RESUMO
The study aimed to carry out a comparative analysis between the lip print patterns in individuals with Down Syndrome and their nonsyndromic biological siblings. This was a cross-sectional blind study using an inductive approach and extensive direct observation procedures. A total of 68 cheiloscopic charts, named cheilograms, were divided into two groups (n=34), as follows: G1, including Down Syndrome individuals; and G2, including their nonsyndromic siblinggs. The convenience sample was selected in the city of João Pessoa, PB, Brazil. The following features were evaluated in eight labial regions called sub-quadrants: oral commissures (downturned, horizontal and upturned); lip thickness (thin, medium, thick and mixed); and labial grooves (I - complete vertical; I '- incomplete vertical; II - bifurcated; III - criss-cross; IV - reticular; or V - undefined). The data were analyzed by paired Student's t test and McNemar's Chi-square, with a 5% significance level. Most Down Syndrome individuals were found to have downturned oral commissures in 73.5% of cases, while their siblings showed a predominance of horizontal commissures in 73.5% of cases (p=0.009). There was no statistically significant difference for lip thickness between groups. In the analysis of labial groove patterns, Down Syndrome individuals (G1) showed a significant prevalence of the type I pattern (52.2%) as compared to their nonsyndromic siblings (30.1%) (p =< 0.001). Due to the tendency of having vertical labial groove patterns and downturned commissures, Down Syndrome individuals present cheiloscopic differences in relation to their nonsyndromic biological siblings, which suggests that syndromic genetics influences the development of these features. However, this may imply in a reduced potential of cheiloscopic identification due to the low divergence of labial phenotypes among Down Syndrome individuals.