Detection of inappropriate samples in association studies by an IBS-based method considering linkage disequilibrium between genetic markers.

An association study is a popular study design to identify susceptibility genes for common complex diseases. In such a study, the presence of inappropriate samples, such as those derived from close relatives or showing DNA contamination, causes an inflation of type I error or a decrease of power. Here we propose an identity-by-state (IBS)-based detection method of inappropriate samples taking linkage disequilibrium (LD) into consideration. The test statistics is the mean of the proportion of alleles that are shared identical by state at each single nucleotide polymorphism (SNP) between each sample pair in an association study. A covariance of the number of shared alleles between two SNPs is introduced to consider LD. We show that type I error and power are estimated accurately in computer-simulated data, and that if the number of SNPs analyzed is small, the performance of detection of inappropriate samples is superior to the previous method in simulated LD. An application to real association study data showed that accuracy in estimating the distribution of test statistics improved if LD was considered. Sample pairs considered to be siblings were detected. These results suggested that an LD-considered IBS-based detection method is useful in identifying inappropriate samples in an association study.

Sox9 directly promotes Bapx1 gene expression to repress Runx2 in chondrocytes.

The transcription factor, Sry-related High Mobility Group (HMG) box containing gene 9 (Sox9), plays a critical role in cartilage development by initiating chondrogenesis and preventing the subsequent maturation process called chondrocyte hypertrophy. This suppression mechanism by Sox9 on late-stage chondrogenesis partially results from the inhibition of Runt-related transcription factor 2 (Runx2), the main activator of hypertrophic chondrocyte differentiation. However, the precise mechanism by which Sox9 regulates late chondrogenesis is poorly understood. In the present study, the transcriptional repressor vertebrate homolog of Drosophila bagpipe (Bapx1) was found to be a direct target of Sox9 for repression of Runx2 expression in chondrocytes. We identified a critical Sox9 responsive region in the Bapx1 promoter via a luciferase reporter assay. Analysis by chromatin immunoprecipitation and electrophoretic mobility shift assays indicated that Sox9 physically bound to this region of the Bapx1 promoter. Consistent with the notion that Bapx1 and Sox9 act as negative regulators of chondrocyte hypertrophy by regulating Runx2 expression, transient knockdown of Sox9 or Bapx1 expression by shRNA in chondrocytes increased Runx2 expression, as well as expression of the late chondrogenesis marker, Col10a1. Furthermore, while over-expression of Sox9 decreased Runx2 and Col10a1 expressions, simultaneous transient knockdown of Bapx1 diminished that Sox9 over-expressing effect. Our findings reveal that the molecular pathway modulated by Bapx1 links two major regulators in chondrogenesis, Sox9 and Runx2, to coordinate skeletal formation.