PTH and pseudohypoparathyroidism type 1A: Pseudohypoparathyroidism 1A (PHP1A) is caused by inactivating variants involving the maternal allele of the GNAS gene encoding Gsα, the alpha-subunit of the stimulatory G protein.2,3 Pseudohypoparathyroidism 1A belongs to a large group of rare diseases that share common clinical features such as brachydactyly and end-organ resistance to PTH because of impaired signaling downstream of the PTH1R and other G protein-coupled receptors (GPCRs).