DNAJC18 is a DnaJ heat shock protein family member (Hsp40) that functions as a molecular chaperone involved in multiple biological processes. Primary function: DNAJC18 localizes to the endoplasmic reticulum (ER) membrane where it participates in protein folding and cellular responses to misfolded proteins through Hsp70 protein binding 1. In viral infection, DNAJC18 regulates polyomavirus penetration across the ER membrane by coordinating recruitment of DNAJB12:DNAJB14 into SV40-induced foci, facilitating cytosolic entry of the virus [PMID:25631089, cited in UniProt annotation]. Disease relevance: DNAJC18 has emerged as a significant gene in cardiac homeostasis and neurodegeneration. Loss-of-function mutations in DNAJC18 are associated with congenital heart disease and developmental cardiac abnormalities, with human variants categorized as variants of unknown relevance (VUR); UK Biobank validation demonstrates associations with altered left ventricular systolic function 2. Additionally, rare missense variants in DNAJC18 show suggestive association with Parkinson's disease in both sporadic early-onset and familial forms 1. The gene also influences heat stress response and fat deposition in livestock, indicating roles in metabolic homeostasis and thermoregulation 3. Clinical significance: DNAJC18 represents a previously underappreciated gene with potential causal functions in congenital heart disease and neurodegenerative disease pathogenesis.