title: HC9
design: Total RNA was extracted from serum by TRIzol (Thermo-Fisher-Scientific, Shanghai, China). Next, RNAs with the length of 18-30 nucleotides were enriched by polyacrylamide gel electrophoresis. Subsequently, the 5 'and 3' end adaptors were ligated to the RNA. Then, the ligation products were reverse transcribed, and 140-160 base products were collected to construct cDNA library