Step I T-cell disorder question

[Fungi121]

Can someone explain to me how disorders that affect CD4 cells (ie, thymic aplasia in DiGeorge) do not cause SCID (ie, deficiency if IL-2R)?

I feel that thymic aplasia > no Cd4/cd8 > no activation of B-cells > scid? Where am I going wrong?

Or does thymic aplasia actually cause scid?

 

[CherryRedDracul]

DiGeorge syndrome (DGS) presents with varying symptoms. In reality, most people affect by DGS only have a mild deficit in T cell numbers, and the thymus is not always absent (could be hypoplastic as well).

In complete DGS, however, there is thymic aplasia, and you can consider it to be a form of SCID.