Srinivasan Muthuswamy

Imbalanced oxidant and antioxidant ratio in myotonic dystrophy type 1

Abstract Myotonic dystrophy type 1 (DM1) is the most common form of muscular dystrophy affecting adults and is due to trinucleotide sequence (CTG) in the 3′ UTR region of DMPK gene located at 19q13.3 chromosome. The pathogenic mechanisms of multisystemic involvement of DM1 are still unclear. The increased levels of reactive oxygen species/free radicals and lipid peroxides and decreased antioxidant levels play an important role in the pathogenesis of DM1. Present study includes 20 DM1 patients and 40 age- and sex-matched controls. Malonilaldehyde (MDA), superoxide dismutase (SOD), glutathione peroxidise (GPX), glutathione-S-transferase (GST), reduced glutathione (GSH), and TAS levels were measured and its association with clinical phenotype were evaluated. Results revealed significantly higher levels of MDA (p = 0.002), SOD (p = 0.006), and TAS p = 0.004) and lower level of GPX (p = 0.003), GST (P < 0.001) and GSH (P = 0.016) in DM1 patients. A significant negative correlation of MDA level with dyspepsia and CK-MB and GST level with serum SCK, CK-MB, and diabetes were observed. However, a significant positive correlation of SOD level with serum CK-MB, CK-MM, and diabetes and negative correlation with facial weakness were noted. Though, GSH level had significant positive correlation with learning and writing disability, speech, and languages disability yet found negative correlation with duration of disease. The GPX and TAS showed no correlation with any clinical findings. Our data further support the pathogenic role of oxidative stress in DM1 of Indian origin and support the opportunity to undertake clinical trials with antioxidants in this disorder.

Association of CFTR gene mutation with bronchial asthma and its severity in Indian children: a case-control study.

Background: Asthma is a complex genetic disorder. Several genes have been found associated with asthma. The cystic fibrosis transmembrane conductance regulator (CFTR) gene is one of them. Aim: To assess the association of CFTR gene mutation with asthma and its severity as per GINA guidelines. Subjects and methods: This was a hospital-based case-control study. Excluded from cases and controls were those with clinically suspected cystic fibrosis or sweat chloride level>60 mmol/L or suffering from other respiratory diseases. Included were 200 cases and 180 controls, aged 5 months to 15 years. Screening was done for CFTR gene mutations; ΔF508, G542X, G551D, R117H and W1282X using the ARMS-PCR method. Results: ΔF508 was found in three (1.5%) cases and two (1.1%) controls (p = 0.739), G542X in nine (4.5%) cases and five (2.8%) controls (p = 0.374), R117H in one (0.5%) case and one (0.6%) control (p = 0.940) and G551D in twelve (6.0%) cases and two (1.1%) controls (p = 0.012). Individuals carrier for G551D mutation had increased risk for persistent asthma (p = 0.006). Percent predicted FEV1 (p = 0.014) and FVC (p = 0.028) were significantly lower among carriers as compared to non-carriers. Conclusion: Significantly higher frequency of G551D mutation among asthma patients compared with controls suggests that this mutation may increase risk for the disease and also its severity.

Friedreich Ataxia: From the Eye of a Molecular Biologist.

Friedreich ataxia (FRDA) is caused by the expansion of a GAA triplet repeat in the first intron of the FXN gene. This disease was named after Nicholaus Friedreich, Germany, who depicted the essential finding. Among ataxias, FRDA is the most common hereditary ataxia. It has the autosomal recessive pattern of inheritance. The expansion of the GAA triplet repeat hinders the transcription, thereby reducing the level of the FXN transcript and consequently reducing the level of frataxin, a 210-amino acid protein. The disease pathogenesis is fundamentally due to a lack of frataxin, which is claimed to play a role in iron-sulfur cluster synthesis. Oxidative stress builds up as a result of Fe accumulation in the mitochondria, causing degeneration of the cells, which primarily occurs in the neurons and later in the cardiac tissues, and to some extent in the pancreas. The therapeutic interventions are at infancy; however, current treatments are targeted toward the reduction of iron overload and its effects.

Spectrum and distribution of CFTR gene mutations in asthma and chronic pancreatitis cases of North Indian population.

BACKGROUND Cystic fibrosis transmembrane conductance regulator (CFTR) gene accounts for an autosomal recessive condition called cystic fibrosis (CF). In the Indian subcontinent, CF and its related diseases are under-diagnosed by the medical community due to poor knowledge of the disease and its confounding diagnosis, and also due to poor medical facilities available for these patients, thus causing an increased infant mortality rate with a low life expectancy in general. The aim of the study was to document the spectrum and distribution of CFTR mutations in controls, asthma and chronic pancreatitis cases of North India. METHODS A total of 800 subjects including 400 controls, 250 asthma cases and150 chronic pancreatitis cases were analyzed for 6 mutations (F508del, G542X, G551D, R117H, W1282X, and S549N) and IVS8 Tn polymorphism. RESULTS Out of 800 subjects, 18% [asthma - 24% (n=250), CP - 29.33% (n=150) cases and controls - 9.3% (n=400)] were positive for heterozygous mutation, 0.8% of the (n=250) asthmatic cases (n=250) were homozygous for IVS8 T5 polymorphism while no subjects were found positive for W1282X mutation. T5 polymorphism was more common in asthmatic cases while F508del mutation in chronic pancreatitis cases. The carrier frequency of F508del, G542X, G551D, R117H, S549N and T5 was 0.015, 0.025, 0.02, 0.005, 0.005, and 0.022 respectively. The cumulative carrier frequency was 0.093. CONCLUSION CFTR mutations were underestimated in Indian population. The present study will serve in establishment of genetic screening and prenatal setup for Indian population.

Performance of QF-PCR in targeted prenatal aneuploidy diagnosis: Indian scenario.

OBJECTIVE Among the rapid aneuploidy detection methods, QF-PCR has now become an alternative tool for prenatal aneuploidy diagnosis concomitant with karyotyping. This method has been validated in many of the western clinics but in India no study was conducted to assess its utility as standalone procedure. The study was designed to answer the question whether QF-PCR can be implemented as a standalone diagnostic method for rapid aneuploidy diagnosis in our present clinical setup? MATERIALS AND METHODS Study was conducted during March 2012 to August 2014 consisting of 270 prenatal samples that underwent for aneuploidy diagnosis. In addition to karyotyping, QF-PCR was also performed on these samples and the results were compared. RESULTS Of 270 samples screened, 262 samples showed euploid genome (125 normal male and 137 normal female). Eight samples were consistent with aneuploidy--four trisomy 21 male sample, 2 trisomy 21 female sample, 1 trisomy 18 samples and 1 Klinefelter sample. The specificity, sensitivity, positive prediction value and negative prediction values were 100% while false positive rate and false negative rate were 0%. CONCLUSION Outcome of this study strongly suggests that QF-PCR can be used as standalone procedure for targeted rapid aneuploidy diagnosis.

CRELD1 gene variants and atrioventricular septal defects in Down syndrome

Congenital heart defects (CHD) are seen in around 40% of the Down syndrome patients. Atrioventricular Septal Defect (AVSD) or endocardial cushion defect is commonest form of CHD in these children. CRELD1 gene is implicated in causation of sporadic AVSD. In the present study, we evaluated the association and significance of CRELD1 variants with AVSD in Down syndrome (DS) patients. Sequencing was done in blood samples from 3 groups: group I (DS with AVSD), group II (DS without AVSD) and group III (non-syndromic AVSD cases). Twenty two variants in CRELD1 gene were identified, comprising of sixteen novel and six previously reported variants. However, on the basis of sequence, as well as structure analysis, the variant c.973G>A(p.Glu325Lys) variant was identified only in DS having AVSD group which was predicted to have significant effects on calcium binding of putative CRELD1 protein. Since CRELD1 gene acts as a regulator of calcineurin/NFATc1 signaling which is crucial for the regulation of cardiac development by dephosphorylation of the transcription factor, NFAT(nuclear factor of activated T cells),in cytoplasm, the variation in cb-EGF-like calcium binding domain in CRELD1 protein is likely to have pathogenic consequences. Thus, we conclude that the CRELD1 gene is likely to have a major role in causation of AVSD phenotype in selected DS patients.

Co-existence of CFTR and SPINK1 Gene Mutations in an Idiopathic Chronic Pancreatitis Case

Familial aggregation of CP suggests genetic factors for disease without definitive mode of inheritance. The hypothesized primary putative gene for CP includes SPINK1, CTSB, CTRC, PRSS1 and CFTR. These genes interact with each other and exhibit a variable phenotype in patients. The present report describes a male adult aged 42 years with a complaint of severe recurrent pain in the abdomen and weight loss and the age of onset was 35 years. The family history of chronic pancreatitis was not found. The biochemical examination revealed the exocrine insufficiency. Abdominal CT identified a dilated main pancreatic duct with numerous stones in the pancreas head. Genetic studies identified the patient to be heterozygous for p.N34S and G551D in SPINK1 and CFTR gene. Extended family screening identified his son (10 years) to have the both mutation p.N34S and G551D mutation in heterozygous state. Present findings suggest the need of genetic diagnosis in familial CP cases thereby precaution can be taken to delay or avoid the disease onset.

Young mothers and higher incidence of maternal meiosis-I non- disjunction: Interplay of environmental exposure and genetic alterations during halt phase in trisomy 21

Trisomy 21 is a genetic condition caused when chromosomes fail to separate during meiosis. We have studied conventional karyotype and QF-PCR using STR markers with high polymorphism and heterogeneity and the results were analyzed, to determine the paternal and meiotic origin of trisomy 21. This study was conducted using a detailed questionnaire to include: paternal, maternal, clinical and family history for various confounding factors such as age and regional environmental exposures where the parents resided. Out of 120 samples 95% (N = 114) were of maternal origin, including 92% (N = 105) of meiosis 1 errors and 8% (N = 9) meiosis 2 errors. Paternal origin accounted for 5% (N = 6) and were all due to meiosis-I errors. The higher incidence of maternal meiosis-I observed in the present study suggests that human trisomy 21 non-disjunction is a result of multiple factors contributing to the origin of the genetic condition.

Current molecular insight to reveal the dynamics of CAG repeating units in spinocerebellar ataxia

Spinocerebellar ataxia (SCA) is a heterogeneous genetic disorder with overlapping clinical phenotypes arising from the degeneration of purkinje cells and other regions of the brain. There are approximately 36 different subtypes of SCA, but SCA 1, 2, 3, 6 and 7 are most prevalent in the Indian population. Many findings suggested that cerebellar Purkinje cells region may be a uniquely vulnerable neuronal cell type, and more susceptible to a wider variety of genetic or cellular problems than other neuron types. In this review we emphasized mainly five common subtypes of SCA (1, 2, 3, 6 and 7) their pathophysiology, therapeutics, drugs studies and the technical challenges in the field of molecular genetic diagnosis.

Segmental Duplication QF-PCR: A Simple and Alternative Method of Rapid Aneuploidy Testing for Developing Country Like India

Aneuploidy screening is becoming an integral part of routine prenatal screening in developing countries like India, and the need for more cheaper and rapid aneuploidy testing methods are required to relive the anxiety and financial burden among the high‐risk couples. Segmental duplication quantitative fluorescent polymerase chain reaction (SD‐QF‐PCR) emerged as an alternative aneuploidy diagnostic method.