ABSTRACT



ABSTRACT

Purpose: To assess WDR36 gene (exon 18) polymorphisms are associated with primary open angle glaucoma (POAG) in the South Indian population.

Methods: 20 with POAG, including normal tension glaucoma and high tension glaucoma and 10 control subjects without glaucoma were analyzed for one WDR36 polymorphisms (V714V; a G→C substitution in exon 18) using allele specific primer PCR and RFLP respectively.

Results: No significant difference was observed regarding the WDR36 genotype frequencies at exon 18 between the NTG or HTG patients and the control subjects. In addition, there was no significant difference in the WDR36 allele frequencies at exon 18 between the NTG or HTG patients and the control subjects. V714V mutation in exon 18 was not found in this study.

Conclusion: WDR36 exon 18 polymorphism is a genetic risk factor for POAG however WDR36 exon 18 polymorphisms were not detected in POAG patients in the South Indian population. It has been concluded that the WDR36 polymorphism occurs very rarely in South Indian glaucoma patients. The other genes would have played crucial role in the development of POAG in South India.

INTRODUCTION

Glaucoma refers to a group of clinically and genetically heterogeneous ophthalmologic disorders leading to visual impairment and blindness. The characteristic clinical sign is cupping of the optic nerve head with subsequent retinal nerve fibers loss, usually associated with elevated intraocular pressure. The disease affects more than 67 million people worldwide (Quigley, 1996).

Epidemiologic studies have repeatedly confirmed that primary open-angle glaucoma (POAG), the most common adult form of the disease, is one of the main causes of blindness (8%) in European populations. (Klaver et al., 1998 and Tuck et al., 2003).

The age of onset of glaucoma manifestation ranges from birth to late adulthood. Affected individuals are usually asymptomatic until the late stages of disease, when significant and irreversible optic nerve degeneration has already occurred.(Fechtner et al., 1994) As glaucoma-related visual loss is preventable in many cases and as the sensitivity of current diagnostic methods is suboptimal, there is an urgent need to diagnose glaucoma in its early stages.(Viswanathan et al.,1999 and Ritch, 2000) Identification of the genes involved in the etiology of glaucoma provides a significant opportunity for presymptomatic diagnosis, improved prognosis, and better understanding of the etiology of this blinding condition.

Although many cases are sporadic, POAG shows familial clustering consistent with autosomal dominant inheritance and incomplete penetrance. Reduced penetrance and excess of sporadic cases is particularly seen in late-onset forms. Nevertheless, more than 11 (GLC1A-GLC1M) different POAG loci have been mapped so far.(Sarfarazi et al 1998, Stoilova et al.,1996, Trifan OC et al., 1998, Wirtz et al.,1999, Wiggs et al.,2000 and 2004).

During the past decade, two genes have been reported for POAG: myocilin (MYOC) on chromosome 1, long-arm region q24.3-q25.2, primarily mutated in juvenile-onset patients,(Stone et al .,1997) and optineurin (OPTN) on chromosome 10, short-arm region p14-p15, mainly mutated in individuals with normal-tension glaucoma (NTG).(Rezaie et al., 2002 and Sarfarazi et al., 2003) Although investigators in several studies have consistently found mutations in MYOC in approximately 3% of cases including the German population (3.2%),(Michels-Rautenstrauss et al.,2002) mutations in OPTN seem to be a rather infrequent cause of POAG or NTG.(Weisschuh et al., 2005 and Wiggs et al.,2003) In a recent study, a new POAG locus was identified on chromosome 5, region q22.1 (designated as GLC1G). Screening of the WD40-repeat 36 gene (WDR36) in 130 patients with an adult-onset form of glaucoma with high and low pressure identified mutations in approximately 5% of patients. Both familial and sporadic cases were affected. (Monemi et al., 2005)

WD40-repeats are stretches of 40 amino acids that contain tryptophan (W) and aspartic acid (D). WD-repeat–containing proteins comprise a large family found in all eukaryotes and are implicated in a variety of functions ranging from signal transduction and transcription regulation to cell cycle control and apoptosis. The underlying common function of all WD-repeat proteins is coordinating multiprotein complex assemblies, where the repeating units serve as a rigid scaffold for protein interactions. Based on sequence similarity, WDR36 was proposed to contain five (Mao M et al., 2004) to eight (Monemi et al., 2005) WD40 repeats. In addition, WDR36 contains a C-terminal UTP21 domain that is specifically associated with WD40 repeats (Bateman et al., 2002) as well as sequence stretches that are characteristic for AMP-binding or which exhibit structural similarity to the C-terminal part of cytochrome cd119.

Expression of WDR36 was shown in human ocular and nonocular tissues as well as in embryonic and adult mouse tissues.(Monemi et al., 2005) It has been suggested that WDR36 may be involved in T-cell activation (Mao et al., 2004) and recently, T-cell-mediated responses have been hypothesized to participate in glaucoma-associated optic nerve degeneration.(Bakalash et al., 2005) However, the exact physiological function of the protein and its role in glaucoma pathogenesis remain unclear.

The purpose of this study was to determine the prevalence of WDR36 V714V sequence variants in a well-characterized group of 20 unrelated South Indian patients with POAG, NTG, or juvenile open-angle glaucoma (JOAG).

REVIEW OF LITERATURE

Glaucomas are a group of optic neuropathies that, if untreated, can result in total blindness. The condition is classified according to the etiology (primary versus secondary), anatomy of the anterior chamber (open angle versus closed angle) and time of onset (infantile versus juvenile versus adult) (Shields et al., 1996). However, a more precise classification of this condition may only be possible when all the etiological factors, including primary defective molecules and other contributing risk factors, are identified.

Different forms of glaucoma share some common clinical manifestations that usually include specific abnormal appearance of the optic nerve head, characteristic loss of the visual field and chronic painless progression. Furthermore, the condition frequently is associated with increased intraocular pressure (IOP), but this elevation is neither necessary nor sufficient for onset or progression of the disease (Shields et al., 1996).

The manifestation of this group of eye conditions could start at birth or may appear after the age of 80, depending on the type of glaucoma present in an individual. The pediatric form of glaucoma (Buphthalmos) usually occurs at birth and up to the age of three, while juvenile-onset glaucoma may appear somewhere between the ages of 3 and 30 (Johnson et al., 1993). The late-onset form of this condition rarely starts before the age of 40 and is the most prevalent type observed in an everyday glaucoma clinic (Quigley, 1996). The pediatric and juvenile types of glaucoma are generally rare conditions and, while the incidence of the primary congenital type varies between 1 in 1250 (Gencik, 1989). and 1 in 10 000 (Francois, 1972) , no comparable estimates are available for the juvenile-onset type of glaucoma.

Although a large number of affected subjects have no previous family history (Quigley et al., 1997), a significant proportion show a clear familial aggregation with multiply affected subjects in their respective pedigrees (Raymond, 1997). Whereas the main mode of inheritance for primary congenital glaucoma is autosomal recessive (Sarfarazi. et al., 1995), for juvenile and adult-onset glaucoma the more frequently reported mode of inheritance is autosomal dominant with reduced penetrance (Bennett et al., 1989). A significant proportion of other ocular conditions associated with glaucoma are also inherited as autosomal dominant traits (Anderson et al., 1997).

In this article, the molecular genetics of different types of glaucoma will be reviewed in order to provide some insight into the molecular etiology of two well studied types of glaucoma, namely, the juvenile-onset primary open angle glaucoma and the pediatric form of primary congenital glaucoma. A brief summary on the current status of other types of ocular conditions associated with glaucoma will also be presented.

PRIMARY OPEN ANGLE GLAUCOMA (POAG)

This is the most common form of this group of eye conditions, usually accompanied with variable severity and phenotypic expressivity (Shields, et al., 1996). The clinical manifestation is further complicated with IOP measurements that could vary from 10 to >50 mm Hg. POAG have been arbitrarily divided into two groups of juvenile and adult with an overlapping clinical presentation and a sliding scale age of onset and IOP values (Shields et al., 1996). Although there are some differences between the rare form of juvenile-onset open angle glaucoma (JOAG) as compared with the more frequent form of adult-onset chronic open angle glaucoma (COAG), the clinical diagnosis of both groups are based on the presentation of visual field loss, glaucomatous changes of the optic nerve and optic nerve damage that is usually accompanied with an increased IOP. Apart from the clear differences in the age of diagnosis in these two groups of POAG, the condition in juvenile subjects is more severe, presenting with significantly higher IOPs (i.e., >40-50 mm Hg) that usually does not respond to drug treatment, and, therefore, lowering of the IOPs through multiple surgical interventions is a necessity (Johnson et al., 1993 ). In contrast, the late-onset form has a quite different phenotype, usually with a milder presentation, progressive development, moderate elevation of IOP and medical treatments often yield a satisfactory outcome (Jay et al., 1993). The painless progression often leads to a late diagnosis, when irreversible damage to the optic nerve has already occurred, thus complicating the prognosis of this type of POAG.

Although there is some controversy about the exact mode of inheritance in these two groups of eye condition, pedigree structure of the majority of families used in genetic linkage analysis clearly suggest that inheritance is autosomal dominant with an incomplete penetrance.

JUVENILE-ONSET PRIMARY OPEN ANGLE GLAUCOMA (JOAG)

A new page in the molecular genetic study of JOAG was opened in early 1993, when using a single large American family, (Sheffield et al., 1993). localized the first locus for this type of glaucoma. The locus was mapped to the 1q21-q31 region and named GLC1A (note: use of GLC1 symbol for all types of POAG has been approved by the HUGO Nomenclature Committee; the letters A, B, C, etc. will be assigned to each newly identified locus). After this initial report, the efforts of other investigators from the US and Europe were focused on testing additional glaucoma families from different genetic backgrounds.

Confirmation of this initial linkage was soon followed in another American JOAG family Richards, 1994, families with Irish, British and German backgrounds Wiggs et al., 1994 , two French families (Meyer et al., 1994) and one large Danish family (Graff et al., 1995).

Morissette et al. reported linkage in a multigeneration French-Canadian family with 142 members of whom 40 were affected. Based on the age of detection, the authors divided the glaucoma patients into two groups of JOAG and COAG. In this study, 36 subjects were diagnosed between the ages of 25 and 35 and, therefore, classified as having JOAG, while four subjects were diagnosed after the age of 40 and considered as COAG. Six other members were diagnosed with ocular hypertension and several other asymptomatic obligate carriers were also identified. The authors concluded that the GLC1A locus is responsible for both juvenile- and adult-onset POAG. A second family also presented with variable age of onset of POAG linked to the GLC1A locus. Twenty family members developed glaucoma between 11 and 51 years of age (median 36). A 35 year old healthy female had a severely affected daughter and therefore classified as a case of incomplete penetrance. Nine more normal family members aged from 14 to 66 had also inherited the affected haplotype.

Clinical features in the affected individuals from all of the families reported so far were very similar and conformed to the typical form of juvenile-onset primary open angle glaucoma. Despite the existing variability in the exact age of detection, the majority of the patients were diagnosed with glaucoma in childhood to early adulthood (average 18 years). The IOP was typically very high, often in the range of 40-50 mm Hg. Medical treatment was initially effective, but surgery was required to control the progress of glaucoma.

RECENT DEVELOPMENTS

A number of new mutations in the TIGR gene were presented recently (Annual Meeting of ARVO, The Association for Research in Vision and Ophthalmology, 1997). A total of 14 mutations in exon III and a number of new polymorphisms in exon I and/or 5' end of this gene were reported (Fingert et al., 1997). Additional mutations were also indicated by other groups in JOAG families from Italy Pirastu et al., 1997, Germany (Budde et al., 1997, France Brezin et al., 1997) and Canada. We have also identified a mutation in one family from Edinburgh, Scotland (Stoilova et al., 1997). The only deletion of 3 bp in exon III was reported in four families from a small southern Italian village where all individuals carry a common haplotype. This mutation most likely resulted from a founder effect with a common ancestral mutation (Pirastu et al., 1997). However, most of the reported sequence changes in the TIGR gene are missense mutations that are clustered in exon III.

One other interesting patient has been described who is hemizygous for the GLC1A region (Vollrath et al., 1997). This patient is 24 years of age and has no clinical evidence of glaucoma. The deletion of DNA markers in this subject included a 10 cM interval that contained the GLC1A locus. Therefore, it was indicated that the loss of function of one of the copies of the GLC1A gene (i.e., haploinsufficiency) in this patient would not be the cause of this type of glaucoma. However, it is still likely that this patient will develop glaucoma at a later stage of life and that the haploinsufficiency detected in this subject may still be adequate to cause the phenotype, a phenomena that has recently been reported for the chromosome 4q-linked Rieger syndrome (Flomen et al., 1997).

Another interesting piece of evidence is presented in a large French-Canadian pedigree that has previously been shown to be segregating for the GLC1A locus in which four subjects born to two affected parents inherited two copies of the affected GLC1A haplotype from their parents, but all were clinically normal for glaucoma. These patients were aged between 41 and 49 and they have already produced two clinically affected offspring who have inherited only a single affected haplotype. This observation indicated that homoallelic complementation of the affected haplotypes is a likely mechanism to account for these phenotypically normal homozygous affected carrying haplotype subjects. If these patients do not share the same TIGR mutation with other branches of the pedigree, a separate mutation in another part of the genome or mutation in one of the closely located genes within the GLC1A critical region could be responsible for this observation. This is likely as in the same pedigree, another two affected subjects (one with low-tension and another with angle-closure glaucoma) were described neither of whom carry the common affected haplotype. Therefore, this may indicate that for such a large pedigree, one should expect to see phenocopies for the glaucoma phenotype, perhaps more than once.

ADULT-ONSET CHRONIC OPEN ANGLE GLAUCOMA (COAG)

The adult-onset chronic open angle glaucoma (COAG) has the highest prevalence/incidence in Western societies. In these patients angle of the anterior chamber is normal and the optic nerve undergoes a characteristic atrophy that results in visual field loss and eventual blindness. Some patients have elevated IOP, but other confirmed open angle glaucoma patients have a `screening' IOP within the statistically normal range (Grosskreutz et al .,1994) . For this form of glaucoma, the onset is usually after the age of 40, but the majority of sufferers exhibit the disease even at later stages of life, usually after the ages of 50 or 60.

This has had a serious implication for diagnosis and proper treatment. As a consequence, it has been difficult to determine the exact mode of inheritance for this type of glaucoma, as the majority of these patients are either isolated cases, or by the time of first presentation, their parents are deceased and, therefore, no accurate clinical data or systematic ophthalmic information is available from previous generations. Therefore, autosomal dominant, autosomal recessive, X-linked and multifactorial modes of inheritance have been suggested for this condition Netland et al., 1993. However, in the majority of families that have been systematically studied, the autosomal dominant mode of inheritance with reduced penetrance has been suggested (Avramopolus et al.,1996).

PRIMARY CONGENITAL GLAUCOMA (PCG) OR BUPHTHALMOS

Primary congenital or infantile glaucoma (gene symbol, GLC3) is a specific inherited eye disorder that manifests itself in early childhood, usually within the first year of life, but may emerge up to the age of 3. The incidence is 1:1250 in the Gypsy population of Slovakia, 1:2500 in the Middle Eastern Turacli et al., 1992 and between 1:5000 and 1:10 000 in the Western countries. Although the familial forms of this condition have an autosomal recessive mode of inheritance, some apparent vertical transmission in some families may be explained by pseudo-dominance (Stoilov et al., 1997. Association of congenital glaucoma with chromosomal abnormalities of at least 17 different autosomes has also been reported in the literature Schinzel, A. 1984). Glaucoma in these instances is accompanied by dysmorphic features, multi-system abnormalities, developmental delay and abnormal results of cytogenetic studies. Therefore, it is likely that the nature of glaucoma in these subjects is secondary or the observed association of congenital glaucoma with these chromosomal abnormalities is coincidental.

Furthermore, genetic linkage study of a group of highly informative DNA markers selected from the reported regions with chromosomal abnormalities did not show any evidence for existence of a site in a group of families segregating for primary congenital glaucoma (Akarsu et al., 1996).

POAG AND ITS ASSOCIATED GENES

Association studies have suggested that, in addition to causative genes, there are at least 16 POAG-associated genes (Chakrabarthi et al., 2007). Most of these genes have been reported in single studies; a few of them have been investigated in multiple association studies, the findings of which are inconsistent. POAG-associated genes include apolipoprotein E (APOE; a potent modifier for POAG), optic atrophy P (OAP1), tumor protein p53 (TP53), tumor necrosis factor (TNF; reported to be associated with POAG in Chinese individuals) and cytochrome P450 1B1 (CYP1B1). CYP1B1 was initially suggested to be a modifier gene for the expression of MYOC in JOAG patients. However, recent studies have indicated that CYP1B1 may play an important role in JOAG, with possible monogenic association in French, Indian, and Spanish patients. Furthermore, mutations in CYP1B1 have been proposed as potential factors governing severity in POAG patients. CYP1B1 has also been identified as one of the three genetic loci linked to PCG (Table 1).

[pic]

The other two are GLC3B at chromosome locus 1p36 and GLC3C at chromosome locus 14q24.3-q31.1. Specific genes have not been linked yet to the GLC3B and GLC3C loci.

PCG is a form of glaucoma commonly referred to as infantile or congenital glaucoma. Although normally rare, it is the most common form of glaucoma in infants, with more than 80% of cases observed within the first year of life. This disorder is most likely due to developmental defects in the trabecular meshwork and the anterior chamber angle. The clinical findings in PCG patients typically include epiphora (watery eye), photophobia, corneal edema, and buphthalmolos (enlargement of the globe), which result from increased IOP. In PCG, elevated IOPs can rapidly lead to axonal loss and permanent loss of vision in untreated individuals. Sixty to eighty percent of cases involve both eyes, and males are more frequently affected than females (65% versus 35%, respectively). Inheritance is primarily autosomal recessive with variable penetrance. Ninety percent of cases are sporadic and pseudodominant transmission has been demonstrated in some families. Prevalence of PCG varies geographically from a rate of 1:10000 in Western countries to 1:1250 in the Romany population of Slovakia (Vasiliou and Gonzalez, 2008).

WDR36 Gene

WD40-repeats are stretches of 40 amino acids that contain tryptophan (W) and aspartic acid (D). WD-repeat–containing proteins comprise a large family found in all eukaryotes and are implicated in a variety of functions ranging from signal transduction and transcription regulation to cell cycle control and apoptosis. The underlying common function of all WD-repeat proteins is coordinating multiprotein complex assemblies, where the repeating units serve as a rigid scaffold for protein interactions. Based on sequence similarity, WDR36 was proposed to contain five (Mao et al., 2004) to eight (Monemi et al., 2005) WD40 repeats.

In addition, WDR36 contains a C-terminal UTP21 domain that is specifically associated with WD40 repeats(Bateman A et al.,2002) as well as sequence stretches that are characteristic for AMP-binding or which exhibit structural similarity to the C-terminal part of cytochrome cd119 Expression of WDR36 was shown in human ocular and nonocular tissues as well as in embryonic and adult mouse tissues.(Monemi et al.,2005) It has been suggested that WDR36 may be involved in T-cell activation(Mao et al.,2004) and recently, T-cell-mediated responses have been hypothesized to participate in glaucoma-associated optic nerve degeneration.(Bakalash et al .,2005) However, the exact physiological function of the protein and its role in glaucoma pathogenesis remain unclear.

WDR36 Mutation Pattern in different populations with POAG

Chinese Patients with POAG:

Nineteen sequence alterations including V714V Sequence Variant were identified, and eight of them were novel including two novel nonsynonymous SNPs (L240V and I713V). Except the common I264V polymorphism, no other previously reported disease-causing or disease-susceptibility mutations were found. The novel I713V mutation was observed in three (3.7%) patients with HTG. One intronic SNP, IVS5+30C>T (rs10038177), showed significantly higher frequency of minor allele T in HTG patients (16.5%) than in controls (1.3%; Odds ratio [OR]=15.0, p=7.9 x 10(-7), Bonferroni corrected p=1.5 x 10(-5)). Haplotype GTA, which is composed of rs13153937, rs10038177, and rs11241095, was significantly associated with HTG (OR=22.5, p=0.002, Bonferroni corrected p=0.013). Neither the individual SNPs nor haplotypes of WDR36 were associated with NTG or JOAG (Bonferroni corrected p>0.05).

Findings in this study suggest WDR36 to be associated with sporadic HTG but not with NTG or JOAG. Our results also suggest a different mutation pattern of WDR36 in the Chinese population from other ethnic populations (Fan et al., 2009).

Japanese Patients with POAG:

Twenty sequence alterations including V714V Sequence Variant were identified: 10 have already been reported (p.I264V, c.1494+90C>T, c.1494+143A>G, c.1609+89G>A, c.1775+89C>A, c.1965-30A>G, p.V714V, c.2170+217C>T, p.V727V, and c.2518+60G>C) and 10 were novel (p.D179D, p.Q270Q, p.M283R, c.898+63C>G, c.1074+20C>T, p.G459G, c.1884+26C>G, p.S664L, p.S664S, and p.P744P). One nonsynonymous amino acid change in exon 17, p.S664L, was identified in a patient with HTG. The frequency of the p.I264V variant was significantly higher in the HTG group than in the control group (p=0.01), but the frequency in the NTG group was not significantly different from the control group (p=0.12). The frequency of the c.1965-30A>G variant was also significantly higher in the HTG group than in the control group (p=0.03), but the frequency in the NTG group was not significantly different from the control group (p=0.06). CONCLUSIONS: One nonsynonymous variant, p.S664L, and the association of the allelic variants (p.I264V and c.1965-30A>G) in WDR36 and their prevalence in unrelated Japanese patients with HTG suggest that they are probably involved in the pathogenesis of HTG (Miyazawa et al., 2007).

German Population with POAG:

A total of 44 WDR36 allelic variants including V714V Sequence Variant were detected, including 14 nonsynonymous amino acid alterations, of which 7 are novel (P31T, Y97C, D126N, T403A, H411Y, H411L, and P487R) and 7 have been reported (L25P, D33E, A163V, H212P, A449T, D658G and I264V).

Of these 14 variants, 6 were classified as polymorphisms as they were detected in patients and control individuals at similar frequencies. Eight variants present in 15 patients (3.7%) but only 1 control individual (0.2%) were defined as putative disease-causing variants (P = 0.0005). Within this patient group, 12 (80%) presented with high and 3 (20%) with low intraocular pressure. Disease severity and age of onset showed a broad range.

The occurrence of several rare putative disease-causing variants in patients with glaucoma suggests that WDR36 may be a minor disease-causing gene in glaucoma, at least in the German population. The large variability in WDR36, though, requires functional validation of these variants, once its function is characterized (Pasutto F et al., 2008).

American population with POAG:

Thirty-two WDR36 sequence variants including V714V Sequence Variant were found in this population of patients with POAG. Nonsynonymous single-nucleotide polymorphisms (SNPs), including those previously described as "disease-causing" and "disease susceptibility," were found in 17% of POAG patients and 4% of control subjects. Although the distribution of WDR36 variants in the pedigrees did not show consistent segregation with the disease, the WDR36 sequence variants were found more frequently in patients with more severe disease. The results of this study suggest that abnormalities in WDR36 alone are not sufficient to cause POAG. The association of WDR36 sequence variants with more severe disease in affected individuals suggests that defects in the WDR36 gene can contribute to POAG and that WDR36 may be a glaucoma modifier gene (Hauser et al., 2006).

Australian Population with POAG:

To investigate in Australian patients with glaucoma and normal controls the prevalence and associated phenotype of the WDR36 D658G mutation, which has previously been suggested to be a disease-causing mutation in pedigrees with primary open-angle glaucoma (POAG). Case-control study. Two hundred forty-nine individuals with POAG and 217 age-matched control subjects were recruited through the Glaucoma Inheritance Study in Tasmania, Australia. Genomic DNA was amplified by polymerase chain reaction by intronic primers. The presence of the D658G variant was detected by BglI restriction enzyme digestion. The D658G variant was identified in four POAG cases (1.6%) and four control subjects (1.8%) (chi(2) = 0.04, P = .84). No control subject with the variant had a family history of glaucoma. The WDR36 D658G is a neutral variant in the Australian population. Further populations should be carefully assessed for this variant before concluding that WDR36 is a glaucoma gene (Hewitt AW et al., 2006).

MATERIALS AND METHODS

All the chemicals and enzymes used were of analytical grade and the plastic wares were procured from reputed vendors like Fermentas, SRL, Hi-media, Sigma Chemicals co. and Tarsons.

4.1 Blood sample collection:

Blood samples were collected from Karaikudi, Madurai and Kovilpatti eye hospitals by ophthalmologists. The patients were asked to complete an interview administered questionnaire. The questionnaire contains a) the personal details, b) precise information of the individuals (patient) disease.

After obtaining the informed consents, 2 mL of blood was obtained from the glaucoma patients along with control samples.

Institutional Ethical Committee (IEC) of Alagappa University has given necessary clearance for carrying out this project work.

4.2 Isolation of DNA:

DNA isolation from blood samples were performed using standard protocol (Jeffrey’s and Morton, 1987).

4.3 Reagents required:

4.3.1 a) 1X SSC

0.15 M NaCl - 0.44 g

15 mM Tri Sodium Citrate (pH 7.0) - 0.29 g

Mix both the solutions and make it for 50 mL with distilled water. The solution is then autoclaved and then stored at room temperature (RT).

4.3.2 b) 0.2 M Sodium Acetate

Dissolve 1.36 g of sodium acetate and make it for 50 mL with distilled water. The solution is then autoclaved and then stored at RT.

4.3.3 c) 10% Sodium Dodecyl Sulphate (SDS)

2.5 g of SDS was dissolved in 25 mL of autoclaved distilled water and stored in autoclaved reagent bottles at RT.

4.3.4 d) Equilibrated Phenol : Chloroform : Isoamylalcohol (25 : 24 : 1) (v/v/v) 4°C

Phenol, Chloroform and Isoamylalcohol are mixed together just before the isolation process in a 50 mL centrifuge tube. The mixtured is stored at 4°C.

4.3.5 e) Chloroform : Isoamylalcohol (24 : 1) (V/V) 4°C

Chloroform and Isoamylalcohol are mixed together just prior to the process in a 50 mL centrifuge tube. The mixture is stored at 4°C.

4.3.6 f) Ethyl Alcohol (Absolute)

This was commercially purchased from Tedia co. And stored in the refrigerator.

4.3.7 g) 70% Ethanol

Absolute ethyl alcohol - 70 mL

Autoclaved distilled water - 30 mL

4.4 Methodology:

2 mL of peripheral venous blood was collected from the bronchial vein at the elbow joint, using a disposable syringe (Dispovan). The blood was transferred to a sterile 2 mL vaccutainer tube that coated with Na2 EDTA. The tube was inverted for a few times and stored at 4°C till further processing.

100μL of blood sample was taken. Double volume of 1XSSC was added and centrifuge at 5000 rpm for 5 minutes. Decanted the supernatant and suspend the pellet with double the volume of 0.2M sodium acetate .15 μL of 10%SDS was also added. 1 mL of PCI was added and gently mixed the solution. Centrifuged at 10,000 rpm for 10 minutes. Supernatant was collected and 500 μL of Chloroform: isoamylalcohol (24:1) was added. Centrifuged at 10,000 rpm for 10 minutes.

After centrifugation, aqueous phase was collected and 500 μL of absolute ethanol was added. Centrifuged at 10,000 rpm for 10 minutes.

Supernatant was removed and 500 μl of 70% ethanol was added. Centrifuged at 10,000 rpm for 10 minutes. Decanted the supernatant and pellet was air-dried. 30 μL of nuclease free milli Q water was used for dissolving the DNA and stored at-200C.

4.5 Agarose gel electrophoresis of DNA samples:

The 0.7% agarose gel was seen to be appropriate for electrophoresis of human genomic DNA.

4.6 Reagents required:

4.6.1 a) 10 X Tris-Borate EDTA (TBE buffer)

Tris base - 108 g

Boric acid - 55 g

0.5 M EDTA - 40 mL (7.444 g/L)

Dissolve the above and make up to final volume to 500 mL with distilled water. The pH was adjusted to 8.3. The solution was autoclaved and stored at RT.

4.6.2 b) 6 X gel loading buffer

0.25% bromopehnol blue

0.25 % xylene cyanol

40% (w/v) sucrose in water

Dissolve the above contents and make upto 15 mL with autoclaved distilled water and stored at 4°C.

4.6.3 c) Ethidium bromide (10 mg / mL) (w/v)

Ethidium bromide - 10 mg

Autoclaved distilled water - 1 mL

4.7 Methodology:

0.80 g of agarose was weighed and added to 80 mL of 1 X TBE buffer. The mixture was boiled in Microwave oven to get uniform solution. The gel platform was sealed using cellophane tape and comb was placed in the appropriate slot. The boiled molten agarose was brought down to room temperature and poured into the sealed platform with the comb. The gel was left undisturbed to polymerise for about 30 minutes.

After the gel was set, the comb was carefully removed. The cellophane tape at ends was removed and the gel was placed in the electrophoresis tank that contains 1X TBE buffer. Caution should be taken such that the gel was completely immerged.

5 μL of the DNA sample along with 2 μL of loading dye was loaded into each well. Electrophoresis was carried out at 50 volts for 2 hours. Then the gel was stained in the EtBr solution for 10 minutes and then destained for another 10 minutes in distilled water. The gel was viewed under an UV trans-illuminator, ( UVitec, Lark innovative Inc) and the pictured was captured with the help of gel documentation unit.

4.8 Polymerase Chain Reaction (PCR) of Exon 3 region:

PCR was carried out to amplify a region in the Exon 3 of the human CYP1B1 gene, in which the polymorphism (Arg368His, G-A change) is present. The primers ordered based on the study done by (Kumar et al., 2007).

4.9 Reagents Required:

4.9.1 a) Primers

The primers were obtained in the lyophilized form from Ocimum Synthesis. Details of the primers are given in the table.

Details of the primers designed.

|S.No |Primer Name |Primer Sequence |Primer Length |GC% |Tm |

|1. |WDRF | 5’-TTCAAGATTGTAGAGTGTTTCTCTGA-3’ |26 mer |34% |58.5°C |

|2. |WDRR |5’-TGCAGCCTTGTAGACTGTTCA-3’ |21 mer |47% |57.9°C |

* 10 pmol of each primer was used

4.9.2 b) Working dNTP mix

dNTP was supplied in 10 mM concentration. It was stored at -20°C. Final working concentration of 0.25 mM was used for a single reaction set up.

4.9.3 c) MgCl2

MgCl2 was supplied in 25 mM concentration. It was stored at -20°C. This was diluted so as to get a final concentration of 2 mM in the PCR reaction mixture.

4.9.4 d) Taq polymerase

Taq polymerase was obtained at a concentration of 1 U/µL and was stored at -20°C.

4.10 Methodology:

The mixing of different PCR reagents was carried out in a sterile condition and on ice. Total reaction volume was set to 20 µL for each reaction. The PCR components were added to the PCR tube in a stepwise manner. The various components and their respective volumes are represented below in the following table

4.10.1. PCR Reaction

|Ingredients |Stock |Working Stock |Amount Taken |

|Sterile milli Q water | | |11.5 µL |

| PCR Buffer |10 X |1 X | 2.0 µL |

|dNTPs |10 mM |0.25 mM | 0.5 µL |

|MgCl2 |25 mM |2 mM | 2.0 µL |

|WDRF |100 Pico Moles |10 Pico Moles | 1.0 µL |

|WDRR |100 Pico Moles |10 Pico Moles | 1.0 µL |

|Taq DNA polymerase |10 U/10 µL |1 U/ 1µL | 1.0 µL |

|Template | |~50 ng | 1.0 µL |

The typical amplification cycle is represented below.

1. Initial Denaturation : 95° C for 3 minutes

2. Denaturation : 95° C for 30 seconds

3. Annealing : 57° C for 30 seconds 30 cycles

4. Extension : 72° C for 60 seconds

5. Final Extension : 72° C for 5 minutes

6. Holding Temperature : 4° C

The annealing temperature was standardized to 57° C.

4.11 Agarose Gel Electrophoresis:

After each PCR reaction the products were checked by electrophoresis on a 2% agarose gel. 1.6 g of agarose was melted in 80 mL of 1x TBE buffer. 3 µL of the reaction products were loaded with 2 µL of loading dye to check for the amplification.

4.12 RFLP analysis:

Genotyping was performed by RFLP (Restriction Fragment Length Polymorphism) analysis. PCR amplicons were digested with Hin1II restriction enzyme. In homozygous normal, Hin1II enzyme recognize 5' C A T G 3‘ site and produce fragment (478 bp).

In heterozygous mutant, Hin1II produce three fragments (167 bp, 165 bp and 146 bp). In homozygous mutant, Hin1II will produce three fragments (167 bp, 165 bp and 146 bp).

4.13 RFLP Reaction condition

Hin1II was obtained from MBI Fermentas in the concentration of 10 U/ µL. Stored at -20 °C.

10 X buffer – Diluted to 1 X in the reaction mixture.

The digestion reaction is represented as follows

|Ingredients |Stock concentration |Working concentration |Amount Taken |

|Sterile milli Q water | | |0.8 µL |

|Tango Buffer |10 X |1 X |1.0 µL |

|Hin1II restriction enzyme |10 U/ µL |2 U |0.2 µL |

|PCR Products | | |8.0 µL |

The reaction volume was set up to 10 µL and the mixture was incubated at 65° C for 4 hours.

4.14 Agarose Gel for Analysis of the Digested Amplicons

The digested amplicons were analyzed by electrophoresis on a 2% agarose gel. 2.4 g of agarose was melted in 80 mL of 1 X TBE buffer. 8 µL of the digested samples were mixed with 2 µL of loading dye which is sufficient for the analysis of digestion. The digested DNA sample in the gel was viewed under UV trans-illuminator and photographed.

RESULT

Glaucoma is a term used to refer to a heterogeneous group of optic neuropathies that cause a progressive loss of vision. WDR36 was the recent glaucoma gene discovered. It plays a very important role in the pathogenesis of autosomal dominant juvenile glaucoma and is involved in a small but significant subset of adult onset POAG. This study conceived for the detection of WDR36 mutation (V714V) in the coding exon 18, among south Indian glaucoma patients. The patient group comprised of 20 unrelated with POAG patients ranged in the age from 40- 84 years at the time of this study. There were 10 unrelated individuals with out any evidence of glaucoma as a control group also recruited for the study.

Genomic DNA was isolated from the patients and the control groups. An aliquot of genomic DNA was loaded on a 0.8% agarose gel prestained with Ethidium Bromide. PCR was carried out to amplify the coding region of exon 18 of WDR36 gene, which amplifies the 478bp amplicon, which was confirmed on 2% agarose gel.

All the PCR products of patients as well as the controls were subjected to digest with the Hin1II enzyme. Digested products were analyzed on a 2 % agarose gel to find the presence of hetero/ homozygous nature. The gain of Hin1II restriction site cleaves in to 167 bp 165 bp and 146 bp PCR products were as the loss of restriction site remains intact of 478 bp.

In this study the 20 patients and normal controls were digested with Hin1II enzyme remains intact, thus concludes that no sequence changes in the coding region of exon 18 of WDR36 was found in 20 unrelated glaucoma patients and 10 normal control subjects.

This indicates that the prevalence of V714V mutation is less in south Indian glaucoma patients, and concludes the inconsistency of the V714V with other ethnic groups. The allelic frequency of this sequence change did not differ significantly between the western POAG populations.

The allelic and genotype frequency result of V714V of WDR36 is not significant in POAG patients hail from the south Tamilnadu.

DISCUSSION

To understand the distribution of WDR36 V714V mutation in JOAG patients with normal controls were analyzed by PCR-RFLP.V714V mutation that have been identified in patients with adult onset POAG was detected as a significant pathological mutation in other ethnic population. The V714V coding region falls on exon 18 of WDR36 gene plays an important role in POAG – the study was carried out to detect the particular mutation. PCR-RFLP is the simple and easiest method to identify the known mutation or previously reported mutations.

In this study Hin1II restriction enzyme was used to digest the 478 bp PCR product of exon 18 of WDR36. The gain of the site indicates 254bp and 224 bp products on 1 % agarose gel, however the loss of site remain intact of the 20 POAG patients analyzed with PCR-RFLP none showed presence of V714V mutation of WDR36 gene.

This concludes that the mutation would have occurred in other exons of WDR36 or other genes that includes OPTN and MYOC contrarily the presence of V714V mutation is not a predominant in POAG of south Indian population. In conclusion V714V mutation of WDR36 gene is not a causative mutation for the POAG in South Indian population.

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