Extrapolation of these findings to the in vivo situation indicates that NSHPT would result from a complete loss of expression of CaSR at the plasma membrane whereas in FHH1 there would be in total 75% of normal levels of CaSR (WT and mutant), 67% of which would have a three-fold reduced [Ca2+]o affinity compared to normal. The gene discussed is CASR; the disease is neonatal severe primary hyperparathyroidism.