TKT and hyperinsulinemic hypoglycemia, familial, 4: This viral TK deficiency demonstrates an identical cross-resistance pattern among all the nucleoside analogs from acyclovir, valacyclovir, penciclovir, and famciclovir among immunocompetent individuals, but the higher prevalence among immunocompromised patients with severity depending on underlying diseases such as hematologic transplants, stem cell replacements or solid organ surgeries [107,108].