Ethnic variation in vitamin D-binding protein (GC): a review of isoelectric focusing studies in human populations

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Abstract
Since the discovery in 1977 that the GC1 gene could be resolved into two common subcomponents on an isoelectric focusing (IEF) gel, a large number of ethnic groups have been screened to analyze the extent of genetic variation in human populations. Using the IEF technique, approximately 50,000 individuals from 160 different populations have been tested for the GC polymorphism. A marked variation in common GC suballele frequencies in different geographic areas seems to correlate with skin pigmentation and intensity of sun light. Pigmented (black) and keratinized (yellowish) skin type populations have a relatively high frequency of the GC *IF allele as compared to white skin populations. By comparison non-pigmented and non-keratinized white skin populations are generally characterized by having the maximum values of the GC *IS allele. The anthropologic significance of the GC locus has been enhanced further by detecting additional unique GC variants which provide useful information about evolutionary links between different populations. However, the presence of some electrophoretically identical unique variants in genetically and geographically distinct populations demand further investigation of these allelic variants to shed more light on their origins.