Inter-relation between variables determining constitutional UV sensitivity in Caucasian children

Sensitivity to ultraviolet (UV) light is associated with phenotypic variables like iris or hair colour or freckling, which are all strongly inter-related. We assessed the pattern of association among these factors to construct a summary measure reflecting constitutional UV sensitivity in a simple one-dimensional score with sufficient discriminating power.

Information on iris and hair colour (3 and 4 categories, respectively), freckling (none vs. any) and the reaction to mid-day summer sunlight as an outcome (dichotomized into 'burn' and 'tan') was collected in a cross-sectional study among children at school enrollment in 1999 and 2000 in Göttingen, Germany (n=3765 with complete data). Chi-squared automatic interaction detector (CHAID) analysis and log-linear modelling was used to assess the pattern of mutual inter-relations.

Hair colour turned out to be the factor most strongly associated with UV sensitivity. In case of blonde or brown hair (the most common phenotypes in our sample), the consideration of freckling further refined the classification system, whereas iris colour did not contribute additional information. The results of the CHAID and log-linear analyses suggest a simple five-point score capturing constitutional UV sensitivity. The discriminating power of this score was high in our sample, with the proportion of persons who burned ranging from 7.7 (lowest category) to 73% (highest category).

The new scoring system summarized efficiently relevant information on individual constitutional UV sensitivity in our sample. Its further validation in independent studies comprising Caucasian children or adults is necessary to assess objectively its properties for future applications.