Haploinsufficiency of A20 with a novel mutation of deletion of exons 2-3 of TNFAIP3.

OBJECTIVES: Haploinsufficiency of A20 (HA20) due to loss-of-function mutations of TNFAIP3 leads to an autoinflammatory disease. These mutations produce a premature termination codon in most cases of HA20. However, exon deletion has not been reported. METHODS: Genomic DNA was extracted from the peripheral blood of the patient clinically suspected of HA20. We examined autoinflammatory disease-causing genes and performed a multiplex ligation-dependent probe amplification (MLPA) assay for copy number analysis. Next, to determine the disconnection point, genomic DNA was amplified with long-range PCR and sequenced. Finally, western blotting was carried out to measure A20 protein expression in mitogen phytohaemagglutinin (PHA)-induced T-cell blasts from the patient and a healthy volunteer. RESULTS: Targeted next-generation sequencing found no pathogenic mutation, but copy number variation (CNV) analysis suggested a heterozygous deletion of exons 2-3. The MLPA assay and long-range PCR confirmed the mutation. Western blotting analysis indicated a marked decrease in expression of A20 protein from the patient compared to a normal control. The results showed that this deletion was a pathogenic mutation. CONCLUSION: This study demonstrates a novel mutation resulting in a deletion of exons 2-3 of TNFAIP3. MLPA analysis is a useful initial screening method for HA20 patients.