here we have confirmed linkage to the 11q13–23 locus for autosomal dominant FEVR in one large multigenerational family and refined the disease locus to a genomic region spanning 1.55 Mb. Mutations in FZD4, encoding the putative Wnt receptor frizzled-4, segregated completely with affected individuals in the family and were detected in affected individuals from an additional unrelated family, but not in normal controls. FZD genes encode Wnt receptors, which are implicated in development and carcinogenesis. Injection of wildtype and mutated FZD4 into Xenopus laevis embryos revealed that wildtype, but not mutant, frizzled-4 activated calcium/calmodulin-dependent protein kinase II (CAMKII) and protein kinase C (PKC), components of the Wnt/Ca2+ signaling pathway. In one of the mutants, altered subcellular trafficking led to defective signaling. These findings support a function for frizzled-4 in retinal angiogenesis and establish the first association between a Wnt receptor and human disease.

SNPs: impact on gene function and phenotype.

Single nucleotide polymorphism (SNP) is the simplest form of DNA variation among individuals. These simple changes can be of transition or transversion type and they occur throughout the genome at a frequency of about one in 1,000 bp. They may be responsible for the diversity among individuals, genome evolution, the most common familial traits such as curly hair, interindividual differences in drug response, and complex and common diseases such as diabetes, obesity, hypertension, and psychiatric disorders. SNPs may change the encoded amino acids (nonsynonymous) or can be silent (synonymous) or simply occur in the noncoding regions. They may influence promoter activity (gene expression), messenger RNA (mRNA) conformation (stability), and subcellular localization of mRNAs and/or proteins and hence may produce disease. Therefore, identification of numerous variations in genes and analysis of their effects may lead to a better understanding of their impact on gene function and health of an individual. This improved knowledge may provide a starting point for the development of new, useful SNP markers for medical testing and a safer individualized medication to treat the most common devastating disorders. This will revolutionize the medical field in the future. To illustrate the effect of SNPs on gene function and phenotype, this minireview focuses on evidences revealing the impact of SNPs on the development and progression of three human eye disorders (Norrie disease, familial exudative vitreoretinopathy, and retinopathy of prematurity) that have overlapping clinical manifestations.

SNPs in disease gene mapping, medicinal drug development and evolution

AbstractSingle nucleotide polymorphism (SNP) technologies can be used to identify disease-causing genes in humans and to understand the inter-individual variation in drug response. These areas of research have major medical benefits. By establishing an association between the genetic make-up of an individual and drug response it may be possible to develop a genome-based diet and medicines that are more effective and safer for each individual. Additionally, SNPs can be used to understand the molecular mechanisms of sequence evolution. It has been found that throughout the given gene, the rate, type and site of nucleotide substitutions as well as the selection pressure on codons is not uniform. The residues that evolve under strong selective pressures are found to be significantly associated with human disease. Deleterious mutations that affect biological function of proteins are effectively being rejected by natural selection from the gene pool. If substituted nucleotides are fixed during evolution then they may have selection advantages, they may be neutral, or they may be deleterious and cause pathology. Therefore, it is possible that disease-associated SNPs (or pathology) and evolution can be related to one another.

Bipolar disorder: an update.

Bipolar disorder (BPD) is one of the most severe forms of mental illness and is characterized by swinging moods. It affects both sexes equally in all age groups and its worldwide prevalence is approximately 3-5%. The clinical course of illness can vary from a mild depression to a severe form of mania. The condition has a high rate of recurrence and if untreated, it has an approximately 15% risk of death by suicide. It is the third leading cause of death among people aged 15-24 years and is a burden on society and families. The pathophysiology of the disorder is poorly understood. However, a variety of imaging studies suggests the involvement of structural abnormalities in the amygdala, basal ganglia and prefrontal cortex. There are two main biological models that have been proposed for depression. These are called the serotonin and norepinephrine hypotheses. Multiple lines of evidence support both of them. It is a life-long disease and runs in families but has a complex mode of inheritance. Family, twin and adoption studies suggest genetic factors but the candidate susceptibility genes, which when mutated can account for a substantial portion of BPD patients, have not yet been conclusively identified. There have been an increasing number of new generation antidepressant drugs developed to treat BPD. However, lithium salt is only the drug that is most efficient in long-term preventive treatment and it also has an anti-suicidal effect. The condition can be well managed by physicians and psychiatrists along with family and patient education. Identification of risk genes in the future may provide a better understanding of the nature of pathogenesis that may lead to a better therapeutic target.

Genetic diversity and new therapeutic concepts.

AbstractThe differences in medicinal drug responses among individuals had been known for quite some time. Some patients exhibit a life-threatening adverse reaction while others fail to show an expected therapeutic effect. Intermediate responses between the above two extreme cases are also known. In fact, it has been recently reported that approximately 100,000 deaths and more than 2 million hospitalizations annually in the United States are due to properly prescribed medications. This interindividual variability could be due in part to genetically determined characteristics of target genes or drug metabolizing enzymes. This has now been substantiated by a variety of studies. We know that “one size fits all” is not correct. Therefore, the application of pharmacogenetic concepts to clinical practice is an excellent goal in the postgenomic era. The successful completion of the human genome project provided necessary molecular tools, such as high-throughput SNP genotyping, HapMap, and microarray, that can be applied to develop proper therapeutic options for individuals. Recently, there have been considerable scientific, corporate, and policy interest in pharmacotherapy. However, identification of causal variations in a target gene is only a starting point, and the progress in this rapidly developing field is slower than expected. One major drawback could be due to the multigene determinant of drug response that requires a genome-wide screening. Additionally, application of pharmacogenetic knowledge into clinical practice requires a high level of accuracy, precision (risk/benefit ratio), and strict regulations. This is because the pharmacogenetic approach raises several ethical, moral, and legal questions. It is also necessary that both health professionals and the general public must be urgently educated. Despite these limitations, translation of pharmacogenomic data into clinical practice would certainly provide better opportunities to increase the safety and efficacy of medicine in the future.

Developmental dyslexia: an update

AbstractDyslexia is the most common and carefully studied of the learning disabilities in school-age children. It is characterized by a marked impairment in the development of reading skills, and affects a large number of people (5-10%). Reading difficulties may also arise from poor vision, emotional problems, decreased hearing ability, and behavioral disorders, such as attention-deficit hyperactivity (ADHD). Although many areas of the brain are involved in reading, analysis of postmortem brain specimens by a variety of imaging techniques most consistently suggests that deficiency within a specific component of the language system—the phonologic module—in the temporo-parietal-occipital brain region underlies dyslexia. It is a highly familial and heritable disorder with susceptibility loci on chromosomes 1, 2, 3, 6, 11, 13, 15 and 18. Recently, four candidate genes (KIAA 0319, DYX1C1, DCDC2 and ROBO1) are shown to be associated with dyslexia. Although some of these results are controversial because of the genetic heterogeneity of the disorder, the available evidence suggests that dyslexia could be due to the abnormal migration and maturation of neurons during early development. Interestingly, in spite of genetic heterogeneity, the pathology appears to involve common phonological coding deficits. The condition can be managed by a highly structured educational training exercise.

Lack of association of the VEGF gene promoter (−634 G→C and −460 C→T) polymorphism and the risk of advanced retinopathy of prematurity

BackgroundRecently, it has been reported that genetic polymorphism (−634 G→C and −460 C→T) in the promoter region of the vascular endothelial growth factor (VEGF) gene can influence the progression of retinopathy of prematurity (ROP). In order to evaluate its general applicability as a screening procedure in clinics and to replicate the above result, we have undertaken the following study.MethodsWe have analyzed a cohort of 61 patients with advanced ROP (stage 4 and 5) along with 61 normal controls for the VEGF gene promoter polymorphism. For this purpose, blood samples were collected from each patient and leukocyte DNA was isolated. Genomic DNA was amplified by the polymerase chain reaction (PCR) method with two pairs of primers designed to amplify separately the promoter region (containing −634 G→C and −460 C→T polymorphism) of the VEGF gene. The amplified product was subjected to restriction enzyme digestion. The base change in the restriction site was further confirmed by a BigDye terminator cycle sequencing of the amplified product.ResultsOur analysis suggests that there is no significant difference in allelic frequency of the VEGF gene between normal subjects and patients with advanced ROP in our cohort.ConclusionOur results do not support the association of the VEGF gene promoter polymorphism and the risk of advanced ROP. In order to adapt this method for the identification of high-risk infants in clinics in the future, a large-scale study involving a mixed ethnically diverse population is much needed.

Molecular genetics of autism spectrum disorders

AbstractAutistic disorder belongs to a broad spectrum of pervasive developmental disorders. Autism is a clinically and genetically heterogeneous condition. It is characterized by impairment in a broad range of social interactions, communication, and repetitive patterns of behavior and interest. Although the exact etiology of the condition is not known, family and twin studies strongly support genetic factors in autism. Genome-wide scans suggest several susceptibility loci that may contain one or more predisposing genes. However, no such genes have been identified so far that predispose patients to autism. The condition is over 90% heritable, but the mode of inheritance is not clear. Moreover, it does not seem to be a single gene disorder. There is no cure for autism. Individualized structured education, family support services, and antipsychotic drugs are recommended. These may alleviate some behavioral problems. The identification of autism genes, an understanding of the neurobiology of the condition, and additional clinical studies may help to develop pharmacological interventions in the future.

Genetic diversity and medicinal drug response in eye care

BackgroundIndividual variation in drug response and adverse drug reactions are a serious problem in medicine. This inter-individual variation in drug response could be due to multiple factors such as disease determinants, environmental and genetic factors. Much has been published in the literature in recent years about the potential of pharmacogenetic testing and individualized medicine. The development of personalized medicine is truly an exciting area of research.MethodsThis pharmacogenetic concept in ophthalmology has existed for more than a century. Although substantial studies that link genetic variants to inter-individual difference in drug response have been reported in several diseases such as cancer and heart diseases, such studies are progressing slowly in the eye field. In this short article, an attempt has been made to summarize these results.ResultsRecently, there have been some small-scale studies that seem to associate the drug response to the genotype of patients in two major eye disorders, namely age-related macular degeneration (ARMD) and glaucoma.ConclusionThese studies are still in their infancy, and do not suggest that a pharmacogenetic basis of drug development is a credible concept and can become reality in the future. This is because most drug responses involve a large number of genes that have several polymorphisms and it is unlikely that any one single gene dictates the drug response. Therefore, a polygenic approach, whole genome single nucleotide polymorphism (SNP) analysis and a molecular understanding of disease itself may provide a better insight in the future about genetic predisposing factors for adverse drug reactions.

Assessment of the contribution of the LOC387715 gene polymorphism in a family with exudative age-related macular degeneration and heterozygous CFH variant (Y402H).

AbstractAge-related macular degeneration (AMD) is a common cause of visual impairment in the elderly population in developed countries. The etiology of AMD is not completely understood but environmental and genetic factors have been implicated in the disease. Recently it has been documented that variations in the complement factor H (CFH) and LOC 387715 genes are the major risk factors that predispose individuals to dry and wet AMD. To investigate further the genetic contribution to AMD, we have analyzed the LOC 387715 gene in a non-smoking family with an exudative AMD and a heterozygous mutation (Y402H) in the CFH gene. Direct sequencing of the amplified product of exon 1 of the LOC 387715 gene identified a previously reported missense mutation (A69S) in this family. The affected individual is homozygous for the mutation and this sequence alteration was not identified in six age-matched controls. On the basis of this and other results it is tempting to speculate that the combined effect of variants in the CFH and LOC 387715 genes may contribute to the AMD phenotype in this family. Further studies on these and other susceptibility genes may provide clues on variable phenotypes, new preventive strategies and treatment options for AMD.