Neuroendocrine secretory granules. Binds keratan sulfate chains. May be proteolytically processed to give rise to a number of active peptides. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Most affected individuals have defects in methylation of the gene. In some cases microdeletions involving the STX16 appear to cause loss of methylation at exon A/B of GNAS, resulting in PHP1B. Paternal uniparental isodisomy have also been observed. The disease is caused by variants affecting the gene represented in this entry. This protein is produced by a bicistronic gene which also produces the ALEX protein from an overlapping reading frame. The GNAS locus is imprinted in a complex manner, giving rise to distinct paternally, maternally and biallelically expressed proteins. The XLas isoforms are paternally derived, the Gnas isoforms are biallelically derived and the Nesp55 isoforms are maternally derived. Shares no sequence similarity with other isoforms due to a novel first exon containing the entire reading frame spliced to shared exon 2 so that exons 2-13 make up the 3'-UTR. Belongs to the NESP55 family.