CASR and neonatal severe primary hyperparathyroidism: However, NSHPT has also been described in a small number of patients with heterozygous CaSR mutations, and it has been hypothesised that the clinical presentation of patients with heterozygous mutations is likely influenced by the location of the mutant residue, as well as intrauterine exposure to maternal calcium and vitamin D, and the presence of other CaSR polymorphisms that could act as genetic modifiers to influence activity of the receptor [12–14].