To determine whether the Agouti Signalling Protein (ASP) gene is associated with 
skin and hair coloration in humans, the complete coding region of ASP was 
screened for polymorphisms. Analysis of ASP in Caucasian, African-American, 
Spanish Basque, Hispanic, Apache and Australian Aboriginal populations revealed 
no amino acid substitutions. A single polymorphism in the 3' untranslated region 
occurred at a frequency of 0.2 in African-Americans. Variants of the 
Melanocortin 1 Receptor (MC1R) gene have been found to be associated with red 
hair and fair skin in humans. Red hair individuals are usually compound 
heterozygotes or homozygous for one of a number of MC1R polymorphisms associated 
with red hair. Some individuals however are heterozygous for only one of these 
polymorphisms and dizygotic twins can be concordant for MC1R variants but 
discordant for hair colour. A recent study has also identified rare redheads 
carrying no MC1R variants indicating that polymorphisms of the human MC1R gene 
are required but not sufficient for the red hair phenotype. To address the 
question of whether ASP also contributes to the red hair phenotype, individuals 
previously identified as having unexpected MC1R genotypes were screened for 
polymorphisms at the ASP locus. No polymorphisms were found in any of these 
individuals. Results indicate that the human ASP gene is unlikely to function in 
normal human pigmentation in the same way as MC1R.