STAT Prenatal Whole Exome Sequencing, TRIO

The purpose of this test is to find the underlying genetic cause for prenatal findings.

Whole exome sequencing is performed on genomic DNA using the Agilent SureSelect Clinical Research Exome v3 targeted sequence capture method to enrich for the exome. Direct sequencing of the amplified captured regions was performed using 2X150bp reads on Illumina next generation sequencing (NGS) systems. A base is considered to have sufficient coverage at 20X and an exon is considered fully covered if all coding bases plus three nucleotides of flanking sequence on either side are covered at 20X or more. A list of low coverage regions, if any, is available upon request. Alignment to the human reference genome (hg19) is performed and annotated variants are identified in the targeted region. Variants reviewed have a minimum coverage of 8X and an alternate allele frequency of 20% or higher. Indels and single nucleotide variants (SNVs) may be confirmed by Sanger sequence analysis before reporting at director discretion. Mitochondrial DNA is sequenced and analyzed using the same pipeline. Mitochondrial variants are reported at a minimum of 5% heteroplasmy if the average coverage of the mitochondrial genome is 1000x. This assay cannot detect variants in regions of the exome that are not covered, such as deep intronic, promoter, and enhancer regions, and areas containing large numbers of tandem repeats. Genes and/or exons located in pseudogene regions are not covered in this assay. Copy number variation (CNV) analysis is designed to detect deletions and duplications of three exons or more; in some instances, due to the size of the exons or other factors, not all CNVs may be analyzed.  This assay does not interrogate CNVs in mitochondrial DNA. CNV analysis will not detect tandem repeats, balanced alterations (reciprocal translocations, Robertsonian translocations, inversions, and balanced insertions), methylation abnormalities, triploidy, and genomic imbalances in segmentally duplicated regions. This assay is not designed to detect mosaicism; possible cases of mosaicism may be investigated at the discretion of the laboratory director. Primary data analysis is performed using Illumina bcl2fastq converter v2.19. Secondary analysis is performed using Illumina DRAGEN Bio-IT Platform v.3.4.12. Tertiary data analysis is performed using SnpEff v4.3t and PerkinElmer’s internal ODIN v.1.01 software. CNV and absence of heterozygosity are assessed using BioDiscovery’s NxClinical v6.1 software.