CYP2C9, VKORC1, CYP4F2, ABCB1 and F5 variants: influence on quality of long-term anticoagulation.

AIMS: The study aims to evaluate the impact of genetic, demographic and clinical data on various measures of outcome of anticoagulation quality in patients. PATIENTS AND METHODS: The study consisted of 310 patients receiving long-term oral anticoagulation therapy in our hospital. Apart from demographic and clinical variables, 21 SNPs (in 7 genes) were analyzed and compared with the outcomes of anticoagulation therapy. Various outcomes that were measured are; supra therapeutic INRs (INR >3, >6), anticoagulation stabilization, time taken to stabilize and proportion of INRs within (2-3), above (>3) and below (<2) therapeutic range. RESULTS: Supra therapeutic INRs were influenced by CYP2C9*2, *3, CYP4F2 rs2108622, VKORC1-1639G>A, 1173C>T, rs55894764 along with concomitant drugs, smoking, body weight and height. Persistently fluctuating INRs/absolute instability correlated with VKORC1-1639G>A, gender, height and body mass index. The time taken to stabilize was associated with CYP4F2 rs2108622, CYP2C9*14, smoking, clinical indication and concomitant drugs. The overall distribution of INR was influenced by variants in CYP4F2 rs2108622, CYP2C9*3, rs9332230, VKORC1 1173C>T, -1639G>A, rs55894764, ABCB1 rs2032582, rs1128503, rs1045642 and F5 rs6025, age, smoking and concomitant drugs. CONCLUSIONS: Knowledge of factors influencing the quality of long term anticoagulation can help clinicians to customize therapy either by dose variation, therapy with alternate choice of drug, concurrent heparin therapy and/or frequent INR monitoring.

Variability in CYP2C9 allele frequency: a pilot study of its predicted impact on warfarin response among healthy South and North Indians.

BACKGROUND: Wide variability exists in the frequency of pharmacogeneticmarkers for anticoagulant response in different populations. There is insufficient data on the prevalence of these variant genotypes in the Indian population. This study aims to determine the frequency of various genotype combinations of CYP2C9*2, *3 and VKORC1-1639G>A polymorphisms in the South and North Indians. METHODS: Genotyping was carried out by PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism) technique in 209 North Indians (NI) and 82 South Indians (SI). Warfarin maintenance dose was predicted for all subjects based on FDA approved genotype-based dose estimates from revised COUMADIN medication guide. Fisher exact test and Χ2 test were applied to compare categorical data among the SI and NI groups. RESULTS: In SI and NI, the allele frequency of CYP2C9*2 was 0.006 and 0.05 (significant variation; p<0.001); of CYP2C9*3 was 0.09 and 0.11; and of VKORC1-1639A was 0.14 and 0.19 (not significant), respectively. The variation in the frequency of combined CYP2C9/ VKORC1 genotypes revealed plausible difference in warfarin response among SI and NI. Based on the FDA approved revised dosing guidelines, significantly higher percentage of NI were likely to require intermediate dose (3-4 mg/day; p=0.015, RR=2.16) and were also predicted to have an increased risk of bleeding episodes and over anticoagulation (p=0.012, RR=1.93). CONCLUSIONS: Genotype frequency of CYP2C9 and VKORC1 SNPs is variable among the two ethno-geographically distinct Indian populations. This could translate into diverse warfarin response among the Indian population.

Implication of novel CYP2C9*57 (p.Asn204His) variant in coumarin hypersensitivity.

INTRODUCTION: Polymorphisms in CYP2C9 can vary the rate of metabolic clearance of oral anticoagulants, risking toxicity in patients. The present study focused on exploring the genetic etiology of idiopathic hyper sensitivity to coumarin anticoagulants in a patient who presented with multiple bleeding episodes and supra-elevated International Normalized Ratios. MATERIALS AND METHODS: Bidirectional gene sequencing of CYP2C9 and VKORC1 was carried out. Using allele-specific polymerase chain reaction, the identified novel variant was genotyped in 309 patients on anticoagulation therapy. The pharmacoproteomic significance of the novel genetic variant was elucidated by structural demonstration of binding of coumarin molecules within the mutant CYP2C9 204His protein model and in silico bioinformatic evolutionary analyses. Three-dimensional structure model of the mutant protein was constructed on the basis of the published X-ray crystal structure of human CYP2C9 protein (Protein Data Bank, 1R9O). RESULTS: The patient was identified to have a novel heterozygous missense mutation in exon 4 of CYP2C9 gene (g.9172A > C; p.Asn204His; CYP2C9*57). The variant was absent in the 309 genotyped patients. In silico bioinformatic analyses indicated the variant to have a deleterious effect on the protein. Analysis of 3D structure model of the mutant protein revealed that the substituted His204 led to restricted binding of the coumarin drug within the binding site of CYP2C9 enzyme, thereby inhibiting its metabolic clearance and thus explaining the enhanced pharmacologic effect and bleeding in the patient. CONCLUSIONS: The study elucidates the structurally deleterious role of the novel CYP2C9*57 missense mutation in coumarin toxicity.

Do parental perceptions and motivations towards genetic testing and prenatal diagnosis for deafness vary in different cultures?

Surveys of attitudes of individuals with deafness and their families towards genetic testing or prenatal diagnosis have mostly been carried out in the West. It is expected that the perceptions and attitudes would vary amongst persons of different cultures and economic background. There is little information on the prevailing attitudes for genetic testing and prenatal diagnosis for deafness in developing countries. Therefore, this study evaluates the motivations of Indian people with inherited hearing loss towards such testing. Twenty-eight families with history of congenital hearing loss (23 hearing parents with child/family member with deafness, 4 couples with both partners having deafness and 1 parent and child with deafness) participated in a semi-structured survey investigating their interest, attitudes, and intentions for using genetic and prenatal testing for deafness. Participants opinioned that proper management and care of individuals with deafness were handicapped by limited rehabilitation facilities with significant financial and social burden. Nineteen (68%) opted for genetic testing. Twenty-six (93%) expressed high interest in prenatal diagnosis, while 19 (73%) would consider termination of an affected fetus. Three hearing couples, in whom the causative mutations were identified, opted for prenatal diagnosis. On testing, all the three fetuses were affected and the hearing parents elected to terminate the pregnancies. This study provides an insight into the contrasting perceptions towards hearing disability in India and its influence on the desirability of genetic testing and prenatal diagnosis.

Survival analysis of Down syndrome cohort in a tertiary health care center in India.

OBJECTIVE: To identify the major causes of death in Down Syndrome (DS), the ages at which mortality rates are the highest and recognize factors associated with it. METHODS: The prospective cohort-based study was carried out in a tertiary health care center. Children with DS (n = 543) counseled at the Center of Medical Genetics, Sir Ganga Ram Hospital from 2005 through 2009 were followed up in year 2010. Survival curves and Cox's proportional hazards regression analysis were used to determine the effect of different variables on survival. RESULTS: Total mortality was 13 %, of which 80.3 % was in children less than 2 y of age. Presence of congenital heart disease (CHD) increased the risk of mortality by 5.7 folds (p = 0.001). A definitive survival benefit after cardiac intervention was noted, although it differed with the type of CHD. Sex, maternal age at time of birth and karyotypes did not show a significant correlation with survival. CONCLUSIONS: The higher DS infant mortality observed in the present study could be attributed to financial constraints of the families and misconceptions amongst health professionals. It is recommended that a nation-wide DS registry be created to study the morbidity and mortality in Down syndrome from birth. The findings of this study will help clinicians in making management decisions and enable better counseling.

Pharmacogenetic typing for oral anti-coagulant response among factor V Leiden mutation carriers.

CONTEXT: Factor V Leiden mutation is the most common inherited predisposition for hypercoagulability and thereby a common genetic cause for initiation of oral anti-coagulation therapy. There is a dearth of knowledge of coumarin response profile in such thrombophilic population. AIMS: The current pilot study aims to estimate coumarin sensitivity in an Indian cohort with an inherited thrombophilia risk factor (Factor V Leiden mutation carriers) based on the observed frequency of CYP2C9 (*)2, (*)3 and VKORC1-1639G >A genotype combinations. SETTINGS AND DESIGN: A retrospective study carried out in a tertiary health care center in India. MATERIALS AND METHODS: Carriers of FVL mutation were genotyped for CYP2C9 ((*)2, F(*)3) and VKORC1 (-1639G >A) variants by PCR-RFLP technique. STATISTICAL ANALYSIS USED: Chi-square test to analyze difference in expected and observed genotype frequency. RESULTS: Sixty-one (n = 61) unrelated carriers of FVL mutation were observed in the 13 years study period. The allele frequency of CYP2C9 (*)2, CYP2C9 (*)3, and VKORC1-1639A in this cohort was 0.06, 0.11, and 0.16, respectively. Six (9.7%) individuals had two of the three variant alleles (heterozygous or homozygous), and 28 (45.9%) were heterozygous for at least one polymorphism. CONCLUSIONS: Pre-prescription genotyping for coumarin drugs, if introduced in Indians with inherited thrombophilia (in whom oral anti-coagulant therapy may be necessary), is likely to identify 9.7% (hypersensitive) subjects in whom the optimum anti-coagulation may be achieved with reduced dosages, 44.3% (normal sensitivity) who may require higher dose and also 55.6% (hyper and moderate sensitivity) subjects who are likely to experience bleeding episodes.

Molecular studies of achondroplasia.

BACKGROUND: Achondroplasia (ACH) is the most frequent form of short-limbed dwarfism, caused by mutations in the FGFR3 gene. It follows an autosomal dominant inheritance, though most cases are sporadic. The molecular techniques are the only available methods to confirm the diagnosis of a skeletal dysplasia. Clinical and radiological features are only suggestive and not confirmatory. The present study was conducted to find out how often the clinical diagnosis of achondroplasia is verified on molecular studies. MATERIALS AND METHODS: From 1998 through 2007, we carried out molecular analysis for the two common mutations in the FGFR3 gene in 130 cases clinically suspected to have ACH. RESULTS: A diagnostic mutation was identified in 53 (40.8%) cases. The common mutation (1138G>A) was present in 50 (94.7%) of the positive cases, while the rare 1138 G>C substitution was found in three (5.3%). CONCLUSION: This study shows that confirmation of clinical diagnosis of ACH by molecular genetic testing is essential to distinguish it from other skeletal dysplasias, to plan therapeutic options, and to offer genetic counseling. Management (medical and surgical) in patients confirmed to have ACH, is briefly discussed.