Effects of age and sex on taste sensitivity to phenylthiocarbamide (PTC) in the Berkeley Guidance sample

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Abstract
Using a modification of the Harris and Kalmus method for ascertaining the taste threshold for phenylthiocarbamide (PTC), data were collected on 424 Caucasian individuals from the three generational longitudinal study of the Berkeley Guidance subjects in Berkeley, CA. Analysis of the data indicates the distribution of thresholds is significantly different from that in the London sample of Harris and Kalmus in that the frequency of nontasters is about half that found in London. The difference is not attributed to the modifications made in the testing procedure but to a real difference in gene frequency. Both the PTC taster and nontaster phenotypes display a large amount of variation in expression between individuals. They are differently expressed in males and females, the latter being more sensitive. As people age, the expressions of their genotypes change. Neither age nor sex seem to affect the penetrance of the PTC genes which remains the same within each sex at all ages unless some other environmental factor, such as radiation, impinges. Consideration of these relationships is necessary for the investigation of family relationships, the mechanisms responsible for maintaining this ancient genetic polymorphism and the degree of polytypy present in the species.