Project description:Human genetic variants are classified based on potential pathogenicity to guide clinical decisions. However, mechanistic uncertainties often preclude definitive categorization. Germline coding and enhancer variants within the hematopoietic regulator GATA2 create a bone marrow failure and leukemia predisposition. The conserved murine enhancer promotes hematopoietic stem cell (HSC) genesis, and a single-nucleotide human variant in an Ets motif attenuates chemotherapy-induced hematopoietic regeneration. We describe “conditionally pathogenic” (CP) enhancer motif variants that differentially impact hematopoietic development and regeneration. The Ets motif variant functioned cell-autonomously in hematopoietic cells to disrupt hematopoiesis. Since an epigenetically-silenced normal allele can exacerbate phenotypes of a pathogenic heterozygous variant, we engineered a bone marrow failure model harboring the Ets motif variant and a severe enhancer mutation on the second allele. Despite normal developmental hematopoiesis, regeneration in response to chemotherapy, inflammation, and a therapeutic HSC mobilizer was compromised. The CP paradigm informs mechanisms underlying phenotypic plasticity and clinical genetics.
Project description:Mutations in protein-coding genes are well established as the basis for human cancer, yet how alterations within noncoding genome, a substantial fraction of which contain cis-regulatory elements (CRE), contribute to cancer pathophysiology remains elusive. Here, we developed an integrative approach to systematically identify and characterize noncoding regulatory variants with functional consequences in human hematopoietic malignancies. Combining targeted resequencing of hematopoietic lineage-associated CREs and mutation discovery, we uncovered 1,836 recurrently mutated CREs containing leukemia-associated noncoding variants. By enhanced CRISPR/dCas9-based CRE perturbation screening and functional analyses, we identified 218 variant-associated oncogenic or tumor-suppressive CREs in human leukemia. Noncoding variants at KRAS and PER2 enhancers reside in proximity to nuclear receptor (NR) binding regions and modulate transcriptional activities in response to NR signaling in leukemia cells. NR binding sites frequently colocalize with noncoding variants across cancer types. Hence, recurrent noncoding variants connect enhancer dysregulation with nuclear receptor signaling in hematopoietic malignancies. SIGNIFICANCE: We describe an integrative approach to identify noncoding variants in human leukemia, and reveal cohorts of variant-associated oncogenic and tumor-suppressive cis-regulatory elements including KRAS and PER2 enhancers. Our findings support a model in which noncoding regulatory variants connect enhancer dysregulation with nuclear receptor signaling to modulate gene programs in hematopoietic malignancies.See related commentary by van Galen, p. 646.This article is highlighted in the In This Issue feature, p. 627.
Project description:Gene enhancer elements are noncoding segments of DNA that play a central role in regulating transcriptional programs that control development, cell identity, and evolutionary processes. Recent studies have shown that noncoding single nucleotide polymorphisms (SNPs) that have been associated with risk for numerous common diseases through genome-wide association studies frequently lie in cell-type-specific enhancer elements. These enhancer variants probably influence transcriptional output, thereby offering a mechanistic basis to explain their association with risk for many common diseases. This review focuses on the identification and interpretation of disease-susceptibility variants that influence enhancer function. We discuss strategies for prioritizing the study of functional enhancer SNPs over those likely to be benign, review experimental and computational approaches to identifying the gene targets of enhancer variants, and highlight efforts to quantify the impact of enhancer variants on target transcript levels and cellular phenotypes. These studies are beginning to provide insights into the mechanistic basis of many common diseases, as well as into how we might translate this knowledge for improved disease diagnosis, prevention and treatments. Finally, we highlight five major challenges often associated with interpreting enhancer variants, and discuss recent technical advances that may help to surmount these challenges.
Project description:PurposeHeritable thoracic aortic disease can result from null variants in MYLK, which encodes myosin light-chain kinase (MLCK). Data on which MYLK missense variants are pathogenic and information to guide aortic disease management are limited.MethodsClinical data from 60 cases with MYLK pathogenic variants were analyzed (five null and two missense variants), and the effect of missense variants on kinase activity was assessed.ResultsTwenty-three individuals (39%) experienced an aortic event (defined as aneurysm repair or dissection); the majority of these events (87%) were aortic dissections. Aortic diameters were minimally enlarged at the time of dissection in many cases. Time-to-aortic-event curves showed that missense pathogenic variant (PV) carriers have earlier-onset aortic events than null PV carriers. An MYLK missense variant segregated with aortic disease over five generations but decreases MYLK kinase acitivity marginally. Functional Assays fail to identify all pathogenic variants in MYLK.ConclusionThese data further define the aortic phenotype associated with MYLK pathogenic variants. Given minimal aortic enlargement before dissection, an alternative approach to guide the timing of aortic repair is proposed based on the probability of a dissection at a given age.
Project description:BackgroundGenetic heterogeneity is common in inherited cardiac diseases. Next-generation sequencing gene panels are therefore suitable for genetic diagnosis. We describe the results of implementation of cardiomyopathy and arrhythmia gene panels in clinical care.MethodsWe present detection rates for variants with unknown (class 3), likely (class 4), and certain (class 5) pathogenicity in cardiogenetic gene panels since their introduction into diagnostics.ResultsIn 936 patients tested on the arrhythmia panel, likely pathogenic and pathogenic variants were detected in 8.8% (4.6% class 5; 4.2% class 4), and one or multiple class 3 variants in 34.8%. In 1970 patients tested on the cardiomyopathy panel, likely pathogenic and pathogenic variants were detected in 19.8% (12.0% class 5; 7.9% class 4), and one or multiple class 3 variants in 40.8%. Detection rates of all different classes of variants increased with the increasing number of genes on the cardiomyopathy gene panel. Multiple variants were detected in 11.7% and 28.5% of patients on the arrhythmia and cardiomyopathy panels respectively. In more recent larger versions of the cardiomyopathy gene panel the detection rate of likely pathogenic and pathogenic variants only slightly increased, but was associated with a large increase of class 3 variants.ConclusionOverall detection rates (class 3, 4, and 5 variants) in a diagnostic setting are 44% and 61% for the arrhythmia and cardiomyopathy gene panel respectively, with only a small minority of likely pathogenic and pathogenic variants (8.8% and 19.8% respectively). Larger gene panels can increase the detection rate of likely pathogenic and pathogenic variants, but mainly increase the frequency of variants of unknown pathogenicity.
Project description:Pathogenic variants in either the mitochondrial or nuclear genomes are associated with a diverse group of human disorders characterized by impaired mitochondrial function. Within this group, an increasing number of families have been identified, where Mendelian genetic disorders implicate defective mitochondrial RNA biology. The PDE12 gene encodes the poly(A)-specific exoribonuclease, involved in the quality control of mitochondrial non-coding RNAs. Here, we report that disease-causing PDE12 variants in three unrelated families are associated with mitochondrial respiratory chain deficiencies and wide-ranging clinical presentations in utero and within the neonatal period, with muscle and brain involvement leading to marked cytochrome c oxidase (COX) deficiency in muscle and severe lactic acidosis. Whole exome sequencing of affected probands revealed novel, segregating bi-allelic missense PDE12 variants affecting conserved residues. Patient-derived primary fibroblasts demonstrate diminished steady-state levels of PDE12 protein, whilst mitochondrial poly(A)-tail RNA sequencing (MPAT-Seq) revealed an accumulation of spuriously polyadenylated mitochondrial RNA, consistent with perturbed function of PDE12 protein. Our data suggest that PDE12 regulates mitochondrial RNA processing and its loss results in neurological and muscular phenotypes.
Project description:Accumulating evidence suggests that genetic variants in the SORL1 gene are associated with Alzheimer disease (AD), but a strategy to identify which variants are pathogenic is lacking. In a discovery sample of 115 SORL1 variants detected in 1908 Dutch AD cases and controls, we identified the variant characteristics associated with SORL1 variant pathogenicity. Findings were replicated in an independent sample of 103 SORL1 variants detected in 3193 AD cases and controls. In a combined sample of the discovery and replication samples, comprising 181 unique SORL1 variants, we developed a strategy to classify SORL1 variants into five subtypes ranging from pathogenic to benign. We tested this pathogenicity screen in SORL1 variants reported in two independent published studies. SORL1 variant pathogenicity is defined by the Combined Annotation Dependent Depletion (CADD) score and the minor allele frequency (MAF) reported by the Exome Aggregation Consortium (ExAC) database. Variants predicted strongly damaging (CADD score >30), which are extremely rare (ExAC-MAF <1 × 10-5) increased AD risk by 12-fold (95% CI 4.2-34.3; P=5 × 10-9). Protein-truncating SORL1 mutations were all unknown to ExAC and occurred exclusively in AD cases. More common SORL1 variants (ExAC-MAF≥1 × 10-5) were not associated with increased AD risk, even when predicted strongly damaging. Findings were independent of gender and the APOE-ɛ4 allele. High-risk SORL1 variants were observed in a substantial proportion of the AD cases analyzed (2%). Based on their effect size, we propose to consider high-risk SORL1 variants next to variants in APOE, PSEN1, PSEN2 and APP for personalized risk assessments in clinical practice.
Project description:Changes in the amino acid sequences of proteins cause thousands of human genetic diseases. However, only a subset of variants in any protein is typically pathogenic, with variants having a diversity of molecular consequences. Determining which of the thousands of possible variants in any protein have similar molecular effects is very challenging, but crucial for identifying pathogenic variants, determining disease mechanisms, understanding clinical phenotypic variation, and developing targeted therapeutics. Here we present a general method to classify variants by their molecular effects that we term intramolecular genetic interaction profiling. The approach relies on the principle that variants with similar molecular consequences have similar genetic interactions with other variants in the same protein. These intramolecular genetic interactions are straightforward to quantify for any protein with a selectable function. We apply intramolecular genetic interaction profiling to amyloid beta, the protein that aggregates in Alzheimer’s disease (AD) and is mutated in familial AD (fAD). Genetic interactions identify two classes of gain-of-function variants, with all known familial Alzheimer’s disease variants having very similar genetic interaction profiles, consistent with a common gain-of-function mechanism leading to pathology. We believe that intramolecular genetic interaction profiling is a powerful approach for classifying variants in disease genes that will empower rare variant association studies and the discovery of disease mechanisms.
Project description:Patients suspected of adenomatous polyposis were included. The criteria used were more than 10 polyps observed under colonoscopy, and pathological confirmation of adenoma. Clinical data and pedigree information were collected. The variants of 139 genes associated with different hereditary cancers and polyposis were screened by NGS, which was performed by Genetron Health on the HiSeqX-ten sequencing platform.