The imprinted GNAS cluster, located on chromosome 2 in mice and chromosome 20 in humans, contains transcripts that are maternally, paternally, and/or biallelically expressed. Neuroendocrine secretory protein 55 (NESP55) is encoded by an upstream exon of the GNAS1 gene, which is expressed exclusively from the maternal allele []. It is a neuroendocrine secretory granule protein originally identified by screening cDNA libraries from bovine chromaffin cells with antibody against secretogranin II []. It belongs to the granin family, whose members are involved in endocrine and neuronal secretory pathways [].NESP55 has been shown to act as biomarkers for endocrine and neuroendocrine tumours and implicated in cell growth []. It has been linked to pseudohypoparathyroidism type Ib (PHP-1b), an imprinted human disorder associated with methylation changes at one or several differentially methylated regions at the GNAS locus [].
