PPIL1 (peptidylprolyl isomerase like 1) is a nuclear cyclophilin that functions as a critical component of the major spliceosome, playing essential roles in pre-mRNA splicing and embryonic brain development 1. As a peptidyl-prolyl isomerase, PPIL1 catalyzes the cis-trans isomerization of proline imidic peptide bonds, including prolyl peptide bond isomerization in the spliceosomal component PRP17 1. The protein forms an active isomerase-substrate interaction with PRP17, though its function in splicing appears independent of its enzymatic activity 1. PPIL1 is ubiquitously expressed with highest levels in heart tissue and localizes to the nucleus and nucleolus 2. Biallelic mutations in PPIL1 cause pontocerebellar hypoplasia type 14 (PCH14), a severe neurodegenerative disorder characterized by microcephaly, cerebellar hypoplasia, and developmental delays 13. Loss of PPIL1 function disrupts splicing integrity, particularly affecting short, GC-rich introns and genes involved in brain disorders, leading to neuron-specific apoptosis 1. Additionally, PPIL1 overexpression has been associated with colon cancer cell growth through interactions with transcriptional regulators SNW1/SKIP and stathmin 4. The protein also participates in complement-mediated tumor metastasis pathways 5.