The protein encoded by this gene is a member of the somatotropin/prolactin family of hormones which play an important role in growth control. The gene, along with four other related genes, is located at the growth hormone locus on chromosome 17 where they are interspersed in the same transcriptional orientation\; an arrangement which is thought to have evolved by a series of gene duplications. Although the five genes share a remarkably high degree of sequence identity, they are expressed selectively in different tissues. This particular family member is expressed in placental villi, although it was originally thought to be a pseudogene. In fact, alternative splicing suggests that the majority of the transcripts would be unable to express a secreted protein. Alternatively spliced transcript variants encoding different isoforms have been identified.