Ординатура / Офтальмология / Английские материалы / Mechanisms of the Glaucomas_Shields, Tombran-Tink, Barnstable_2008

in low-tension or normal-pressure glaucoma individuals (3), the WD40-repeat 36 gene (WDR36) identified at chromosome 5q22.1 as the GLC1G locus (4) and myocilin (MYOC; OMIM 601652) (2). To date, these genes account for approximately 10% of mutations identified in OAG, indicating that other genes must also be involved in its aetiology. This chapter will outline a description of the gene MYOC and focus on the known role of the most prevalent mutation (glutamine 368STOP) so far identified in this gene in adult OAG.

IDENTIFICATION OF THE MYOCILIN GENE

Myocilin (MYOC) was the first causative gene to be identified in individuals with OAG. The gene was identified through a combination of two different approaches. In the first approach, linkage analysis was undertaken using pedigrees segregating with the juvenile form of open-angle glaucoma (JOAG). Individuals with JOAG typically present with a similar clinical but more severe and earlier age of disease presentation compared to the adult form of OAG. Using this approach, successful linkage analysis was achieved using three large JOAG families that identified chromosome region 1q21–31 as the likely disease gene-containing region (5). This region was still relatively large with many putative genes in the region. Help to identify the causative glaucoma disease gene came from independent studies, where the pathophysiology of glaucoma was being explored through experiments with trabecular meshwork (TM) cells. These studies involved the growth of human TM cells in culture that were subsequently subjected to glucocorticoid stimulation to mimic the conditions of steroid-induced ocular hypertension (OHT) and induce changes in gene expression. Success in this experimental design led to the identification of the TM-induced glucocorticoid response (TIGR) protein (6). Cloning of the TIGR cDNA from several human tissues (6–9) of the eye allowed mapping of the gene to chromosome 1q, the same region as identified through JOAG linkage analysis. Mutation analysis of the TIGR gene in the JOAG individuals identified from the original linkage study (5) revealed a number of DNA alterations within this gene. Extension of this study to two adult onset OAG families also revealed gene alterations in individuals in these families, indicating that this gene was also involved in adult onset OAG (2). The identified gene has had several names including GLC1A, GPOA, HGNC:7610, JOAG, JOAG1, TIGR, myocilin, and MYOC. However, the approved gene symbol is MYOC (http://www.genenames.org/), located at the chromosome 1q23-24 region between 168,336,216 base pairs (bp)–168,353,430 base pairs (http://www.hapmap.org) on this chromosome.

RNA expression studies using northern blot analysis revealed that MYOC was expressed as a 2.3-kb transcript in most tissues of the eye as well as in muscle, papillary sphincter, skeletal muscle, heart, and other tissues. The gene encodes a 58-kD, 504 amino acid protein (10). Genomic analysis reveals it to be 17,215 bp in size with the gene consisting of three exons of 604, 126 and 782 bp.

MUTATION ANALYSIS OF THE MYOC GENE IN OAG

Large-scale mutation screening of the MYOC gene in adult OAG individuals was first reported in 330 unrelated OAG cases and 471 controls (no glaucoma) in a US study (2). This confirmed that MYOC mutations were present in 3.9% of OAG patients

but only in 0.2% of controls (a statistically significant difference). Many studies have now been undertaken in various adult OAG populations of different ethnicity, and it is clear that a wide range of disease-causing variants exist within the MYOC gene in these individuals. The spectrum and definition of what constitutes a disease-causing variant as opposed to a polymorphism or non-disease causing variant in MYOC has been eloquently and extensively detailed in two reviews (11,12). However, it is now clear that the original definition (13), whereby a disease-causing variant should (i) alter the MYOC amino acid sequence, (ii) be present in one or more glaucoma subjects, (iii) be present in less than 1% of the general population and (iv) be absent in normal controls was likely too restrictive. A more relaxed definition of a disease-causing variant has been proposed in reference (14), where (i) there is alteration of the amino acid sequence and (ii) the variant is more commonly observed in patients with OAG than in controls. Therefore a disease-causing variant needs to be either completely absent from the control population or significantly more common in the OAG population (14) and should segregate with disease in families.

Of the 72 publicly reported disease-causing variants (mutations) in the MYOC gene, the vast majority of the these (64) are missense/nonsense mutations, five are regulatory, two are small indels and one is a gross insertion (http://www.hgmd.cf.ac. uk/ac/index.php). Approximately 90% of the missense/nonsense changes are located within the carboxy-terminus olfactomedin-homology (Olf) domain [amino acids (aa) 245–504] of exon 3 of the MYOC gene, suggesting that this region plays a major regulatory role in OAG (15). Expression of MYOC is known to occur in the TM and ciliary body, and this has led to speculation that MYOC is involved in controlling the process of intraocular pressure (IOP) by either obstructing aqueous outflow or through muscle-related ciliary body mechanisms.

Interestingly, previous studies of OAG individuals from different ethnic backgrounds have indicated a similar worldwide prevalence of MYOC disease mutations. In Caucasians (including Europe, USA, Canada, Australia and India), African Americans and Japanese OAG cases, approximately 2–4.4% of individuals present with a mutation in the MYOC gene (13,16–22), whereas in Chinese OAG patients, prevalence is slightly lower at 1.1–1.8% (23–26). This has led to speculation that the relatively conserved prevalence of MYOC mutations worldwide reflects additional control mechanisms operating at the genetic level.

If only the MYOC sequence changes that have been classified as mutations in different populations are considered, then the vast majority of these mutations occur as single cases, suggesting that these changes represent private or rare mutations. There also appears to be little overlap between different disease-causing variants in different ethnic groups, with only Gly252Arg, Gly367Arg and Pro370Leu being present in both Caucasian and Asian populations and only Thr293Lys, Thr377Met and Glu352Lys being present in Caucasian and African populations. No one single mutation has so far been reported to be present in all three different ethnic groups (12).

It is clear that a minority of MYOC mutations present much more frequently in any one of the ethnic groups compared to others and that these most likely constitute disease-causing mutation hotspots in OAG. The most prevalent MYOC mutations identified in each ethnic population appear to account for approximately 1–2% of

disease mutations found in OAG. In Asian populations, these mutations are represented by the changes of Arg46Stop in 7/493 (1.4%), Asp208Glu in 6/341 (1.8%) and Thr353Ile in 6/353 (1.7%) OAG individuals (13,24,27,28). In African and African American populations, these mutations are represented by the changes of Arg342Lys in 2/90 (2.2%), Glu352Lys in 6/351 (1.8%) and Asp380Asn in 2/90 (2.2%) of OAG individuals (13,20,22,29,30). In Caucasians, the main mutations are the Gln368Stop in 51/2943 (1.7%) and Pro370Leu in 6/704 (0.9%) OAG individuals (13,14,18–20,29–36). However, of all the highly prevalent mutations described, the Q368STOP mutation appears to be restricted mainly to adult onset OAG families or in families where there is a mix of both juvenile and adult onset OAG. This contrasts to a number of other mutations described for the MYOC gene that are found either only in the juvenile form of disease or rarely in the adult onset form of disease.

THE Q368STOP MUTATION

Given the relative paucity of common mutations in adult onset OAG, it is perhaps worth considering what we know about the Q368STOP mutation – the most common and well-researched adult OAG mutation currently described in the literature. This may allow us to better understand the role of myocilin in OAG and ultimately allow us to learn more about disease pathways involved in disease and thus to ultimately improve treatment strategies for patients.

A single heterozygous C->T base change at codon exon 368 in exon 3 of the MYOC gene results in the Gln368Stop (Q368STOP) change and this accounts for approximately half (1.7–1.9%) of all mutations so far identified in this gene in Caucasian populations (13,37). This mutation has also been reported to occur in 5/117 individuals (4.27%) in a Swiss OAG study (35) and 12/237 OAG individuals (5%) in a French study (38), suggesting that some regional hotspots may exist for this mutation. The Q368STOP mutation appears to be specific for Caucasians of European origin, as it has not been reported in Japanese (13,28,39–43), Korean (27), Chinese (23,24) or Indian populations (16,17,18). However, a single case has been reported in an African American with OAG (13) although this appears to be at odds with most other studies of OAG individuals in African populations (22,44). The most likely explanation for this observation is that it reflects admixture of the African population with individuals of European descent. Previous studies have estimated that the contribution of European genes into individuals of African American descent in the USA varies from 17 to 22.5% depending upon the city population under study (45).

EVIDENCE OF A FOUNDER EFFECT FOR THE Q368STOP MUTATION IN MYOC

The identification of the Q368STOP mutation in OAG individuals from several different Caucasian populations including American, Canadian, European and Australian suggested either a common ancestral founder for this mutation or separate de novo events occurring in each population (13). A common origin for this mutation was first suggested based on allele sharing of the four closely linked markers (MY5, MY3, D1S1619 and D1S2815) to this gene (13). Further analysis in French OAG patients

confirmed allele sharing in MYOC neighbouring microsatellite markers (38). However, in both cases, a disease haplotype could not be fully established for Q368STOP, as these were cohort rather than family-based studies.

Additional evidence to support a founder effect for the Q368STOP mutation came from several family-based studies. These included allele sharing in three distantly related Scottish OAG families (46), identification of a disease haplotype in French Canadian OAG families from Quebec (20), and a common disease haplotype in 15 OAG families collected from south eastern Australia through the Glaucoma Inheritance Study in Tasmania (GIST) (47).

To establish whether the haplotypes identified in each Caucasian population were shared between OAG individuals in different countries, genotyping was undertaken using microsatellite markers in Australian and French Canadian OAG families. The four microsatellite markers, My5, My3, D1S2815 and D1S1619 spanning a 0.14-Mb region of the GLC1A locus, previously described as defining the Q368STOP disease haplotype in Australian OAG families (47), were genotyped. Three members of a French Canadian family (CT), two unrelated French Canadian individuals with either OAG or OHT (20), as well as nine members from a Tasmanian family (GTAS2) (47) were analysed. A shared allelic pattern of 2-2-4-2 that had previously been described as the Q368STOP disease haplotype in Australian OAG families (47) was also identified in the French Canadian families. This finding of a shared haplotype for the Q368STOP mutation in both French Canadian and Australian populations provided additional support for a global disease haplotype for the Q368STOP mutation in Caucasian individuals of European descent (48). It also suggested that the most likely origin of this mutation was from a founder who originated from either central or northern France, whose descendants then spread across Europe with subsequent dispersion to New World countries. This observation may explain why a higher prevalence of this mutation has been reported in French (38) as well as Swiss populations (35).

THE Q368STOP AND GLAUCOMA PHENOTYPE

A number of reports have described OAG individuals with the Q368STOP mutation as having a ‘mild’ or late onset of disease that is essentially indistinguishable from OAG individuals without this mutation (2,20,30,49,50). In one report, diagnosis of a patient was not made until age 78 years (19). However, the mean age of diagnosis of OAG individuals with this mutation shows wide variation, ranging from 28 to 77 years with a mean age of diagnosis of 56 years in 10 studies (see Table 1). When the mean age of diagnosis of OAG individuals with the Q368STOP mutation (57 years) was compared to that of OAG individuals without a MYOC mutation (48 years), there was no significant difference between the two groups, whereas when compared to OAG individuals with other MYOC mutations (32 years), there was a significant difference (38) (see Table 1). However, this contrasts to another study (51) where individuals with either OAG or OHT and the Q368STOP mutation were diagnosed at a significantly younger mean age of 52.4 years (standard deviation of ±12.9 years) compared to OAG or OHT individuals with no Q368STOP mutation who were diagnosed at a mean age of 62.3 years (standard deviation of ±13.7 years) (p = 0.01) (see Table 1). Also, the Q368STOP mutation has been reported to be present only in families with both juvenile

Table 1

Reported Age of Diagnosis and Intraocular Pressure in Open Angle Glaucoma Individuals with and without the Q368STOP Mutation of Myocilin

SD, Standard deviation; SE, standard error.

aTotal number of individuals/number of individuals where an IOP measurement was obtained. -Indicates no Q368STOP mutation and + indicates presence of Q368STOP mutation.

and late onset OAG individuals at a mean age of diagnosis of 37 years (range 27–49 years) (33). Although these findings appear at odds, the inclusion of OHT individuals in the study by Craig et al. (51) may have resulted in an earlier age of reported onset and thus reflect a methodological, rather than a clinical difference. Overall, there does appear to be an increase in disease penetrance for this mutation with age. In two studies, this penetrance has been estimated at 72% at age 40 and 78–82% at ages 65–70 years (30,51). Therefore, it is likely that the age of an individual with this mutation is an important predictor of their final likelihood of developing OAG.

If mean peak IOP of OAG individuals with the Q368STOP mutation is considered then a pattern of presentation similar to age of diagnosis is evident. In this case, the mean peak IOP in OAG individuals has been reported to range from 21 to 70 mmHg (see Table 1). The IOP appeared to have a broader range compared to several other MYOC mutations including 396INS397, Tyr437His, Ile477Asn, Asp480Lys, Ile499Phe, Gly376Arg and Thr438Ile, where IOPs of between 35 and 52 mmHg (49,52) have been reported in OAG individuals (62 mmHg) without a MYOC mutation (51). Additionally, OAG individuals with the Q368STOP mutation appear to require more frequent glaucoma drainage surgery relative to OAG individuals with other MYOC mutations or OAG individuals without MYOC mutations (35,51). On the other hand, mean peak IOP in individuals with the Q368STOP mutation has been shown to be comparable to that of other MYOC mutations (Gly364Val and Thr377Met) (49,52), and in one study, an OAG individual with the Q368STOP mutation has been shown to present with no elevated pressure (53).

Thus, although the MYOC gene has been implicated in the control of IOP due to its expression within the TM of the eye (6,7,9,54–56), its exact function still remains unknown. To compound this situation, a recent study using variance components analysis indicated that the Q368STOP mutation accounted for approximately half the genetic variance of the quantitative trait of maximum cup-to-disc ratio but only 20% of the genetic variance for maximum IOP in a large Tasmanian family (GTAS2) (57).

The wide variability in age of diagnosis as well as in mean peak IOP in OAG individuals with the Q368STOP mutation and lack of a simple autosomal-dominant inheritance pattern in OAG pedigrees with this mutation suggests that other factors also likely influence final OAG phenotype. These factors may either directly or indirectly interact with MYOC to modify its risk associated with final disease presentation. This suggests that the MYOC gene may have effects that extend beyond that of IOP and that its role in glaucoma is more complex than originally envisaged.

THE Q368STOP IN UNAFFECTED INDIVIDUALS

The Q368STOP mutation has also been previously described in the general population in individuals where there are no apparent clinical features of OAG. However, prevalence is low at 1/505 (0.2%) (49) and 1/380 (0.26%) (2) American Caucasian individuals and 2/2142 (0.09%) Australian Caucasian individuals from the population-based epidemiological eye study: the Blue Mountains Eye Study (BMES) (58). To gain a better understanding of its occurrence in the general population, further analysis was undertaken on the two individuals identified from the Australian study. Both individuals were identified as males, aged 56 and 72 years and were

unrelated. There was no indication of glaucoma at clinical examination, with the younger individual presenting with a normal IOP (16,16) and normal fields although he did report a positive family history of glaucoma on his father’s side. The 72 year old also had normal IOP (9,9) and normal fields and no reported family history. In both cases, genotype analysis revealed a shared allelic pattern of 2-2-4-2 at the four microsatellite markers; My5, My3, D1S2815 and D1S1619, previously described as defining the global Q368STOP disease haplotype in OAG (47). The likelihood against these two individuals sharing alleles at these four markers by chance was significant (p = 0.001) and suggested that the mutation most likely arose from a common founder rather than as two separate ‘de novo’ events. It should also be considered that given the age of these two individuals, there is always the possibility that they may go on to develop OAG later on in life.

THE Q368STOP AND MODIFIER GENES

Several reports have now detailed what appears to be either a lack of segregation of the Q368STOP mutation with disease or the presence of genetic heterogeneity within OAG families (20,30,47,50,51). For instance, in a large French Canadian family (CT) where 15 individuals had the Q368STOP mutation, only four presented with OAG and two with OHT (20). In another study, only 9 of 19 Q368STOP mutation carriers were identified with either glaucoma or OHT in a large Tasmanian family (GTAS2) (51). In both cases, it was clear that the Q368STOP mutation was unable to account for the presence of all OAG cases in each family.

In the Tasmanian family GTAS2, it was clear that there were an additional 18 OAGaffected individuals in this family without the Q368STOP mutation, thus suggesting the presence of additional disease genes in the family (47). Through the use of a Markov Chain Monte Carlo method, a second autosomal-dominant glaucoma gene locus was localized to a 9cM region on the short arm of chromosome 3 between markers D3S1298 and D3S1289 (59). This region did not overlap with any previously described locus for OAG and provided evidence of a new locus on the short arm (3p21–22) of chromosome three, now officially designated as GLC1L (http://www.genenames.org/). Interesting, a multiplicative relative risk model identified a positive association between the disease haplotype at the GLC1L locus and the Q368STOP mutation of MYOC in affected individuals from this family, suggesting that the relative risks for the two loci were super-multiplicative with an odds ratio of 12.8 (59).

The majority of OAG individuals in the family GTAS2 who presented with a putative disease haplotype at D3S1298 and D3S1289 also had the Q368STOP mutation in MYOC. Through the use of the Kaplan–Meier estimator, individuals who carried the putative disease haplotype at the 3p21–22 region and the Q368STOP mutation in MYOC tended to have OAG at an earlier age of disease onset, at age 58 years, compared to those individuals without the chromosome three haplotype, who had a median age of onset of 80 years. These findings suggested that the disease gene at the GLC1L locus was most likely a modifying gene of MYOC rather than MYOC being a modifier of GLC1L. However, this does not rule out the possibility that MYOC may also act as a modifier gene or that other genes also modify MYOC.

CONCLUSION

The study of the Q368STOP mutation of MYOC has revealed that the ultimate goal of being able to offer predictive testing to individuals with a family history of OAG or to the general population and predict risk of disease appears to still be some way off at present. However, some laboratories around the world are already offering such gene tests, and one laboratory is already offering prenatal diagnosis. The complications of a multifactorial complex disease indicate that dealing with one gene in isolation provides only a single piece in a jigsaw, in what is increasingly becoming a picture with many pieces.

Our knowledge of the role of genes in OAG is increasing, albeit slowly, and the investigation of mutations such as Q368STOP will ultimately allow us to explore the effects of genes upon individual phenotypic traits in OAG. It is likely that in future, it will be necessary to undertake disease stratification based not only on OAG phenotype but also on genotype and that the combination of the two will provide the best indicator of glaucoma risk for an individual.

REFERENCES

1.Tielsch, J.M., Sommer, A., Katz, J., Royall, R.M., Quigley, H.A. and Javitt, J. (1991) Racial variations in the prevalence of primary open-angle glaucoma. The Baltimore Eye Survey. JAMA., 266, 369–367.

2.Stone, E.M., Fingert, J.H., Alward, W.L., Nguyen, T.D., Polansky, J.R., Sunden, S.L., Nishimura, D., Clark, A.F., Nystuen, A., Nichols, B.E., Mackey, D.A., Ritch, R., Kalenak, J.W., Craven, E.R. and Sheffield, V.C. (1997) Identification of a gene that causes primary open angle glaucoma. Science, 275, 668–670.

3.Rezaie, T., Child, A., Hitchings, R., Brice, G., Miller, L., Cocao-Prados, M., Heon, E., Krupin, T., Ritch, R., Kreutzer, D., Crick, R.P. and Sarfarazi, M. (2002) Adult-onset primary open-angle glaucoma caused by mutations in optineurin. Science, 295, 1077–1079.

4.Monemi, S., Spaeth, G., Dasilva, A., Popinchalk, S., Ilitchev, E., Liebmann, J., Ritch, R., Héon, E., Crick, R.P., Child, A. and Sarfarazi, M. (2005) Identification of a Novel AdultOnset Primary Open Angle Glaucoma (POAG) Gene on, 5q22.1. Hum. Mol. Genet., 14, 725–733.

5.Sheffield, V.C., Stone, E.M., Alward, W.L., Drack, A.V., Johnson, A.T., Streb, L.M. and Nichols, B.E. (1993) Genetic linkage of familial open angle glaucoma to chromosome, 1q21–q31. Nat. Genet., 4, 47–50.

6.Polansky, J.R., Fauss, D.J., Chen, P., Chen, H., Lutjen-Drecoll, E., Johnson, D., Kurtz, R.M., Ma, Z.D., Bloom, E. and Nguyen, T.D. (1997) Cellular pharmacology and molecular biology of the trabecular meshwork inducible glucocorticoid response gene product.

Ophthalmologica, 211, 126–139.

7.Kubota, R., Noda, S., Wang, Y., Minoshima, S., Asakawa, S., Kudoh, J., Mashima, Y., Oguchi, Y. and Shimizu, N. (1997) A novel myosin-like protein (myocilin) expressed in the connecting cilium of the photoreceptor, molecular cloning, tissue expression, and chromosomal mapping. Genomics„ 41, 360–369.

8.Nguyen, T.D., Chen, P., Huang, W.D., Chen, H., Johnson, D. and Polansky, J.R. (1998) Gene structure and properties of TIGR, an olfactomedin.related glycoprotein cloned from glucocorticoid-induced trabecular meshwork cells. J. Biol. Chem., 273, 6341–6350.

9.Ortego, J., Excribano, J. and Cocao-Prados, M. (1997) Cloning and characterization of subtracted cDNAs from a human ciliary body library encoding TIGR, a protein involved

in juvenile open angle glaucoma with homology to myosin and olfactomedin. FEBS Lett., 413, 349–353.

10.Fingert, J.H., Ying, L., Swiderski, R.E., Nystuen, A.M., Arbour, N.C., Alward, W.L.M., Sheffield, V.C. and Stone, E.M. (1998). Characterization and comparison of the human and mouse GLC1A Glaucoma Genes Characterization and Comparison of the Human and Mouse GLC1A Glaucoma Genes. Genome Res., 8, 377–384.

11.Fingert, J.H., Stone, E.M., Sheffield, V.C. and Alward, W.L. (2002) Myocilin glaucoma.

Surv. Ophthalmol., 47, 547–561.

12.Gong, G., Kosoko-Lasaki, O., Haynatzki, G.R. and Wilson, M.R. (2004) Genetic dissection of myocilin glaucoma. Hum. Mol. Genet., 13, Spec No 1:R91–102.

13.Fingert, J.H., Heon, E., Liebmann, J.M., Yamamoto, T., Craig, J.E., Rait, J., Kawase, K., Hoh, S.T., Buys, Y.M., Dickinson, J., Hockey, R.R., Williams_Lyn, D., Trope, G., Kitazawa, Y., Ritch, R., Mackey, D.A., Alward, W.L., Sheffield, V.C. and Stone EM. (1999) Analysis of myocilin mutations in 1703 glaucoma patients from five different populations. Hum. Mol. Genet., 8, 899–905.

14.Alward, W.L., Kwon, Y.H., Khanna, C.L., Johnson, A.T., Hayreh, S.S., Zimmerman, M.B., Narkiewicz, J., Andorf, J.L., Moore, P.A., Fingert, J.H., Sheffield, V.C. and Stone EM. (2002) Variations in the myocilin gene in patients with open-angle glaucoma. Arch. Ophthalmol., 120, 1189–1197.

15.Gobeil, S., Letarte, L. and Raymond, V. (2006) Functional analysis of the glaucoma-causing TIGR/myocilin protein: integrity of amino-terminal coiled-coil regions and olfactomedin homology domain is essential for extracellular adhesion and secretion. Exp. Eye Res., 82, 1017–1029.

16.Kanagavalli, J., Krishnadas, S.R., Pandaranayaka, E., Krishnaswamy, S. and Sundaresan, P. (2003) Evaluation and understanding of myocilin mutations in Indian primary open angle glaucoma patients. Mol. Vis., 9, 606–614.

17.Sripriya, S., Uthra, S., Sangeetha, R., George, R.J., Hemamalini, A., Paul. P.G., Amali, J., Vijaya, L. and Kumaramanickavel, G. (2004) Low frequency of myocilin mutations in Indian primary open-angle glaucoma patients. Clin. Genet., 65, 333–337.

18.Mukhopadhyay, A., Acharya, M., Mukherjee, S., Ray, J., Choudhury, S., Khan, M. and Ray, K. (2002) Mutations in MYOC gene of Indian primary open angle glaucoma patients. Mol. Vis., 8, 442–428.

19.Wiggs, J.L., Allingham, R.R., Vollrath, D., Jones, K.H., De La Paz, M., Kern, J., Patterson, K., Babb, V.L., Del Bono, E.A., Broomer, B.W., Pericak-Vance, M.A. and Haines, J.L. (1998) Prevalence of mutations in TIGR/Myocilin in patients with adult and juvenile primary open-angle glaucoma. Am. J. Hum. Genet., 63, 1549–1552.

20.Faucher, M., Anctil, J.L., Rodrigue, M.A., Duchesne, A., Bergeron, D., Blondeau, P., Cote, G., Dubois, S., Bergeron, J., Arseneault, R., The Quebec Glaucoma Network., Morisette, J. and Raymond, V. (2002) Founder TIGR/myocilin mutations for glaucoma in the Quebec population. Hum. Mol. Genet., 11, 2077–2790.

21.Colomb, E., Nguyen, T.D., Bechetoille, A., Dascotte, J.C., Valtot, F., Brezin, A.P., Berkani, M., Copin, B., Gomez, L., Polansky, J.R. and Garchon, H.J. (2001) Association of a single nucleotide polymorphism in the TIGR/MYOCILIN gene promoter with the severity of primary open-angle glaucoma. Clin. Genet., 60, 220–225.

22.Challa, P., Herndon, L.W., Hauser, M.A., Broomer, B.W., Pericak.Vance, M.A., Ababio.Danso, B. and Allingham, R.R. (2002) Prevalence of myocilin mutations in adults with primary open-angle glaucoma in Ghana, West Africa. J. Glaucoma., 11, 416–420.

23.Lam, D.S., Leung, Y.F., Chua, J.K., Baum, L., Fan, D.S., Choy, K.W. and Pang, C.P. (2000) Truncations in the TIGR gene in individuals with and without primary open-angle glaucoma. Invest. Ophthalmol. Vis. Sci., 41, 1386–1391.