Comparison of identical single nucleotide polymorphisms genotyped by the GeneChip Targeted Genotyping 25K, Affymetrix 500K and Illumina 550K platforms.

Comparisons of targeted genotyping chips to ready-made chips are important because targeted chips are suitable for fine-scale association mapping with a reasonable cost. Genotypes produced by the Affymetrix Targeted Genotyping (TG) 25K, Affymetrix 500K, and Illumina 550K arrays for regions on chromosomes 2 and 7 of 90 individuals were assessed to investigate genotype accordance between the platforms. The common SNPs in TG the Affymetrix and Illumina arrays showed similar genotype accordance. The consistency rate of the Illumina array to consensus genotypes, i.e., identically called by more than two platforms, was the highest, and that of the Affymetrix array was the lowest. The TG array data showed high accordance and reasonable consistency between platforms.

SNP linkage analysis and whole exome sequencing identify a novel POU4F3 mutation in autosomal dominant late-onset nonsyndromic hearing loss (DFNA15).

Autosomal dominant non-syndromic hearing loss (AD-NSHL) is one of the most common genetic diseases in human and is well-known for the considerable genetic heterogeneity. In this study, we utilized whole exome sequencing (WES) and linkage analysis for direct genetic diagnosis in AD-NSHL. The Korean family had typical AD-NSHL running over 6 generations. Linkage analysis was performed by using genome-wide single nucleotide polymorphism (SNP) chip and pinpointed a genomic region on 5q31 with a significant linkage signal. Sequential filtering of variants obtained from WES, application of the linkage region, bioinformatic analyses, and Sanger sequencing validation identified a novel missense mutation Arg326Lys (c.977G>A) in the POU homeodomain of the POU4F3 gene as the candidate disease-causing mutation in the family. POU4F3 is a known disease gene causing AD-HSLH (DFNA15) described in 5 unrelated families until now each with a unique mutation. Arg326Lys was the first missense mutation affecting the 3(rd) alpha helix of the POU homeodomain harboring a bipartite nuclear localization signal sequence. The phenotype findings in our family further supported previously noted intrafamilial and interfamilial variability of DFNA15. This study demonstrated that WES in combination with linkage analysis utilizing bi-allelic SNP markers successfully identified the disease locus and causative mutation in AD-NSHL.

Distinct linkage disequilibrium (LD) runs of single nucleotide polymorphisms and microsatellite markers; implications for use of mixed marker haplotypes in LD-based mapping.

It has been suggested that the haplotypic relationship between microsatellite markers and single nucleotide polymorphisms (SNPs) is of considerable importance, as microsatellite markers can potentially be incorporated into haplotypes containing SNPs to increase marker density across a region of interest. However, SNPs and microsatellite markers have different mutation rates and durations, and it is conceivable that the linkage disequilibrium (LD) patterns between the genetic markers may considerably differ. We assessed the LD patterns using 1,661 SNPs and 65 microsatellite markers along chromosome 22 and investigated whether common patterns of LD between the two genetic markers are deduced from the results. The results demonstrated that the patterns of LD among microsatellite markers varied considerably and the LD runs of SNPs and microsatellite markers showed distinct patterns. Microsatellite markers have a much higher mutation rate and the evolution of microsatellite markers is a more complex process which has distinct mutation properties from those of SNPs. We consider that these might contribute to the different LD patterns between the two genetic markers. Therefore, it would seem inadvisable to make assumptions about persistence of LD across even a relatively small genetic distance among microsatellite markers and to construct mixed marker haplotypes/LD maps employing microsatellite markers.