PRH1 (proline rich protein HaeIII subfamily 1) encodes acidic proline-rich proteins (PRPs) that function as highly potent inhibitors of calcium phosphate crystal growth, providing protective and reparative effects for dental enamel integrity 1. Located on chromosome 12.2, PRH1 exists as multiple allelic variants (Pa, Db, PIF, and As) that differ in their amino acid sequences, including cysteine substitutions and repeat regions affecting proteolytic processing 12. These PRH1 polymorphisms encode salivary receptors for indigenous oral bacteria and significantly influence individual susceptibility to dental caries 3. Children with high-susceptibility PRH1 phenotypes (P4a) develop substantially more caries (3.9-fold increase) than low-susceptibility phenotypes (P1), independent of traditional risk factors like sugar consumption or oral hygiene, suggesting genetically-determined predisposition 3. The PRH1 phenotype interacts with Streptococcus mutans virulence phenotypes to specify distinct oral microbial profiles affecting caries progression, with resistant phenotypes requiring high-virulence bacterial infection for disease development, while susceptible phenotypes develop caries from broader polymicrobial flora 4. PRH1-encoded proteins are highly specific salivary markers useful for forensic identification, with PRH1/2 ELISAs showing greater specificity for saliva than statherin-based assays 5.