Stx16, short for syntaxin-16, is a gene with its function potentially related to the processes occurring at the GNAS locus. The GNAS locus is crucial as it encodes the alpha-subunit of the stimulatory G protein (Gsα) and its splice variants, and is involved in parent-specific methylation changes at several differentially methylated regions (DMRs) [1].

Mutations in Stx16 are significantly associated with pseudohypoparathyroidism (PHP), especially autosomal dominant PHP type Ib (AD-PHP1B). Maternally inherited STX16 deletions, such as the commonly observed exon 2-6 deletion, cause loss of methylation at GNAS exon A/B, reducing Gsα expression and leading to PTH-resistant hypocalcemia, hyperphosphatemia, and possible resistance to other hormones [1,2,3,4,5,6]. In a 39-year-old male PHP1B patient, a half-reduced copy number of STX16 exon 5-7 was detected along with loss of methylation at GNAS exon A/B [2]. Also, early identification of STX16 deletion-causing variants in children of affected or unaffected female carriers can help prevent hypocalcemia and associated complications as PTH levels increase several years before overt hypocalcemia develops [3].

In conclusion, Stx16 is closely linked to the development of AD-PHP1B through its impact on GNAS locus methylation and Gsα expression. Understanding the role of Stx16 in this disease through genetic analysis of patients helps in early diagnosis and treatment planning for preventing hypocalcemia and related sequelae.