ADA and lymphopenia: P21 was a male of European descent without a documented family history of malignancy, who presented with a CMV primary infection at the age of 4 months and was diagnosed with ADA-SCID for profound lymphopenia (lymphocytes 0.3 ×10^9/L) and biallelic pathogenic variants (c.455T>C [p.Leu152Pro] and c.478+6T>C) in the ADA gene (Table 1).