Analysis of the results from phage ELISAs suggested that a major CaSR epitope was localized in the N-terminal extracellular domain of the CaSR at amino acid residues 41–69 with antibody reactivity demonstrated in 12 of 12 (100%) of APS1 patients and the single patient with AHH (Table 4). The gene discussed is CASR; the disease is autoimmune polyendocrine syndrome type 1.