Disease Associations and Family‐Based Tests

Overview of Admixture Mapping

Admixture mapping is a powerful method of gene mapping for diseases or traits that show differential risk by ancestry. Admixture mapping has been applied most often to Americans who trace ancestry to various combinations of Native Americans, Europeans, and West Africans. Recent developments in admixture mapping include improvements in the methods and reference data needed to make inferences about ancestry as well as extensions of the mapping approach in the framework of linear mixed models. This overview outlines the key concepts of admixture mapping. It describes approaches for inferring local ancestry and provides strategies for performing admixture mapping depending on the study design. Finally, linkage analysis, association analysis, and admixture mapping are compared, with an emphasis on integrating admixture mapping and association testing. Published 2023. This article is a U.S. Government work and is in the public domain in the USA.

Pedigree Selection and Information Content

In this article, we discuss strategies for selection of families and family members for genetic studies. We will evaluate strategies to sample large families with multiply affected members, sibships, and nuclear families. In addition, we have added a section to discuss sub-sampling within pedigrees for large sequencing studies, particularly when genome-wide SNP chips are available on all members of a pedigree. The type of family sampled for a study will determine the statistical analyses and power of discovery of genetic findings. We will evaluate study designs that maximize power and allow for linkage and association analyses to identify genetic loci predisposing to phenotype. © 2018 by John Wiley & Sons, Inc.

Statistical methods for genome-wide and sequencing association studies of complex traits in related samples

Genome-wide association studies (GWAS) and sequencing studies are routinely conducted for the identification of genetic variants that are associated with complex traits. Many genetic studies for association mapping include related individuals. When relatives are included in an association analysis, familial correlations must be appropriately taken into account to ensure correct type I error and to increase power. This unit provides an overview of statistical methods that are available for GWAS and sequencing association studies of complex traits in samples with related individuals.

Family-based association study in Tunisian familial psoriasis

BACKGROUND

The pathogenesis of all forms of psoriasis remains obscure. Segregation analysis and twin studies together with ethnic differences in disease frequency all point to an underlying genetic susceptibility to psoriasis, which is both complex and likely to reflect the action of a number of genes.

MATERIALS AND METHODS

In the present study, we performed a family-based association study, and a transmission dysequilibrium test using the PLINK program, in a set of seven Tunisian multiplex families using a panel of 96 single-nucleotide polymorphisms localized in several regions across the genome. Ninety-five of them were reported to be associated with psoriasis in different populations.

RESULTS

Besides the confirmation of association between previous associated regions: 6p, 1p, 2p, 13q, 14q, and 20p, and cutaneous psoriasis, we identified a new association with the rs1249564 in the IL17RD gene.

CONCLUSION

Our results support the complex genetic basis of psoriasis.