Journal
JOURNAL OF CLINICAL IMMUNOLOGY
Volume 40, Issue 6, Pages 917-926Publisher
SPRINGER/PLENUM PUBLISHERS
DOI: 10.1007/s10875-020-00817-3
Keywords
Exome sequencing; genome sequencing; deficiency of adenosine deaminase 2; loss-of-function variants
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Funding
- Intramural Research Programs of the NHGRI
- NIH Clinical Center
- NIDCR, NIH [1ZIADE000695]
- Department of Defense [W81XWH-09-2-0128]
- German Research Foundation
- DDIR Innovation Award
- NATIONAL HUMAN GENOME RESEARCH INSTITUTE [ZIAHG200372] Funding Source: NIH RePORTER
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Purpose Deficiency of adenosine deaminase 2 (DADA2) is an autosomal recessive disorder that manifests with fever, early-onset vasculitis, strokes, and hematologic dysfunction. This study aimed to identify disease-causing variants by conventional Sanger and whole exome sequencing in two families suspected to have DADA2 and non-confirmatory genotypes. ADA2 enzymatic assay confirmed the clinical diagnosis of DADA2. Molecular diagnosis was important to accurately identify other family members at risk. Methods We used a variety of sequencing technologies, ADA2 enzymatic testing, and molecular methods including qRT-PCR and MLPA. Results Exome sequencing identified heterozygosity for the known pathogenic variantADA2: c.1358A>G, p.Tyr453Cys in a 14-year-old female with a history of ischemic strokes, livedo, and vasculitis. No second pathogenic variant could be identified. ADA2 enzymatic testing in combination with quantitative RT-PCR suggested a loss-of-function allele. Subsequent genome sequencing identified a canonical splice site variant, c.-47+2T>C, within the 5 ' UTR of ADA2. Two of her unaffected siblings were found to carry the same two pathogenic variants. A homozygous 800-bp duplication comprising exon 7 ofADA2was identified in a 5-year-old female with features consistent with Diamond-Blackfan anemia (DBA). The duplication was missed by Sanger sequencing ofADA2, chromosomal microarray, and exome sequencing but was detected by MLPA in combination with long-read PCR sequencing. The exon 7 duplication was also identified in her non-symptomatic father and younger sister. Conclusions ADA2pathogenic variants may not be detected by conventional sequencing and genetic testing and may require the incorporation of additional diagnostic methods. A definitive molecular diagnosis is crucial for all family members to make informed treatment decisions.
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