rOBBINS BASIC PATHOLOGY 9TH EDITION Chapter diseases of immunity. page no 143. very low activity of adenosine deaminase in sample of red cells and high levels of dATP is consistent with diagnosis of SCID (severe combined immuno deficiency disease) . so answer is option 2. Defects in Lymphocyte Activation Rare patients with mutations in genes required for T cell activation have been identified that manifest with defective cell-mediated immunity or a phenotype resembling SCID. One of the interesting ones is a mutation in a transcription factor that is required for the TH17 response. The resulting disease manifestations include fungal (and occasionally bacterial) skin infections and chronic mucocutaneous candidiasis. By contrast, mutations in genes involved in TH1 responses result in susceptibility to infections with atypical mycobacteria. These observations emphasize the impoance of TH17 cells for defense against fungal infec- tions and of TH1 cells for combating intracellular bacterial infections. Mutations in genes encoding calcium channel proteins, and other components of T cell signaling, also have been described.