Frequency Of Loss-of-function Variants Research Articles

Abstract 5233: Germline CHEK2 variants and risk of lymphoma

Abstract Lymphoma is the sixth most commonly diagnosed cancer in the US. Genome-wide association studies have identified common variants associated with risk of specific lymphoma subtypes, but less is known about the contribution of rare inherited variants in the genetic architecture of lymphoma risk. CHEK2 is important to DNA repair and 2 small studies have found evidence of an association between CHEK2 variants and risk of lymphoma. Here, we investigated loss of function (LoF) variants in CHEK2 with risk of lymphoma (overall and subtypes). The study population included newly diagnosed lymphoma cases from Mayo who were enrolled in the Lymphoma SPORE Molecular Epidemiology Resource (MER). Controls were from the Mayo Clinic Biobank, from which we excluded a prior hematologic malignancy. Whole exome sequencing was performed by Regeneron on an Illumina NovaSeq panel (mean coverage of 48X). Variants were called using GATK v4 and variant annotation was performed using BioR. All LoF variants (nonsense, frameshift and consensus splice sites) in CHEK2 with a minor allele frequency < 0.5% were included in the analyses. Logistic regression was used to estimate odds ratio (OR) and 95% confidence intervals (CI) for the association between CHEK2mutation status and risk of lymphoma overall, and by lymphoma subtypes that had more than 5 mutation carriers, which included diffuse large B-cell (DLBCL), follicular (FL), and T-cell lymphoma (TCL). All analyses were adjusted for age (at diagnosis for cases and at enrollment for controls) and sex. A total of 4,852 lymphoma cases and 49,724 controls were included in this analysis. Median age for both cases and controls was 62 years (range 18-99 years). Males accounted for 57.5% (n=2,789) of the cases and 40.6% (n=20,186) of the controls. The DLBCL (23.6% of cases) and FL (23.3% of cases) subtypes were the most common; 7.6% of cases had TCL. A total of 407 (0.7%) individuals had a LoF variant. The frequency of LoF variants was 1.2% in lymphoma cases and 0.7% in controls. LoF variants were associated with increased risk of lymphoma overall (OR=1.77; 95%CI: 1.32-2.33), DLBCL (OR=2.07; 95%CI: 1.20-3.13), and TCL (OR=2.78; 95%CI: 1.178-5.50), but not FL (OR=1.31; 95%CI: 0.65-2.34). CHEK2 c.1100delC was the most frequently mutated variant in this population, accounting for 76% of all LoF variants. Individuals with a c.1100delC variant had an increased risk of lymphoma overall (OR=1.90; 95%CI: 1.37-2.58), DLBCL (OR=2.06; 95%CI: 1.09-3.54), and TCL (OR=3.17; 95%CI:1.24-6.58), but not FL (OR=1.05; 95%CI: 0.41-2.15). When restricted to cases, there was no significant difference in age at diagnosis (P=0.62) or sex (P=0.53) between LoF variant carriers and non-carriers. In this large lymphoma case-control study, CHEK2 LoF variants were associated with increased risk of lymphoma, demonstrating that rare inherited variants may play an important role in the etiology of lymphoma. Additional work is needed to investigate missense variants in CHEK2 and risk of lymphoma. Citation Format: Nicholas J. Boddicker, Raphael Mwangi, Dennis P. Robinson, Allison C. Rosenthal, Thomas M. Habermann, Andrew L. Feldman, Lisa M. Rimsza, Rebecca L. King, Melissa C. Larson, Brianna J. Gysbers, Stephen M. Ansell, Jithma P. Abeykoon, Grzegorz S. Nowakowski, Thomas E. Witzig, Anne J. Novak, Susan L. Slager, James R. Cerhan. Germline CHEK2 variants and risk of lymphoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5233.

Discovery and analyses of pathogenic variants in explanted hearts from primary cardiomyopathy patients

Abstract Background Dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM) are disorders of the myocardium that affect the structure and function of the heart. Purpose The primary aim of this study was to discover damaging genetic variants in myocardial tissue from patients with DCM or HCM, who underwent heart transplantation. Methods Whole exome sequencing was performed on myocardial tissue from 103 explanted hearts with diagnosis of cardiomyopathy; 80 DCM and 13 HCM. Sanger sequencing was performed to confirm the loss-of-function variants in genes known to be linked to cardiomyopathy. RNA sequencing was conducted to confirm copy number variation deletions detected in the cohort. Burden analysis was performed by comparing the frequency of variants found in the study cohort to the frequency in the population database gnomAD. Results Rare (minor allele frequency <1.0E-04) loss-of-function variants, deleterious missense variants, or copy number variation deletions, collectively described as damaging variants, were identified in cardiomyopathy genes in 42 of all 93 samples (45.2%). Damaging variants were identified in 37 of 80 DCM samples (46.3%) and 5 of 13 HCM samples (38.4%). The mean read depth for normal and variant allele were comparable. All the 28 loss-of-function variants in cardiomyopathy genes found in the cardiomyopathy cases were confirmed by Sanger sequencing. Two copy number variation deletions both in titin (TTN) were also detected and confirmed. Burden analyses showed that the genes TTN and lamin A/C (LMNA) had a higher frequency of loss-of function variants in the DCM cohort (17.5% and 3.75%, respectively) compared to the reference population with genome-wide significance (p=3.45E-22 and 4.34E-07, respectively). Furthermore, our analysis showed that deleterious missense variants in osteoclast-stimulating factor 1 (OSTF1), which previously has not been associated with cardiomyopathy, was highly enriched in the DCM cohort compared to the reference population (p=2.10E-06). Conclusions The frequency of damaging variants that are likely pathogenic (46.3%) is higher in DCM cases in this cohort compared to previous studies. These data indicate that patients with end-stage DCM are more likely to have a genetic cause for their disease. As read depth of variant and normal alleles were, these are likely germline and not mosaic variants, and can enable cascade testing in family members. Moreover, our study demonstrates that CNVs in TTN that alter the reading frame can cause DCM. Funding Acknowledgement Type of funding source: None

Germline variants in the MBD4 gene are rare in patients with uveal melanoma

AbstractPurposeThe mutation profile of uveal melanoma (UM) is unusual as these tumors generally have very few somatic events. Eight genes are recognized as drivers of UM tumorigenesis, typically consisting of one mutually exclusive mutation in GNAQ, GNA11, PLCB4 or CYSLTR2 combined with one mutually exclusive mutation in EIF1AX, SF3B1, SRSF2 or BAP1. Germline variants predisposing to UM have so far been described only in BAP1. Recently, four patients with UM were found with germline loss of function (LOF) variants in the methyl‐CpG binding domain 4 (MBD4) gene that was suggested to be a UM predisposition gene. Loss of functional MBD4 induces a hypermutated profile, making the tumor more susceptible to immune checkpoint inhibitors. We investigated MBD4 variants in patients with UM to identify pathogenic variants and to estimate their clinical relevance.MethodsSanger sequencing of MBD4 in 440 Finnish patients with uveal melanoma diagnosed from 2010 to 2017.ResultsEight rare (minor allele frequency in gnomAD Fin <0.5%) MBD4 missense variants were identified in 16 patients. One of them was likely pathogenic. The UM has not metastasized. The frequency of likely pathogenic MBD4 variants in Finnish patients with UM was 0.2% (95% CI, 0.01–1.3). No LOF variants were found. The frequency of LOF variants in the general population in Finland is 0.05%, according to the gnomAD database, suggesting one should occur by chance in every 2000 patients with UM.ConclusionsMBD4 variants do not seem to predispose to UM in Finland. Somatic loss of MBD4 function might still modify the tumor phenotype through accumulating mutations and changing the response of the tumor to immune checkpoint inhibitors. However, the utility of germline MBD4 sequencing is low.

Tolerance to Selenoprotein Loss Differs between Human and Mouse.

Mouse has emerged as the most common model organism in biomedicine. Here, we analyzed the tolerance to the loss-of-function (LoF) of selenoprotein genes, estimated from mouse knockouts and the frequency of LoF variants in humans. We found not only a general correspondence in tolerance (e.g., GPX1, GPX2) and intolerance (TXNRD1, SELENOT) to gene LoF between humans and mice but also important differences. Notably, humans are intolerant to the loss of iodothyronine deiodinases, whereas their deletion in mice leads to mild phenotypes, and this is consistent with phenotype differences in selenocysteine machinery loss between these species. In contrast, loss of TXNRD2 and GPX4 is lethal in mice but may be tolerated in humans. We further identified the first human SELENOP variants coding for proteins varying in selenocysteine content. Finally, our analyses suggested that premature termination codons in selenoprotein genes trigger nonsense-mediated decay, but do this inefficiently when UGA codon is gained. Overall, our study highlights differences in the physiological importance of selenoproteins between human and mouse.