ADA2 and Bone marrow hypocellularity: More recently, work by Lee and colleagues evaluated the nature of the mutation and suggested that, regardless of the location in the ADA2 gene, missense mutations that allow residual catalytic activity are more frequently associated with vasculopathy, whereas bone marrow failure and pure red cell aplasia in DADA2 patients are more frequently associated with nonsense variants, insertions/deletions and particular missense variants in ADA2 leading to abrogation (<3% of normal) of catalytic activity (12).