PENK and Patent ductus arteriosus: One group has demonstrated that methylation levels in terms of the MI of four genes, secreted protein acidic and rich in cysteine (SPARC), ubiquitin carboxy-terminal hydrolase L1 (UCHL1), neuronal pentraxin 2 (NPTX2), and proenkephalin (PENK), can distinguish between HC, CP, and PDA [47].