Genetic polymorphism of PIF (parotid isoelectric focusing variant) proteins with linkage to the PPP (parotid proline-rich protein) gene complex.

Genetic polymorphism is found among the PIF (parotid isoelectric focusing variant) salivary proteins after separation by prolonged isoelectric focusing in pH 3.5-5.2 urea polyacrylamide slab gels subsequently stained for protein. Two PIF proteins are either present (PIF+) or absent (PIF-) from all salivas. The phenotypes are determined by autosomal inheritance of two alleles, PIF+ and PIF-. Gene frequencies in randomly collected samples show marked racial differences: among 148 whites, PIF+ is 0.66 and PIF- is 0.34; among 90 blacks, PIF+ is 0.35 and PIF- is 0.65; among 78 Chinese, PIF+ is 0.56 and PIF- is 0.44. Studies in 41 families including 129 children support the interpretation of control of PIF by a single autosomal locus. In 8 PIF+ X PIF- matings, there were 8 PIF- (6.34 expected) children. In 33 PIF+ X PIF+ matings, there were 7 PIF- (6.70 expected) children. Linkage studies indicate that PIF is closely linked to the proline-rich protein (PPP) gene complex (e.g., for six families, lod score at theta = 0.00 of PIF/Gl is 3.58). In 107 randomly collected samples from whites, PIF is strongly associated with Db (chi 2(1) = 20.02; P less than 0.0001) and Gl (chi 2(1) = 12.58; P = 0.0005) but not with Pr, Ps, Pm, and Pa proteins. These data (probably reflecting genetic disequilibrium) suggest that PIF may be closer to Db and Gl than to other identified loci of the PPP gene complex. The PPP gene complex includes at least seven genes (and probably more) that produce many acidic and basic proline-rich proteins, constituting about two-thirds of parotid salivary proteins that are thought to have important functions at the tooth surfaces.