Human Molecular Genetics, 2002, Vol. 11, No. 21 2599-2606
© 2002 Oxford University Press
Evidence for an inflammatory bowel disease locus on chromosome 3p26: linkage, transmission/disequilibrium and partitioning of linkage
1Division of Gastroenterology, Hepatology and Nutrition, Department of Medicine, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, 2Department of Human Genetics, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania, 3Department of Gastroenterology, The Cleveland Clinic Foundation, Cleveland, Ohio, 4The Martin Boyer Laboratories, Section of Gastroenterology, Department of Medicine, The University of Chicago Hospitals, Chicago, Illinois, 5Harvey M. and Lyn P. Meyerhoff Inflammatory Bowel Disease Center, Johns Hopkins University School of Medicine, Baltimore, Maryland and 6The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania
Received May 29, 2002; Revised July 17, 2002; Accepted July 27, 2002
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
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Crohn's disease and ulcerative colitis, the two major forms of idiopathic inflammatory bowel disease (IBD), are heritable, complex traits that appear to share some but not all susceptibility loci. We report that transmission/disequilibrium test analysis of a Crohn's disease genome scan dataset has detected an inflammatory bowel disease locus on chromosome 3p26 (nominal P=0.000052 and genome-wide corrected P=0.039 at D3S1297). An allele sharing method shows significant linkage (multipoint lod=3.69) in a larger, independent sample of inflammatory bowel disease-affected sibling pairs. A survey of 16 chromosome 3p26 short tandem repeat polymorphisms in a combined sample of 234 independent nuclear families with 324 IBD-affected sibling pairs shows significant linkage to chromosome 3p26 (multipoint lod=3.78) and significant transmission/disequilibrium test results at two adjacent markers (nominal P values in two different transmission/disequilibrium analysis methods=0.00011 and 0.0011 for the first marker, and 0.00071 and 0.00013 for the second marker). There is highly significant under-transmission of a common allele and modest over-transmission of other alleles at both markers. Families with no transmission to affected individuals of the under-transmitted alleles show significant linkage (multipoint lod=4.50) that is significantly greater in four simulation studies (P=0.0001, 0.0000625, 0.0000625 and 0.0000625, respectively) than the linkage evidence in families with transmission of the under-transmitted alleles (multipoint lod=0.12). Thus, the existence of an inflammatory bowel disease locus on chromosome 3p26 is supported by significant linkage, transmission/disequilibrium and partitioning of linkage evidence.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
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Crohn's disease (CD) and ulcerative colitis (UC) are the major forms of idiopathic inflammatory bowel disease (IBD). CD and UC are heritable with complex genetics (1). Genome scans and other genetic linkage studies in IBD have identified several linkages that satisfy Lander and Kruglyak criteria for confirmed linkage (2), including confirmed linkage between CD and the pericentromeric region of chromosome 16 (the IBD1 locus) (3–12), confirmed linkage between IBD (especially UC) and a locus on chromosome 12q (the IBD2 locus) (8,10,13–17), confirmed linkage between IBD (especially CD) and a locus on chromosome 6p (the IBD3 locus) (10,18–22), confirmed linkage between CD and a locus on chromosome 14q (the IBD4 locus) (16,23–25), and confirmed linkage between IBD and a locus on chromosome 3p (13,21,26–28). Other linkages satisfy Lander and Kruglyak criteria for significant linkage but have not been replicated in independent studies with sufficient evidence to satisfy criteria for confirmed linkage (2). These include significant linkage between CD and a locus on chromosome 5q in families with at least one CD-affected with age at diagnosis
16 (the IBD5 locus) (21), significant linkage between IBD and a locus on chromosome 19p (the IBD6 locus) (21), and significant linkage between IBD and a locus on chromosome 1p (the IBD7 locus) (6,29,30). Three relatively uncommon polymorphisms in the CARD15/NOD2 gene, located within the IBD1 linkage interval, have been independently associated with CD (particularly ileal CD) but not UC (31–36). A common haplotype that spans the chromosome 5q31 cytokine gene cluster, located within the IBD5 locus, has also been associated with CD (37). The CARD15/NOD2 and chromosome 5q31 cytokine gene cluster associations do not fully explain the genetics of CD and have not been associated with UC, so other IBD genes remain to be found (37,38). Allele-sharing, model-free linkage analysis of our CD genome scan dataset showed significant linkage to chromosome 14q11–12, confirming suggestive linkage found in a previously published study and establishing this locus as the IBD4 locus (16,23). No other linkage evidence in our genome scan satisfied the stringent Lander and Kruglyak criteria for suggestive or significant linkage (2,23). The transmission/disquililbrium test (TDT) was introduced as a test for linkage in the presence of population association and it can sometimes detect linkage when allele sharing methods do not (39,40). The TDT has the correct significance level as a test of linkage, even when data from multiple affected individuals per family are considered, although the original TDT does not accurately reflect the significance of linkage disequilibrium independent of linkage under these circumstances. Since our CD genome scan dataset contained a relatively high-density of markers (751 microsatellites, average genetic distance between markers=4.6 cM), we reanalysed our genome scan dataset with the TDT as an alternative test for linkage (23). A significant linkage result by TDT analysis at a chromosome 3p26 marker has led us to further investigate chromosome 3p26 in a larger sample of study subjects.
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RESULTS |
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TOPABSTRACTINTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
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Transmission/disequilibrium test analysis of Crohn's disease genome scan dataset detects linkage to chromosome 3p26
Re-analysis of our previously published genome scan dataset from CD-only families (23) with the TDTLIKE program (41) shows significant departure from random allele transmission to affected individuals with a P value that remains significant after Bonferroni correction at marker D3S1297 on chromosome 3p26 (nominal P=0.000052, genome-wide corrected P=0.039). The D3S1297 data fall within the expected distribution for Hardy–Weinberg equilibrium (data not shown) (42). Most of the distortion of allele transmission is due to over-transmission of allele 4, which has 51 transmissions versus 17 non-transmissions (P=0.00018). The TDTLIKE P values accurately reflect the significance of linkage, but they do not accurately reflect the significance of linkage disequilibrium independent of linkage since we used TDTLIKE to analyze data from related affected individuals and not just independent trios of parents and their affected offspring. The TDT result contrasts with the modest, model-free, multipoint lod score of 0.8 that we observed at D3S1297 in the original allele sharing analysis of our genome scan (23).
Allele-sharing analysis of an independent dataset shows replication of linkage to chromosome 3p26
If the TDT result is due to true linkage between D3S1297 and an IBD locus, then we would expect to observe greater linkage evidence in a larger sample with additional flanking markers genotyped (43). A second, independent study sample consisting of 178 independent Caucasian nuclear families with 230 IBD-affected sibling pairs was genotyped at D3S1297 and two flanking short tandem repeat polymorphisms (STRPs) found in sequence data from bacterial artificial chromosomes (BACs) RP11-717m12 and -762o12. The 178 families included 96 CD-only families with 120 affected sibling pairs, 29 UC-only families with 38 affected sibling pairs and 53 mixed (both CD and UC or indeterminate) IBD families with 72 affected sibling pairs. We found significant linkage (maximal multipoint lod=3.69) when we used the ASPEX sib_phase program (44) to perform allele sharing, model-free linkage analysis of the three-marker dataset from all 178 families in the replication study sample. The affected sibling pairs in the CD-only families, the UC-only families and the mixed IBD families all contributed to the evidence for linkage (maximal multipoint lod scores=1.42 for the 120 affected sibling pairs in the CD-only families, 0.57 for the 38 affected sibling pairs in the UC-only families and 2.10 for the 72 affected sibling pairs in the mixed IBD families). When we used the TDTLIKE program to analyze the replication dataset, we did not find significant departure from random allele transmission to affected individuals in the whole replication dataset or in the CD-only, UC-only or mixed IBD family subsets (data not shown).
The findings of the TDTLIKE analysis of our original genome scan dataset and the replication study are consistent with significant linkage to chromosome 3p26 but not with significant linkage disequilibrium between IBD and D3S1297 or either of the flanking STRPs that we genotyped in the replication study.
Fine mapping shows significant transmission/disequilibrium at two adjacent STRPs
To fine map the chromosome 3p26 IBD locus, we genotyped all independent nuclear families with CD-affected sibling pairs from our CD genome scan study sample, consisting of 56 independent nuclear families with 94 CD-affected sibling pairs, and the 178 independent nuclear families with 230 IBD-affected sibling pairs (96 CD-only families with 120 affected sibling pairs, 29 UC-only families with 38 affected sibling pairs and 53 mixed IBD families with 72 affected sibling pairs) from our second study sample at 16 chromosome 3p26 STRPs shown in Table 1. The fine mapping data for these cohorts were analyzed together since they all contributed to the evidence for a disease locus on chromosome 3p26. The data for all 16 STRPs fall within the expected distribution for Hardy–Weinberg equilibrium (data not shown) (42). Table 2 shows the genetic map, marker characteristics and ASPEX sib_phase single- and multi-point model-free lod scores for the 16 STRPs. There is strong evidence for linkage (maximal multipoint lod=3.78) across the markers that we genotyped in the combined cohort of 234 families with 324 IBD-affected sibling pairs. Table 3 shows the results of single-locus TDT analyses using both the ASPEX sib_tdt and TRANSMIT programs and two-locus TDT analyses using the TRANSMIT program (44,45). The sib_tdt and the TRANSMIT P values reflect the significance of linkage disequilibrium independent of linkage within independent nuclear families (44,45). The adjacent STRPs 13 (D3S3525) and 14 and two-locus haplotypes formed by STRP 13 (D3S3525)-STRP 14 and STRP14-STRP 15, show significant departure from random allele transmission to affected individuals, which suggests that STRP 13 (D3S3525) and STRP 14 are in significant linkage disequilibrium with a chromosome 3p IBD locus.
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Transmission of STRP 13 (D3S3525)-allele 4 or STRP 14-allele 1 partitions the linkage evidence
Table 4 shows the individual allele transmission data for STRP 13 (D3S3525) and STRP 14. There is highly significant under-transmission of STRP 13 (D3S3525)-allele 4 and STRP 14-allele 1 and there is modest over-transmission of other alleles, including STRP 13 (D3S3525)-allele 3, STRP 14-allele 2, and STRP 14-allele 4. We hypothesize that IBD-affected individuals who inherit either of the under-transmitted alleles are phenocopies whose IBD is not due to a chromosome 3p26 IBD locus, but may be due to other IBD loci. We expected that the evidence for linkage would be confined to those families without transmission of the under-transmitted STRP 13 (D3S3525) and STRP 14 alleles. In 114 families, at least one IBD-affected sibling inherited either STRP 13 (D3S3525)-allele 4 or STRP 14-allele 1 and in 120 families, none of the IBD-affected siblings inherited either of the under-transmitted alleles. Transmission of STRP 13 (D3S3525)-allele 4 or STRP 14-allele 1 to IBD-affected offspring is associated with little evidence for linkage (model-free multipoint lod at STRP 13=0.12) and almost all of the linkage evidence comes from those families with no transmission of the under-transmitted alleles to IBD-affected offspring (model-free multipoint lod at STRP 13=4.50). The significance of the observed lod score difference between the two groups of families was assessed using four computer simulation studies. In the first study, the total set of 234 families was randomly split into groups of 114 families and 120 families 10 000 times and multipoint lod scores were computed in the simulated groups of families. The observed multipoint lod score differences at STRP 13 are highly significant, as none of 10 000 replicates have a lod score difference as large as the one that we observed (P=0.0001). Therefore, differences in sampling or in sample sizes do not appear to be sufficient to explain the observed lod score difference. In the second and third simulation studies, a disease locus was simulated on a map of four markers in this region with marker allele frequencies and marker-to-marker linkage disequilibrium values matching those observed. The second simulation study was done under linkage homogeneity and the third simulation study was done under 50% linkage heterogeneity. The simulated data was then partitioned according to whether STRP13 (D3S3525)-allele 4 or STRP 14-allele 1 was transmitted to an IBD-affected offspring and the lod score differences between these partitions were measured. The observed multipoint lod score differences at STRP 13 (D3S3525) are again shown to be highly significant, as none of 16 000 replicates in the second simulation study or the third simulation study have a lod score difference as large as the one that was observed (P=0.0000625 for both the second and third simulation studies), indicating that partitioning of the linkage signal is not biasing us towards large observed lod score differences. In a similar fashion, in the fourth simulation study, genotype data for these four markers was again simulated with marker allele frequencies and marker-to-marker linkage disequilibrium values matching those observed, but in this case the data was simulated without considering the disease phenotypes (i.e., the marker data was not linked to the disease phenotypes). The partitioning according to the under-transmitted alleles was performed and the lod score differences were recorded, and again the observed multipoint lod score differences at STRP 13 (D3S3525) are shown to be highly significant, as none of the 16 000 replicates in the fourth simulation study have a lod score difference as large as the one that was observed (P=0.0000625), indicating that the partitioning of identity-by-descent information is not significantly influencing our observed lod score differences. Taken together, the second, third and fourth simulation studies suggest that the bias in allele sharing between our two groups due to our partitioning scheme is not sufficient to explain the difference in observed lod scores, and therefore, transmission of the STRP 13 (D3S3525) or STRP 14 alleles significantly partitions the linkage evidence (46,47).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
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Our data provide strong support for an IBD locus on chromosome 3p26. We initially detected the chromosome 3p26 locus by using a multiallelic extension of the TDT to analyze our high-density CD genome scan dataset. Allele sharing, model-free linkage analysis showed only modest evidence for linkage to chromosome 3p26 in the initial CD genome scan dataset, but we found significant linkage in a larger, independent sample of IBD-affected sibling pairs and the combined study sample. Finally, we found significant departure from random allele transmission to IBD affected individuals at two adjacent chromosome 3p26 markers in the combined study sample, and we found that transmission of under-transmitted alleles to IBD affected individuals at these marker loci partitions the linkage evidence.
The chromosome 3p26 markers that show linkage, transmission/disequilibrium and partitioning of linkage evidence for a nearby IBD locus are located 
45 cM p-telomeric from markers that define a replicated chromosome 3p21 IBD linkage peak (13,21,26–28). The resolution of allele sharing methods for fine localization of complex trait susceptibility loci is limited (48–51), but the TDT should have greater resolution than allele sharing methods to localize disease loci. The chromosome 3p26 locus that we have detected by both allele sharing methods and the TDT is unlikely to be the same as the chromosome 3p21 IBD locus. Further support for two IBD loci on chromosome 3p comes from a recent fine mapping study at 43 chromosome 3p microsatellites in 268 North European Caucasian families with 353 IBD-affected sibling pairs (27). This European study showed evidence for two distinct linkage peaks on chromosome 3p: (1) a linkage peak with a multipoint lod score=1.65 located 10 cM centromeric from the chromosome 3p26 linkage peak that we have detected (the most p-telomeric marker in the European study was a few cM centromeric from the interval that we studied); and (2) another linkage peak with a multipoint lod score=1.40 that overlaps the chromosome 3p21 linkage interval. It is likely that the first of these two peaks is due to the same IBD locus that we have detected in our study.
Our observations are a practical example of the theoretical greater power of allelic association-based methods compared to linkage analysis methods to detect disease loci with only modest effects (40). We would have overlooked the chromosome 3p26 locus if we had relied only on allele sharing, model-free linkage analysis, and not the TDT, to analyze our genome scan dataset.
We found significant departure from random allele transmission to affected individuals but only modest linkage evidence by an allele sharing method at D3S1297 in our initial CD genome scan dataset, and significant linkage by an allele sharing method but lack of significant departure from random allele transmission to affected individuals at D3S1297 in our second and combined study samples. We speculate that the explanation for these observations may be that D3S1297 is in only weak linkage disequilibrium with the chromosome 3p26 IBD locus in the population and we could no longer detect this weak linkage disequilibrium when we added heterogeneity by studying a larger study sample. However, we did detect significant linkage disequilibrium between IBD and two other markers that are adjacent to each other in the combined study sample, possibly because these markers are closer to an IBD locus than D3S1297. We have embarked on a comprehensive linkage disequilibrium mapping effort in this region to identify the IBD-predisposing genetic variants.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
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Institutional review board approval
We have established IBD family DNA repositories for genetic studies at the University of Pittsburgh, University of Chicago and Johns Hopkins University. The institutional review boards at each institution approved the protocol and informed consent was obtained from all study subjects.
Transmission/disequilibrium test analysis of genome scan dataset
The study subjects and genetic markers in our high-density genome scan in CD-only families have been described in a previous publication (23). The TDTLIKE program (41) was used as an alternative test for linkage to reanalyze our genome scan dataset (23). TDTLIKE implements a multiallelic extension of the original TDT (39,41). Since we used TDTLIKE to analyze all data from our genome scan dataset, including data from related affected individuals and not just independent trios of parents and their affected offspring, the TDTLIKE global P values accurately reflect the significance of linkage, but they do not accurately reflect the significance of linkage disequilibrium independent of linkage. TDTLIKE global P values were corrected for multiple comparisons (they were multiplied by 751, since we tested 751 markers) and corrected global P values <0.05 were considered significant evidence for linkage.
Replication of linkage
We carried out a study to determine whether we could replicate the linkage to chromosome 3p26 that was detected in the TDTLIKE analysis of our genome scan dataset. We studied an independent study sample that consisted of 702 members of 178 independent, Caucasian nuclear families with at least one IBD-affected sibling pair. Eighty-seven families from the University of Pittsburgh repository were supplemented with 46 from the University of Chicago repository and 45 from the Johns Hopkins University repository. The Chicago and Baltimore families were chosen because both parents were available for genotyping and they were the same well-characterized families that the Chicago and Baltimore groups contributed to the IBD International Genetics Consortium study of the IBD1 and IBD2 loci (12). Birthdates and initials of names were compared to ensure that there was no duplication of families. The 178 families in the replication study sample consisted of 96 CD-only families with 120 affected sibling pairs, 29 UC-only families with 38 affected sibling pairs and 53 mixed (both CD and UC or indeterminate) IBD families with 72 affected sibling pairs.
The replication study subjects were genotyped at D3S1297 and two flanking STRP markers found in sequence data from BACs RP11-717m12 and -762o12 (STRPs 6, 10, and 15 in Table 1). The genotyping data were checked for Mendelian inconsistencies using the PedCheck program (52) and for Hardy–Weinberg equilibrium using the HWE program (42). The ASPEX version 2.3 sib_map program was used to obtain multipoint maximum likelihood estimates of the map distances between STRPs from the nuclear family data (44). The ASPEX sib_phase program was used to perform allele-sharing, model-free linkage analysis (44). This program uses all available marker data from a family to calculate likelihoods for linkage analysis. Allele frequencies are used to reconstruct missing parents and parental data is phased across multiple markers. Determination of the most likely parental phase is not done, rather a weighting over all possible sets of haplotypes consistent with the data is done. The TDTLIKE program was also used to analyze the replication dataset (41).
Fine mapping
We studied all independent nuclear families with CD-affected sibling pairs from our CD genome scan study sample, consisting of 56 independent nuclear families with 94 CD-affected sibling pairs and the 178 independent nuclear families with 230 IBD-affected sibling pairs from our replication study sample. The combined study sample consisted of 234 independent nuclear families with 324 IBD-affected sibling pairs. Seventy-nine percent of the parents were available for genotyping and unaffected siblings were included in the study sample whenever possible for families with missing parents.
All individuals in the combined study sample were genotyped at a total of 16 STRP loci in the region of interest (Table 1). The STRP loci included D3S1297 and the two flanking STRPs described above, plus 13 other STRPs found in sequence data from BACs RP11-621c18, -497i24, 717m12, -229e21, -121d3, -762o12 and -63o1. The genotyping data were checked for Mendelian inconsistencies using the PedCheck program (52) and for Hardy–Weinberg equilibrium using the HWE program (42). The 16 STRPs were ordered according to the sequence within Homo sapiens chromosome 3 working draft sequence segment NT_00927.7. The ASPEX sib_map program was used to obtain multipoint maximum likelihood estimates of the map distances between markers from the nuclear family data (44). The ASPEX sib_phase program was used to perform single- and multi-point model-free linkage analyses (44). The ASPEX sib_tdt program was used to test for linkage disequilibrium between IBD and each of the STRPs (44). Sib_tdt calculates empirical probabilities for chi-squared statistics, which accurately reflect linkage disequilibrium independent of linkage within independent nuclear families (44). The TRANSMIT 2.5.2 program was also used to test for linkage disequilibrium between IBD and each STRP and two-locus haplotypes formed by adjacent pairs of STRPs (45). TRANSMIT implements a multi-locus TDT test, as well the standard single-locus test. Like the sib_phase program, TRANSMIT uses the available marker data to reconstruct missing parents and to calculate its likelihoods. Also, like sib_phase, the determination of a most likely parental haplotype is not done, but rather the program statistically weights and combines results from all possible sets of haplotypes which are consistent with the observed data. Data were available for 79% of the parents, reducing the problem of determining parental haplotypes. For the TRANSMIT analyses, haplotypes with frequencies <5% were collapsed and the robust estimator option was used.
Partitioning of linkage
To determine whether transmission of STRP 13 (D3S3525)-allele 4 or STRP 14-allele 1 partitions the linkage evidence, the 234 families were divided into one group of 114 families with transmission of STRP 13-allele 4 or STRP 14-allele 1 to at least one IBD-affected offspring, and another group of 120 families with no transmission of these alleles to any IBD-affected offspring. The ASPEX sib_phase (44) multipoint lod score at STRP 13 (D3S3525) was then computed for each group. To determine the significance of the observed difference in the lod scores between the two groups of families, four computer simulation studies were conducted. These simulations answered two questions: (1) did a difference in sampling or in sample sizes of the two groups have an effect on the observed lod score difference?; (2) did the selection of families based on alleles at STRP 13 (D3S3525) and STRP 14 bias us towards observing such a large lod score difference? To answer the first question, the significance of the observed lod score difference between the two groups was determined by a computer simulation in which the total set of 234 families was randomly split into groups of 114 families and 120 families 10 000 times and the ASPEX sib_phase (44) multipoint lod scores were computed in the simulated groups of families to see how often the observed lod score differences occurred. To answer the second question, three similar simulation studies were performed. Data for STRP 13 (D3S3525) and STRP 14 were combined into haplotypes and the observed haplotype frequencies were calculated. These haplotype frequencies were then used to simulate haplotype data and data at two flanking markers (using their respective observed allele frequencies). The simulated haplotype alleles were then expanded to the corresponding single locus genotypes at STRP 13 (D3S3525) and STRP 14, giving us simulated data which retained the observed degree of linkage disequilibrium between these two loci. This simulated data was then subjected to model-free linkage analysis using ASPEX sib_phase (44). In one simulation study, the simulated data were generated under the assumption of linkage to a locus in the vicinity of STRP 13 (D3S3525), so that the resulting data gave lod scores on the order of the multipoint lod score observed at STRP13 (D3S3525) in our original data (2.5–3). In another simulation, the above procedure was repeated, but under the assumption that 50% of the families were unlinked to the simulated disease locus. In the last simulation, the simulated data were generated without consideration of disease phenotype information. We then subdivided each replicate's data by separating families in which STRP13 (D3S3525)-allele 4 or STRP 14-allele 1 was transmitted to an IBD-affected offspring from those families in which no IBD-affected offspring had these alleles. These simulations were repeated 16 000 times and in each case the difference in lod scores between the two sets of families was recorded.
Genetic markers and genotyping
The 16 STRPs that we studied were amplified by PCR using the fluorescence-labeled forward and unlabeled reverse oligoprimers shown in Table 1. The sequence gtttctt was included on the 5' end of most of the reverse primers to minimize genotyping errors secondary to inconsistent adenylation of the 3' end of the forward strand (53). The fluorescently labeled PCR amplimers were electrophoresed and detected on ABI 377 DNA sequencers (Applied Biosystems, Foster City, CA, USA) and were genotyped with GENESCAN and GENOTYPER (Applied Biosystems) software.
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ACKNOWLEDGEMENTS |
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Genotyping and statistical analyses were funded by a grant to R.H.D. from the Crohn's & Colitis Foundation of America. Study subject recruitment was funded by the Scaife Family Foundation (R.H.D.), NIH/NIDDK R01DK55731 (J.H.C.), the Gastrointestinal Research Foundation (J.H.C.), the Meyerhoff IBD Center (S.R.B. and T.M.B.), the Crohn's & Colitis Foundation of America (S.R.B. and T.M.B.) and NIH/NCRR GCRC RR00052 (S.R.B.).
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FOOTNOTES |
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* To whom correspondence should be addressed at: S724 Biomedical Science Tower, 3500 Terrace Street, Pittsburgh, PA 15261. Tel: 4126481897, Fax: 4123838753; Email: duerr{at}msx.dept-med.pitt.edu
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REFERENCES |
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