Investigation of the effect of ADA2 mutant allele expression levels on disease severity in adenosine deaminase 2 deficiency disease

DADA2 is autosomal recessive disease caused by loss-of-function mutations in the ADA2 gene. For the same constitutive mutation in DADA2, the age of onset, frequency and severity of symptoms of the disease vary. In a previous study, we found differences in short ADA2 expression levels in individuals homozygous carrying the splice site mutation (c.973-2A>G), which causes exon 7 skipping in the ADA2 gene. In this study, it was aimed to investigate the reason for variability of the mutant allele expression levels and severity of disease in different cell types of the patients. Inflammation was triggered by applying Lipopolysaccharide (LPS) to the cells obtained from patients. Mutant and normal mRNA expression levels were analyzed by qRT-PCR and ADA2 enzyme activity was measured. It was found that ADA2 enzyme activity was decreased in plasma of the patients. However, ADA2 enzyme activity was not detected in cell culture. It was determined that the LPS application to the cells did not cause significant difference in ADA2 expression. Exon 7 skipped mutant ADA2 expression was observed in lymphocytes and neutrophils of the patients, and wild type ADA2 expression was observed in monocyte. Expression of wild type ADA2 was observed in PBMC and neutrophils of heterozygous healthy person. These results suggest that the severity of the disease and the clinical phenotype may vary depending on the cell type in which mutant ADA2 is expressed. This study is the first functional study that ADA2 gene expression and ADA2 enzyme activity were investigated using different cells. Key Words: DADA2, CECR1, ADA2, LPS, mRNA