Impact of DNA source on genetic variant detection from human whole-genome sequencing data.

BACKGROUND: Whole blood is currently the most common DNA source for whole-genome sequencing (WGS), but for studies requiring non-invasive collection, self-collection, greater sample stability or additional tissue references, saliva or buccal samples may be preferred. However, the relative quality of sequencing data and accuracy of genetic variant detection from blood-derived, saliva-derived and buccal-derived DNA need to be thoroughly investigated. METHODS: Matched blood, saliva and buccal samples from four unrelated individuals were used to compare sequencing metrics and variant-detection accuracy among these DNA sources. RESULTS: We observed significant differences among DNA sources for sequencing quality metrics such as percentage of reads aligned and mean read depth (p<0.05). Differences were negligible in the accuracy of detecting short insertions and deletions; however, the false positive rate for single nucleotide variation detection was slightly higher in some saliva and buccal samples. The sensitivity of copy number variant (CNV) detection was up to 25% higher in blood samples, depending on CNV size and type, and appeared to be worse in saliva and buccal samples with high bacterial concentration. We also show that methylation-based enrichment for eukaryotic DNA in saliva and buccal samples increased alignment rates but also reduced read-depth uniformity, hampering CNV detection. CONCLUSION: For WGS, we recommend using DNA extracted from blood rather than saliva or buccal swabs; if saliva or buccal samples are used, we recommend against using methylation-based eukaryotic DNA enrichment. All data used in this study are available for further open-science investigation.

Polymorphisms associated with expression of BPIFA1/BPIFB1 and lung disease severity in cystic fibrosis.

BPI fold containing family A, member 1 (BPIFA1) and BPIFB1 are putative innate immune molecules expressed in the upper airways. Because of their hypothesized roles in airway defense, these molecules may contribute to lung disease severity in cystic fibrosis (CF). We interrogated BPIFA1/BPIFB1 single-nucleotide polymorphisms in data from an association study of CF modifier genes and found an association of the G allele of rs1078761 with increased lung disease severity (P = 2.71 × 10(-4)). We hypothesized that the G allele of rs1078761 is associated with decreased expression of BPIFA1 and/or BPIFB1. Genome-wide lung gene expression and genotyping data from 1,111 individuals with lung disease, including 51 patients with CF, were tested for associations between genotype and BPIFA1 and BPIFB1 gene expression levels. Findings were validated by quantitative PCR in a subset of 77 individuals. Western blotting was used to measure BPIFA1 and BPIFB1 protein levels in 93 lung and 101 saliva samples. The G allele of rs1078761 was significantly associated with decreased mRNA levels of BPIFA1 (P = 4.08 × 10(-15)) and BPIFB1 (P = 0.0314). These findings were confirmed with quantitative PCR and Western blotting. We conclude that the G allele of rs1078761 may be detrimental to lung function in CF owing to decreased levels of BPIFA1 and BPIFB1.