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.
We used a variety of sequencing technologies, ADA2 enzymatic testing, and molecular methods including qRT-PCR and MLPA.
Exome sequencing identified heterozygosity for the known pathogenic variant ADA2: 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 of ADA2 was identified in a 5-year-old female with features consistent with Diamond-Blackfan anemia (DBA). The duplication was missed by Sanger sequencing of ADA2, 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.
ADA2 pathogenic 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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We would like to thank the patients, the families, and the healthy controls for their enthusiastic support during this study. We also thank Adelani Adeleye, Camille Alba, Dagmar Bacikova, Daniel N. Hupalo, Elisa McGrath Martinez, Anthony R. Soltis, Gauthaman Sukumar, and Xijun Zhang from the American Genome Center (Uniformed Services University of the Health Sciences, Bethesda, MD, USA) and Harvey B. Pollard and Matthew D. Wilkerson from the Department of Anatomy, Physiology & Genetics (Uniformed Services University of the Health Sciences, Bethesda, MD, USA).
This research was financially supported by the Intramural Research Programs of the NHGRI and the NIH Clinical Center. The study was additionally supported by a NIDCR, NIH intramural research grant (1ZIADE000695) to JAC and a DDIR Innovation Award to JAC and DGM. Genome sequencing was supported by the Department of Defense (award W81XWH-09-2-0128). This work utilized the computational resources of the NIH HPC Biowulf cluster. OS is supported by the German Research Foundation.
Conflict of Interest
The authors declare that they have no conflict of interest.
The study was approved by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)/National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) Institutional Review Board.
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Schnappauf, O., Zhou, Q., Moura, N.S. et al. Deficiency of Adenosine Deaminase 2 (DADA2): Hidden Variants, Reduced Penetrance, and Unusual Inheritance. J Clin Immunol 40, 917–926 (2020). https://doi.org/10.1007/s10875-020-00817-3
- Exome sequencing
- genome sequencing
- deficiency of adenosine deaminase 2
- loss-of-function variants