FASLG and hyperinsulinemic hypoglycemia, familial, 4: Susceptibility to infections is rare, mostly attributed to splenectomy or autoimmune neutropenia.135 Patients with Fas deficiency typically display marked elevations in CD4-CD8- double-negative T cells.136 Other typical laboratory findings include elevated vitamin B12, IL-10, and soluble Fas ligand (FasL/CD95L) levels.