Meta-analysis Of Linkage Studies Research Articles

Meta-Analysis of Genome-Wide Linkage Studies in Celiac Disease

Objective: A meta-analysis of genome-wide linkage studies allows us to summarize the extensive information available from family-based studies, as the field moves into genome-wide association studies. Methods: Here we apply the genome scan meta-analysis (GSMA) method, a rank-based, model-free approach, to combine results across eight independent genome-wide linkages performed on celiac disease (CD), including 554 families with over 1,500 affected individuals. We also investigate the agreement between signals we identified from this meta-analysis of linkage studies and those identified from genome-wide association analysis using a hypergeometric distribution. Results: Not surprisingly, the most significant result was obtained in the HLA region. Outside the HLA region, suggestive evidence for linkage was obtained at the telomeric region of chromosome 10 (10q26.12-qter; p = 0.00366), and on chromosome 8 (8q22.2-q24.21; p = 0.00491). Testing signals of association and linkage within bins showed no significant evidence for co-localization of results. Conclusion: This meta-analysis allowed us to pool the results from available genome-wide linkage studies and to identify novel regions potentially harboring predisposing genetic variation contributing to CD. This study also shows that linkage and association studies may identify different types of disease-predisposing variants.

Mapping a gene for rheumatoid arthritis on chromosome 18q21

Although single chi-square analysis of the North American Rheumatoid Arthritis Consortium (NARAC) data identifies many single-nucleotide polymorphisms (SNPs) with p-values less than 0.05, none remain significant after Bonferroni correction. In contrast, CHROMSCAN evades heavy Bonferroni correction and auto-correlation between SNPs by using composite likelihood to model association across all markers in a region and permutation to assess significance. Analysis by CHROMSCAN identifies a 36-kb interval that includes the most significant SNP (msSNP) observed in a 10-Mb target suggested by linkage. Unexpectedly, stratification by gender and age of onset shows that association evidence comes almost entirely from females with age of onset less than 40. Combining evidence from a meta-analysis of linkage studies and three subsets of the NARAC data provides significant evidence for a determinant of rheumatoid arthritis in a 36-kb interval and illustrates the principle that estimates of location and its information are more powerful than estimates of p-values alone.

Haplotypes within genes of β-chemokines in 17q11 are associated with multiple sclerosis: a second phase study

We previously defined haplotypes of single nucleotide polymorphisms (SNP) with possible relevance to multiple sclerosis (MS) in 2 CC chemokine ligand (CCL) clusters in chromosome 17q11. The 17q11 region was also identified as a susceptibility locus by a meta-analysis of linkage studies. To confirm and refine the previous finding in a second, high resolution SNP scan in a new set of families. We genotyped 232 SNPs in 1369 individuals in 361 MS families. Transmission of marker alleles and haplotypes from unaffected parents to affected offspring was tested by using the pedigree disequilibrium test, the TRANSMIT 2.5 program, and the family and haplotype based association tests. Distribution of linkage disequilibrium (LD) was assessed by ldmax. In consensus with observations in the first scan, the present study identified haplotypes within CCL3 and CCL15 in the telomeric CCL cluster. There was also an overlap in the findings in the centromeric CCL cluster. Strong and extensive LD was detected both within the centromeric and telomeric CCL gene clusters. The present study replicates our previous findings and further suggests the existence of MS associated haplotypes within genes of CCL3 and CCL15. Haplotypes of interest are also present within the centromeric gene cluster (including CCL2, CCL7, CCL11, CCL8, and CCL13), but extensive LD prevents further refinement of these haplotypes by using the methods applied. Sequencing of the identified chromosomal segments and their flanking regions will be necessary to define specific variants with direct relevance to MS pathogenesis.

Meta-analysis of linkage studies.

Lander and Kruglyak [1995] gave guidelines for interpreting linkage results based on estimating how often a particular threshold for significance would be exceeded by chance in a single genome scan. What is unknown is how often two or more genome scans would exceed a particular threshold within the same region. We develop theoretical estimates of these values and compare these with the empirical estimates derived from the GAW11 data. For single-point analysis, the theoretical estimates predict the empirical estimates. For multipoint analysis, the theoretical values overestimate what is observed. For both single point and multipoint, modest p-values within a single genome scan may give highly significant results when replicated in the same region in other scans.