Increasing the diagnostic yield of exome sequencing by copy number variant analysis

As whole exome sequencing (WES) becomes more widely used in the clinical realm, a wealth of unanalyzed information will be routinely generated. Using WES read depth data to predict copy number variation (CNV) could extend the diagnostic utility of this previously underutilized data by providing clinically important information such as previously unsuspected deletions or duplications. We evaluated ExomeDepth, a free R package, in addition to an aneuploidy prediction method, to detect CNVs in WES data. First, in a blinded pilot study, five out of five genomic alterations were correctly identified from clinical samples with previously defined chromosomal gains or losses, including submicroscopic deletions, duplications, and chromosomal trisomy. We then examined CNV calls among 53 patients participating in the NCGENES research study and undergoing WES, who had existing clinical chromosomal microarray (CMA) data that could be used for validation. For unique CNVs that overlap well with WES coverage regions, sensitivity was 89% for deletions and 65% for duplications. While specificity of the algorithm calls remains a concern, this is less of an issue at high threshold filtering levels. When applied to all 672 patients from the exome sequencing study, ExomeDepth identified eleven diagnostically relevant CNVs ranging in size from a two exon deletion to whole chromosome duplications, as well as numerous other CNVs with varying clinical significance. This opportunistic analysis of WES data yields an additional 1.6% of patients in this study with pathogenic or likely pathogenic CNVs that are clinically relevant to their phenotype as well as clinically relevant secondary findings. Finally, we demonstrate the potential value of copy number analysis in cases where a single heterozygous likely or known pathogenic single nucleotide alteration is identified in a gene associated with an autosomal recessive condition.

Genetic Complexity of Mitral Valve Prolapse Revealed by Clinical and Genetic Evaluation of a Large Family

BACKGROUND

A genetic component to familial mitral valve prolapse (MVP) has been proposed for decades. Despite this, very few genes have been linked to MVP. Herein is described a four-generation pedigree with numerous individuals affected with severe MVP, some at strikingly young ages.

METHODS

A detailed clinical evaluation performed on all affected family members demonstrated a spectrum of MVP morphologies and associated phenotypes.

RESULTS

Linkage analysis failed to identify strong candidate loci, but revealed significant regions, which were investigated further using whole-exome sequencing of one of the severely affected family members. Whole-exome sequencing identified variants in this individual that fell within linkage analysis peak regions, but none was an obvious pathogenic candidate. Follow up segregation analysis of all exome-identified variants was performed to genotype other affected and unaffected individuals in the family, but no variants emerged as clear pathogenic candidates. Two notable variants of uncertain significance in candidate genes were identified: p.I1013S in PTPRJ at 11p11.2 and FLYWCH1 p.R540Q at 16p13.3. Neither gene has been previously linked to MVP in humans, although PTPRJ mutant mice display defects in endocardial cushions, which give rise to the cardiac valves. PTPRJ and FLYWCH1 expression was detected in adult human mitral valve cells, and in-silico analysis of these variants suggests they may be deleterious. However, neither variant segregated completely with all of the affected individuals in the family, particularly when 'affected' was broadly defined.

CONCLUSIONS

While a contributory role for PTPRJ and FLYWCH1 in this family cannot be excluded, the study results underscored the difficulties involved in uncovering the genomic contribution to MVP, even in apparently Mendelian families.

Co-occurring Down syndrome and SUCLA2-related mitochondrial depletion syndrome

Mitochondrial DNA depletion syndrome 5 (MIM 612073) is a rare autosomal recessive disorder caused by homozygous or compound heterozygous pathogenic variants in the beta subunit of the succinate-CoA ligase gene located within the 13q14 band. We describe two siblings of Hispanic descent with SUCLA2-related mitochondrial depletion syndrome (encephalomyopathic form with methylmalonic aciduria); the older sibling is additionally affected with trisomy 21. SUCLA2 sequencing identified homozygous p.Arg284Cys pathogenic variants in both patients. This mutation has previously been identified in four individuals of Italian and Caucasian descent. The older sibling with concomitant disease has a more severe phenotype than what is typically described in patients with either SUCLA2-related mitochondrial depletion syndrome or Down syndrome alone. The younger sibling, who has a normal female chromosome complement, is significantly less affected compared to her brother. While the clinical and molecular findings have been reported in about 50 patients affected with a deficiency of succinate-CoA ligase caused by pathogenic variants in SUCLA2, this report describes the first known individual affected with both a mitochondrial depletion syndrome and trisomy 21.

Germline Analysis from Tumor-Germline Sequencing Dyads to Identify Clinically Actionable Secondary Findings

PURPOSE

To evaluate germline variants in hereditary cancer susceptibility genes among unselected cancer patients undergoing tumor-germline sequencing.

EXPERIMENTAL DESIGN

Germline sequence data from 439 individuals undergoing tumor-germline dyad sequencing through the LCCC1108/UNCseq™ (NCT01457196) study were analyzed for genetic variants in 36 hereditary cancer susceptibility genes. These variants were analyzed as an exploratory research study to determine whether pathogenic variants exist within the germline of patients undergoing tumor-germline sequencing. Patients were unselected with respect to indicators of hereditary cancer predisposition.

RESULTS

Variants indicative of hereditary cancer predisposition were identified in 19 (4.3%) patients. For about half (10/19), these findings represent new diagnostic information with potentially important implications for the patient and their family. The others were previously identified through clinical genetic evaluation secondary to suspicion of a hereditary cancer predisposition. Genes with pathogenic variants included ATM, BRCA1, BRCA2, CDKN2A, and CHEK2 In contrast, a substantial proportion of patients (178, 40.5%) had Variants of Uncertain Significance (VUS), 24 of which had VUS in genes pertinent to the presenting cancer. Another 143 had VUS in other hereditary cancer genes, and 11 had VUS in both pertinent and nonpertinent genes.

CONCLUSIONS

Germline analysis in tumor-germline sequencing dyads will occasionally reveal significant germline findings that were clinically occult, which could be beneficial for patients and their families. However, given the low yield for unexpected germline variation and the large proportion of patients with VUS results, analysis and return of germline results should adhere to guidelines for secondary findings rather than diagnostic hereditary cancer testing. Clin Cancer Res; 22(16); 4087-94. ©2016 AACRSee related commentary by Mandelker, p. 3987.