Immunodeficiency 13, also known as idiopathic cd4 lymphopenia, is related to progressive multifocal leukoencephalopathy and lymphopenia. An important gene associated with Immunodeficiency 13 is UNC119 (Unc-119 Lipid Binding Chaperone), and among its related pathways/superpathways are T-cell activation SARS-CoV-2 and Hematopoietic Stem Cells and Lineage-specific Markers. The drugs Lenograstim and Plerixafor have been mentioned in the context of this disorder. Affiliated tissues include t cells and bone marrow, and related phenotypes are lymphopenia and recurrent pneumonia