Given the task definition and input, reply with output. In this task, you are given a sentence. You are expected to recognize the name of gene or protein. Although there might be several correct answers, you need to write one of them.

Analysis of exon 2 of the factor IX gene revealed a C - - > T mutation in codon 10 of the propeptide region , resulting in the substitution of alanine by valine .
factor IX gene