Normal values for morphological abnormalities in school children.

Clinical morphology has proven to be a strong tool in the delineation of many syndromes and a helpful instrument in molecular studies. Numerous studies have been performed investigating the prevalence of minor anomalies in various disorders; all concluding that minor anomalies can well be utilized as indicators of altered embryonic differentiation. However, for adequate evaluation, normal values for phenotypic abnormalities are essential. So far, only few studies on the frequency of phenotypic abnormalities in the normal population have been done having one thing in common: all were performed in newborn infants. We studied morphological characteristics in a group of 1,007 school children, representative for the Dutch population, through a body surface examination using detailed definitions for all morphological findings. The region of study and distribution of children over various school types was chosen in such a way that it represented the general Dutch population. The median age of the studied children was 11 years (range 8-14 years), sex ratio (M:F) was 0.93. Nine hundred twenty-three children were of Caucasian descent, 84 others of mixed ethnic backgrounds. The reliability of the examinations was tested by independent scoring of 111 children by two observers, showing a kappa score of 0.85. Normal values for the morphological findings are presented together with their age-adjusted classification. These normal values provide a valuable source for validation of classifications of phenotypic abnormalities, especially those that are depending on frequency, that is, minor anomalies and common variants. Furthermore, they will allow a proper evaluation of patterns of phenotypic abnormalities found in patient groups with specific disorders.