ADA and myeloid sarcoma: In particular, the altered activity of the enzyme adenosine deaminase (ADA) is associated with the toxic accumulation of triphosphorylated deoxyadenosine and lymphocyte depletion, as shown in ADA genetic deficiency and in patients treated with cladribine (2-chloro-2′-deoxyadenosine) tablets, a purine deoxynucleoside analogue resistant to the action of ADA, approved for the treatment of highly active relapsing–remitting (RR)MS [8,9].