Brief Report: Whole-Exome Sequencing for Identification of Potential Causal Variants for Diffuse Cutaneous Systemic Sclerosis.

OBJECTIVE: Scleroderma is a genetically complex autoimmune disease with substantial phenotypic heterogeneity. Previous genome-wide association studies have identified common genetic variants associated with disease risk, but these studies are not designed to capture rare or potential causal variants. Our goal was to identify rare as well as common genetic variants in patients with diffuse cutaneous systemic sclerosis (dcSSc) through whole-exome sequencing (WES) in order to identify potential causal variants. METHODS: We generated WES data for 32 dcSSc patients with or without interstitial lung disease (ILD) and for 17 healthy "in-house" controls. Variants were annotated and filtered by quality, minor allele frequency, and deleterious effects on gene function. We applied a gene burden test to identify novel dcSSc and dcSSc-associated ILD candidate genes that were enriched with deleterious variants in cases compared to in-house controls as well as controls from the 1000 Genomes Project (n = 130). RESULTS: We identified 70 genes that were enriched with deleterious variants in dcSSc patients. Two of them (BANK1 and TERT) were in pathways previously implicated in SSc or ILD pathogenesis or known susceptibility loci. Newly identified genes (COL4A3, COL4A4, COL5A2, COL13A1, and COL22A1) were significantly enriched in the extracellular matrix-related pathway, which is relevant to the fibrotic features of dcSSc, and in the DNA repair pathway (XRCC4). CONCLUSION: This study demonstrates the value of WES for the identification of novel gene variants and pathways that may contribute to scleroderma risk and/or severity. The candidate genes we discovered are potential targets for in-depth functional studies.

Pbx Regulates Patterning of the Cerebral Cortex in Progenitors and Postmitotic Neurons.

We demonstrate using conditional mutagenesis that Pbx1, with and without Pbx2(+/-) sensitization, regulates regional identity and laminar patterning of the developing mouse neocortex in cortical progenitors (Emx1-Cre) and in newly generated neurons (Nex1-Cre). Pbx1/2 mutants have three salient molecular phenotypes of cortical regional and laminar organization: hypoplasia of the frontal cortex, ventral expansion of the dorsomedial cortex, and ventral expansion of Reelin expression in the cortical plate of the frontal cortex, concomitant with an inversion of cortical layering in the rostral cortex. Molecular analyses, including PBX ChIP-seq, provide evidence that PBX promotes frontal cortex identity by repressing genes that promote dorsocaudal fate.

Genome-wide haplotype association mapping in mice identifies a genetic variant in CER1 associated with BMD and fracture in southern Chinese women.

BMD is a heritable trait and risk indicator for osteoporosis. In this study, we used a genome-wide haplotype association mapping (HAM) approach to identify a haplotype block within Cer1 that partitions inbred mice strains into high and low BMD groups. A cohort of 1083 high and low BMD human subjects were studied, and a nonsynonymous SNP (rs3747532) in human CER1 was identified to be associated with increased risk of both low BMD in premenopausal women (OR: 2.2; 95% CI: 1.0-4.6; p < 0.05) and increased risk of vertebral fractures (OR: 1.82, p = 0.025) in the postmenopausal cohort. We also showed that Cer1 is expressed in mouse bone and growth plate by RT-PCR, immunohistochemistry, and in situ hybridization, consistent with polymorphisms potentially influencing BMD. Our successful identification of an association with CER1 in humans together with our mouse study suggests that CER1 may play a role in the development of bone or its metabolism. Our study highlights the use of publicly available databases for rapidly surveying the genome for quantitative trait loci.