Lack of Tregs in a combined immunodeficiency due to MALT1 mutations (compound heterozygous splice acceptor and de novo deletion) has been recently described in a male infant who developed generalized rash, intestinal inflammation, and severe infections including persistent cytomegalovirus.137 MALT1 is a paracaspase with a central role in the activation of lymphocytes and other immune cells including myeloid cells, mast cells, and NK cells. The gene discussed is MALT1; the disease is immune system disorder.