COL1A1 and COL2A1 Genes and Myopia Susceptibility: Evidence of Association and Suggestive Linkage to the COL2A1 Locus

Abstract

purpose. Collagen involvement in myopia development via scleral remodeling is well-known. Recently, COL1A1 and COL2A1 gene polymorphisms were reported to be associated with high-grade and common myopia, respectively. This study was conducted to investigate whether these collagen genes are associated and/or genetically linked with myopia in large Caucasian family datasets.

methods. High-grade myopia was defined as ≤−5.00 D. Two independent datasets comprising 146 (Duke) and 130 (Cardiff) families with high-grade myopia participated in the association study. Allelic discrimination assays were performed on tagging SNPs for COL1A1 and COL2A1. The pedigree disequilibrium test (PDT) and the association test in the presence of linkage (APL) were used for association analyses. Linkage analyses for COL2A1 locus markers were performed with the Fastlink and Merlin programs in conjunction with data obtained from our collaborative whole-genome linkage study (254 families).

results. Significant association was identified between five SNPs (rs1034762, rs1635529, rs1793933, rs3803183, and rs17122571) of the COL2A1 locus and high-grade myopia (P < 0.045, minimum (min) P = 0.008) and with myopia status set at ≤−0.50 or −0.75 D (min P = 0.004) in the Duke dataset. The SNP rs1635529 also showed significant association in the Cardiff dataset (≤−5.00 D, min P = 0.004; ≤−0.50 D, min P = 0.007). Linkage analyses showed suggestive linkage to the COL2A1 locus on 12q. No association was found between COL1A1 SNPs and any degree of myopia.

conclusions. The COL2A1 gene was associated with high-grade myopia in two independent Caucasian family datasets. COL1A1 gene polymorphisms were not associated with myopia in our dataset, indicating possible heterogeneity across different ethnicities.

Genetic involvement in susceptibility to myopia is well recognized. ^{1 2} Identifying causative genes will lead to enhanced understanding of the disease process and may aid in prevention. Pathologic myopia is associated with molecular changes in the sclera that result in significant scleral thinning, altered scleral architecture, and ocular axial elongation. ³ The sclera is composed of approximately 85% to 90% collagen, with type I collagen the most prevalent. ⁴ Collagen involvement in myopia development by scleral extracellular matrix remodeling leading to ocular elongation has been well characterized. ⁵ Studies of human donor and tree shrew eyes have shown that 19 subtypes of collagen are expressed in the sclera. ^{6 7}  

Mutations in the collagen type I (COL1A1) gene have been reported in clinical conditions associated with myopia, such as type I osteogenesis imperfecta, the Ehlers-Danlos and Marfan syndromes, and osteoporosis. ⁸ The cytogenetic location of the COL1A1 gene is adjacent to a previously identified locus for myopia (MYP5, OMIM 608474; Online Mendelian Inheritance in Man; http://www.ncbi.nlm.nih.gov/Omim/ provided in the public domain by the National Center for Biotechnology Information, Bethesda, MD) on 17q. ⁹ An association of COL1A1 polymorphisms with high-grade myopia was found in a Japanese case–control cohort, ¹⁰ but was not seen in another independent Japanese case–control cohort ¹¹ and a Taiwanese case–control cohort. ¹²  

Collagen type-II (COL2A1) mutations are associated with Stickler syndrome, a condition that has severe myopia as a consistent phenotype. ^{13 14 15} To date, no myopia studies have determined linkage to the COL2A1 locus. A family-based association study of COL2A1 polymorphisms in a Hong Kong Chinese population did not reveal any association with myopia (Tang W, et al. IOVS 2004;45:ARVO E-Abstract 3724). However, a recent association analysis in a predominantly Caucasian family-based dataset suggested involvement of COL2A1 in common, low degrees of myopia. ¹⁶  

Myopia is a common, complex, and multifactorial disorder. The likelihood that multiple genes and environmental factors influence myopia development warrants determination or replication of potential candidate gene involvement in independent and/or diverse datasets. Hence, we investigated the association of COL1A1 and COL2A1 polymorphisms with myopia in two independent, large, Caucasian multiplex high-grade myopia family datasets. Evidence of suggestive linkage to the COL2A1 locus on chromosome 12 from a subset analysis of a genome-wide linkage scan is also presented. 

Materials and Methods

Subject Selection

Informed consent was obtained from all participants. The protocol complied with the principles of the Declaration of Helsinki and received the approval of local ethics committees and institutional review boards. All subjects underwent a complete ophthalmic examination, and individuals with syndromic disorders and systemic conditions that could predispose to myopia were excluded from participation. Two large family-based datasets from Duke University and Cardiff University participated in the association study. The Duke dataset comprised 146 multiplex families with 649 total subjects, and both COL1A1 and COL2A1 polymorphisms were tested. The Cardiff dataset comprised 130 families with 582 individuals and served as an independent study of COL2A1 gene association. In a parallel study in our research program, a total of 254 families from five international centers including the above 146 Duke families (total 1457 subjects) participated in a genome-wide single nucleotide polymorphism (SNP) scan for linkage analyses. ¹⁷  

Marker Selection and Genotyping

The SNPSelector program ¹⁸ was used to select tagging SNPs that met the following two criteria: (1) a squared Pearson correlation (r ²) of at least 0.67 in the linkage disequilibrium (LD) bins; and (2) a minor allele frequency of at least 5% in a Caucasian population. For COL1A1, eight SNPs were chosen and included the SNPs that showed significant association with high myopia identified by Inamori et al. ¹⁰ For COL2A1, 14 SNPs were selected, and included the SNP marker of significance reported by Mutti et al. ¹⁶ A diagram of positions of the selected SNPs relative to the COL1A1 and COL2A1 genes is presented in Figure 1 . To screen the region downstream of the COL2A1 gene, we selected13 additional markers based on LD structure in Caucasians, covering 50 kb (rs12305182, rs4760612, rs2408954, rs10492082, HCV2626586, rs10492081, rs989144, rs12301562, rs4760619, rs757556, rs11168411, rs10875746, and rs11168421). 

For the Duke dataset, total genomic DNA was extracted from venous blood collected from patients (AutoPure LS DNA Extractor and Puregene reagents; Gentra Systems Inc., Minneapolis, MN). Custom allelic discrimination assays (TaqMan; Applied Biosystems, Inc. [ABI], Foster City, CA) consisting of a mixture of unlabeled polymerase chain reaction (PCR) primers and the minor groove binding group (MGB; TaqMan; ABI) probe (FAM and VIC dye-labeled; ABI) were used. Each assay comprised two unlabeled PCR primers and two allele-specific probes. PCR reactions were performed with PCR master mix and genetic analyzers (Taqman Universal PCR Master Mix on the GeneAmp PCR System 9700 and the 7900HT Fast PCR System; ABI) were used for reading allelic discrimination calls. CEPH (Centre d’Etude du Polymorphisme Humain, Paris, France) DNA standards and known duplicate DNA samples were included for quality control. A threshold of 95% genotyping efficiency was required for submission to the analysis database. For the Cardiff replication dataset, DNA was extracted from saline mouthwashes, as previously reported ¹⁹ and genotyping was performed by KBiosciences, Ltd. (Herts, UK), on three COL2A1 SNPs (rs1034762, rs1635529, and rs1793933). 

Statistical Analyses

All markers were tested for Hardy-Weinberg equilibrium (HWE) with the Genetic Data Analysis (GDA) program. ²⁰ LD between markers was computed for all pairs with the Graphical Overview of Linkage Disequilibrium (GOLD) program. ²¹ For association analyses, the family-based pedigree disequilibrium test (PDT) and the association in the presence of linkage (APL) test were used to determine the association of the markers with myopia. ^{22 23 24} The dataset was classified into groups based on the degree of myopia for both spherical (SPH) and spherical equivalent (SE) values. The high-grade myopia group was defined as ≤−5.00 D, the mild-to-moderate myopia group, between −0.50 D and −5.00 D, and the any-myopia group, ≤ −0.50 D. Analyses were also performed with the threshold set at ≤−9.25 D for COL1A1 to mirror the phenotypic threshold criterion established by Inamori et al., ¹⁰ and at ≤−0.75 D for COL2A1 to simulate threshold in Mutti et al. ¹⁶  

The number of affected and unaffected subjects for each classification in Duke and Cardiff datasets is described in detail in Tables 1and 2 , respectively. The dataset was stratified to investigate the effect of genetic background on lower degrees of myopia within this cohort. Approximately 83% of the Duke and 98% of the Cardiff cohorts were over age 20 (an age by which refractive state becomes stable).The clinical information regarding age, sex, and refractive error for various groups in both the datasets is provided in Supplementary Tables S1 and S2. For multiple testing correction, we obtained q-values for all markers by using the Q-Value program (http://faculty.washington.edu/jstorey/qvalue/; provided in the public domain by the University of Washington, Seattle).²⁵Markers were declared to be significantly associated at q < 20%. 

To examine whether any linkage signal existed in the COL2A1 region, linkage analysis on a set of SNPs in the COL2A1 gene and its nearby region (57.69–70.80 cM) was performed. In addition to the SNPs from the association study, the SNPs from the linkage study by Li et al. ¹⁷ within the COL2A1 region were used in the analysis. The dataset in the linkage study was also predominantly Caucasian (91.2%) with Asian- and African-American families contributing 4.8% and 5%, respectively. High myopia was defined as −5.00 D or more, and analyses for the overall dataset and Caucasian subgroup were performed for both the SPH and SE phenotypes. The Merlin program was used to perform parametric multipoint (http://www.sph.umich.edu/statgen/abecasis/Merlin/ provided in the public domain by the Center for Statistical Genetics, School of Public Health, University of Michigan, Ann Arbor) and nonparametric (two-point and multipoint) linkage analyses. ²⁶ Affected-only, two-point linkage analysis was performed with the FastLink program (http://linkage.rockefeller.edu/ provided in the public domain by Rockefeller University, New York, NY) assuming autosomal dominant inheritance. HLOD (heterogeneity logarithm of odds) scores for each marker were generated. 

Results

Association Analyses

All results are presented for the SE phenotype only. The SPH analyses were generally in agreement and not substantially different from the SE analyses. For the COL1A1 gene, there was no significant association of any of the eight markers with the myopia affection status. This lack of association was consistent for all thresholds set for defining myopia and across all the association tests performed. Figure 2depicts the results of APL and PDT analyses for COL1A1 markers. For the moderate myopia group, rs2586486 showed moderate significance (P = 0.03) with spherical data in the APL analysis. Other tests did not support this finding and, when corrected for multiple testing, there was no significant association. The SNP rs1800211 showed moderate significant values in the any-myopia and −9.25 D groups with the APL test; however, the PDT analysis did not support this finding. The SNP rs1061237 showed moderate significance in the −9.25 D group with the APL analysis but was not significant after correcting for multiple testing. 

For the COL2A1 gene, both PDT and APL analyses identified significant association between five SNPs (rs1034762, rs1635529, rs1793933, rs3803183, and rs17122571) of the COL2A1 locus and high-grade myopia status with P < 0.045 (min P = 0.008) in the Duke dataset (Fig. 3) . Analysis of the COL2A1 SNPs with the mild-to-moderate myopia group revealed no significant association, with the exception of the marker rs17122571, but this was not significant after correcting for multiple testing. However, analysis with myopia status set at ≤−0.50 D or ≤−0.75 D (mild, moderate, and high-grade myopia groups combined) revealed significant association of the same five SNPs (min P = 0.004). The APL and PDT analyses results for COL2A1 polymorphisms for the Duke dataset are depicted in Figure 3along with the 13 markers that covered the 50-kb region downstream of COL2A1. The SNP rs1635529 also showed significant association in the Cardiff dataset in high-grade myopia and any-myopia groups (≤−5.00 D, min P = 0.004; ≤−0.50 D and −0.75 D, min P = 0.007). The APL and PDT results for markers tested in the Cardiff dataset are shown in Table 3based on each criterion tested. The positive association of all significant COL2A1 markers was confirmed after correcting for multiple testing (Q-Value program). 

Linkage Analyses

Figure 4shows the linkage results for chromosome 12 from a recent study by Li et al. ¹⁷ A 36.59-cM region on chromosome 12 (89.57–126.16 cM, 12q21.2-22) with a peak marker at rs337663 (HLOD = 3.48, 101.97 cM) was found to have significant linkage using the SPH phenotype. This region included four markers (rs2063239, rs20508, rs1849929, and rs4213) with two-point HLOD scores ≥2. In addition, the nonparametric multipoint analysis of the initial genome-wide linkage scan revealed suggestive linkage peaks that encompassed 53.89 to 57.69 cM (peak marker at rs956066, 12q12, 56.41 cM, HLOD = 1.35) and 70.8 to 74.32 cM (peak marker at rs1504464, 12q14.1, 73.95 cM, HLOD = 1.22; Fig. 4 ). The COL2A1 gene maps to 12q13.11 (62.5 cM) and lies between these two suggestive linkage peaks. After the inclusion of COL2A1 SNPs (genotyped in the association phase) in this region (57.69–70.80 cM), analysis revealed HLOD scores (>1.5) for the COL2A1 locus indicating suggestive linkage. The two-point nonparametric analysis revealed suggestive HLOD scores of 1.69 for marker rs855272 (62.14 cM) and 1.52 for marker rs894734 (69.11 cM; Table 4 ). The multipoint nonparametric analysis revealed several suggestive HLOD scores for the entire region tested between 60.07 and 70.80 cM (peak HLOD = 2.14 at rs1793949, 62.49 cM; Table 5 ). The parametric analyses assuming autosomal dominant inheritance on the COL2A1 locus also revealed similar suggestive HLOD scores (data not shown). The COL1A1 locus did not show linkage to any myopia disease state in this cohort. 

Discussion

Ocular axial elongation in myopia is facilitated by collagen remodeling in the sclera during the development of myopia. We investigated the potential association of the collagen genes COL1A1 and COL2A1 with predisposition to myopia. In large Caucasian family-based cohorts, we examined this relationship by using a complementary genetic association and linkage analyses. We report that COL2A1 alleles are associated with and linked to high-grade myopia in Caucasians. 

The high-grade myopia and any-myopia groups showed significant association with COL2A1 polymorphisms in the two independent family datasets tested, whereas the mild-to-moderate myopia group was not associated, thus indicating major contribution from the high-grade myopia group. The lack of association in the mild-to-moderate myopia group indicates that COL2A1 may not have an effect on lower degrees of myopia in this cohort. The results of this study are consistent with the COL2A1 association with myopia reported by Mutti et al. ¹⁶ in a predominantly Caucasian family-based cohort. It is notable that their analyses were not stratified based on the severity of myopia and therefore reflects the outcome of the any-myopia groups examined in our study. Since association analyses do not necessarily identify the causative gene, based on the linkage disequilibrium structure in Caucasians, further analysis of a 50-kb region downstream of the COL2A1 gene was performed. The analysis did not reveal a stronger association signal than what was observed with the COL2A1 gene polymorphisms. The overall linkage analyses on chromosome 12 from Li et al., ¹⁷ in addition to the replication of the previously reported MYP3 locus, ⁹ revealed suggestive LOD scores near the COL2A1 locus. Substantiating this finding, the subset analysis involving the markers in the COL2A1 locus also revealed significant linkage. Taken together, our findings suggest that the COL2A1 gene could be involved in susceptibility to high-grade myopia in Caucasians. In a recent genome-wide scan performed in dizygotic twin pairs in a U.K. cohort, ²⁷ the COL2A1 locus did not show positive linkage, further supporting the idea of involvement of multiple genes in the development of myopia. 

As described earlier, mutations in the COL2A1 gene have been associated with Stickler syndrome, ^{12 13 14} a condition associated with severe myopia. Furthermore, COL2A1 mutations have also been reported in autosomal dominant rhegmatogenous retinal detachment (RRD), ²⁸ a phenotype that is clinically different from Stickler syndrome and is associated with high-grade myopia. It is interesting to note that high-grade myopia associated with the RRD phenotype is due to ocular elongation without the vitreous body abnormalities generally seen in Stickler syndrome. It is not clear how the COL2A1 gene plays a role in the development of myopia; however, the expression data of COL2A1 in relevant ocular tissues suggest that it could be a potential candidate for future studies on myopia. The COL2A1 gene is expressed in the sclera, ^{7 29 30} the combined retinal pigment epithelium and choroid ^{29 31} and the retina. ²⁸  

The finding that the COL1A1 gene polymorphisms were not associated with myopia is surprising, given that the sclera is predominantly composed of type-I collagen. However, it is possible that COL1A1 may not be associated with myopia in these Caucasian datasets indicating heterogeneity in disease development across different ethnicities. A recent study reported the absence of COL1A1 involvement in a Taiwanese cohort. ¹² More recently, a study on Japanese population failed to replicate the association of COL1A1 gene polymorphisms (that was previously reported by Inamori et al. ¹⁰ ) in an independent dataset. ¹¹ Another reason for the lack of detection of COL1A1 association could be because of overriding effects of other genes involved in myopia development in our cohorts. 

In conclusion, we report genetic association along with suggestive linkage to the COL2A1 locus for nonsyndromic, high-grade myopia in ethnically homogenous, family-based cohorts. The involvement of COL2A1 sequence variants in myopia causation has only been coupled with syndromic disorders in the past. It is important that this locus be investigated in other cohorts with nonsyndromic, high-grade myopia. 

 Supported by National Institutes of Health Grant EY014685 (TLY) and Research To Prevent Blindness Inc.

 Submitted for publication December 22, 2008; revised March 5, 2009; accepted June 12, 2009.

 Disclosure: R. Metlapally, None; Y.-J. Li, None; K.-N. Tran-Viet, None; D. Abbott, None; G.R. Czaja, None; F. Malecaze, None; P. Calvas, None; D. Mackey, None; T. Rosenberg, None; S. Paget, None; T. Zayats, None; M.J. Owen, None; J.A. Guggenheim, None; T.L. Young, None

 The publication costs of this article were defrayed in part by page charge payment. This article must therefore be marked “advertisement” in accordance with 18 U.S.C. §1734 solely to indicate this fact.

 

Figure 1.

 

Schematic representation of the SNPs selected for the COL1A1 and COL2A1 genes (source, Human Genome Browser, http://genome.ucsc.edu/ provided in the public domain by UCSC Genome Bioinformatics, University of California at Santa Cruz, Santa Cruz, CA). A total of 8 SNPs were selected for COL1A1 and 14 SNPs for COL2A1. **SNPs associated with high myopia and reported by Inamori et al. ¹⁰ for COL1A1 and Mutti et al. ¹⁶ for COL2A1.

Table 1.

 

Descriptive Statistics of the Number of Affected and Unaffected Individuals in Each Group for the Association Analyses: Duke Dataset

Group	Definition Based on Myopia Severity	Affected (A)	Unaffected (N)	Unknown (U)	Total
High-grade myopia	SE data: A ≤ −5.00 D, N ≥ −0.49 D, U others	285	155	209	649
Mild to moderate myopia	SE data:−4.99 D ≤ A ≤ −0.50 D, N ≥ −0.49 D, U others	204	155	290	649
Any myopia	SE data: A ≤ −0.50 D, N ≥ 0 D, −0.50 D < U < 0 D	489	131	29	649
−0.75 D (Threshold used in Mutti et al. 16 )	SE data: A ≤ −0.75 D, N ≥ 0 D, −0.75 D < U < 0 D	476	131	42	649
−9.25 D (Threshold used in Inamori et al. 10 )	SE data: A ≤ −9.25 D, N ≥ −0.49 D, U others	126	155	368	649

 Classification of the dataset was based on myopia severity using spherical equivalent refractive data. D, diopters; SE, spherical equivalent refractive data; A, affected; N, unaffected, U, unknown.

Table 2.

 

Descriptive Statistics of the Number of Affected and Unaffected Individuals in Each Group for the Association Analyses: Cardiff Dataset

Group	Definition Based on Myopia Severity	Affected (A)	Unaffected (N)	Unknown (U)	Total
High-grade myopia	SE data: A ≤ −5.00 D, N ≥ −0.49 D, U others	327	56	199	582
Mild to moderate myopia	SE data:−4.99 D ≤ A ≤ −0.50 D, N ≥ −0.49 D, U others	130	56	396	582
Any myopia	SE data: A ≤ −0.50 D, N ≥ 0 D, −0.50 D < U < 0 D	457	44	81	582
−0.75 D (Threshold used in Mutti et al. 16 )	SE data: A ≤ −0.75 D, N ≥ 0 D, −0.75 D < U < 0 D	448	44	90	582

 Classification of the dataset was based on myopia severity using spherical equivalent refractive data. D, diopters; SE, spherical equivalent refractive data; A, affected; N, unaffected; U, unknown.

Figure 2.

 

APL and PDT analyses of the COL1A1 gene-tagging polymorphisms. Analyses were performed for high, moderate, and any-myopia states (SE data presented). The threshold used by Inamori et al. ¹⁰ (−9.25 D) was also considered for analysis.

Figure 3.

 

APL and PDT analyses of the COL2A1 gene-tagging polymorphisms. Analyses were performed for high, moderate, and any-myopia states (SE analyses and significant SNPs presented). The threshold used by Mutti et al. ¹⁶ (−0.75 D) was also considered for analysis. A 50-kb region downstream of COL2A1 was also screened.

Table 3.

 

Association Analyses of the COL2A3 Gene Polymorphisms: Cardiff Dataset

Marker	High-Grade Myopia SE			Mild to Moderate Myopia SE			Any Myopia SE			−0.75 D SE
		APL	PDT	APL	PDT	APL	PDT	APL	PDT
rs1034762	0.1516	0.0629	0.6597	0.4795	0.1314	0.1221	0.1529	0.1221
rs1635529	0.0242	0.0044	0.6803	0.7389	0.0154	0.0073	0.0165	0.0073
rs1793933	0.1471	0.1175	0.3584	0.7815	0.1121	0.1118	0.1054	0.1118

 Analyses were performed for high, moderate, and any myopia states. The threshold used by Mutti et al. ¹⁶ (−0.75 D) was also considered for analysis. All probabilities are uncorrected; significant associations are in bold.

Figure 4.

 

Linkage analysis results for chromosome 12 from the whole-genome linkage scan (Li et al. ¹⁷ ). The MERLIN program was used to perform both two-point and multipoint parametric and nonparametric linkage analyses. Graph depicts the results from parametric analyses using a dominant model, and nonparametric linkage analyses for the overall dataset for chromosome 12.

Table 4.

 

Two-point Linkage Analysis of SNPs in the COL2A1 Gene and the Surrounding Region

Marker	Map Location (cM)	HLOD (SE)	Marker	Map Location (cM)	HLOD (SE)
RS2061192	57.691833	0.83	RS12305182	62.54154	0.00
RS871880	58.311269	0.00	RS4760612	62.541973	0.67
RS1224438	59.410607	0.49	RS2408954	62.542583	0.47
RS965125	59.636525	1.08	RS10492082	62.546254	0.68
RS1012642	60.076303	0.3	RS1978161	62.586208	0.87
RS1444588	60.153754	0.09	HCV2626586	62.587106	0.26
RS1492891	60.234269	0.73	RS10492081	62.593087	0.68
RS739856	62.104263	1.26	RS989144	62.601883	0.18
RS855272	62.148323	1.69	RS12301562	62.602503	0.02
RS1793949	62.493497	0.81	RS4760619	62.617274	0.03
RS1635553	62.497329	1.09	RS757556	62.619745	0.00
RS2276456	62.497722	1.12	RS11168411	62.622166	0.26
RS3829736	62.498231	0.57	RS10875746	62.634956	0.11
RS1635550	62.499646	−0.02	RS11168421	62.635022	0.08
RS1793923	62.505579	0.89	RS1565933	63.061015	0.27
RS12423250	62.51052	0.15	RS296736	63.821215	0.50
RS1034762	62.510904	0.00	RS7532	63.944748	0.87
RS3737548	62.512614	0.48	RS868884	64.570001	0.50
RS954326	62.5159	0.39	RS2641530	65.759645	0.04
RS1635529	62.516169	0.00	RS644524	66.926797	0.11
RS1793933	62.517469	0.00	RS894734	69.10619	1.52
RS3803183	62.519041	−0.01	RS2279400	69.473882	0.00
RS17122571	62.54118	0.00	RS3935215	70.80392	0.62

 SNPs within the COL2A1 locus from the association study and the whole-genome linkage scan were combined for this analysis. LOD scores > 1.5 are in bold italic.

Table 5.

 

Multipoint Linkage Analysis of SNPs in the COL2A1 Gene and the Surrounding Region

SNP	Map Location (cM)	HLOD (SE)
RS2061192	57.69183	1.27
RS871880	58.31127	1.24
RS1224438	59.41061	1.18
RS965125	59.63653	1.18
RS1012642	60.0763	1.31
RS1444588	60.15375	1.33
RS1492891	60.23427	1.38
RS739856	62.10426	1.82
RS855272	62.14832	1.82
RS1793949	62.4935	2.14
RS4760612	62.54197	2.11
RS1565933	63.06102	1.79
RS296736	63.82122	1.69
RS7532	63.94475	1.69
RS868884	64.57	1.62
RS2641530	65.75965	1.74
RS644524	66.9268	1.99
RS894734	69.10619	1.87
RS2279400	69.47388	1.70
RS3935215	70.80392	1.82

 SNPs within the COL2A1 locus from the association study and the whole genome linkage scan were combined for this analysis. LOD scores > 1.5 are in bold italic.

Supplementary Materials

Supplementary Table S1 - (PDF) 

Supplementary Table S2 - (PDF) 

The authors thank all subjects who participated and Anuradha Bulusu, Tristan White, Bei Zhao, and Gary Lipton for assistance with the analyses.