Identification of ITK deficiency as a novel genetic cause of idiopathic CD4+ T-cell lymphopenia.

To the editor: Idiopathic CD4 lymphopenia represents a heterogeneous group of combined primary immunodeficiencies with markedly reduced CD4+ T-cell counts. Although several genetic etiologies including MHC class II deficiency[1][1] or mutations in RAG1 ,[2][2] MST1 ,[3][3] or LCK [4][4] have been