PARN and pemphigus foliaceus: Genetic spontaneous PF can be further classified into familial IPF, typically associated with surfactant proteins A and C (SP-A and SP-C) mutations, sporadic IPF linked to mutations in poly(A)-specific ribonuclease (PARN), telomerase reverse transcriptase (TERT), regulator of telomere elongation helicase 1 (RTEL1), telomerase RNA component (TERC), and gain-of-function mucin 5B (MUC5B)-induced IPF.