Measurements in Dysmorphology and Clinical Genetics

The human body is expected to grow predictably and proportionately. The relationship of measurements to each other is expected to be constant at specific ages. These relationships can be expressed as ratios, as an index, or by the use of regression techniques. Those in common use are the relationship between height and weight. They are mainly corrected with the chronological age or the bone age of the patient. These proportions and relationships change dramatically from the fetal period through childhood to adolescence because of various interactions among genetic, hormonal, and environmental factors.

In the study of syndromes with dysmorphic features, we are looking for recognizable signs that help to define and delineate the specific condition. Those recognizable features may be quite different during different life periods. Using Down syndrome as an example, from embryofetal pathology we have learned that manifestation of the Down syndrome phenotype in a fetus depends on the gestational week, and often very few features are present until near birth. Similarly, there is a changing phenotype during childhood and into adulthood, with the typical phenotype of Down syndrome sometimes becoming hard to recognize in the adult.

Because of the change in physical appearance and therefore in the pattern of measurements with time, we can expect that some diseases or disorders will be more obvious and more easily recognized during certain stages of development. The patterns of relative measurements may partly relate to the growth spurts that occur in different organ systems at different times. Theoretically they reflect secondary and tertiary effects of the basic process and underlying pathogenesis.

Measurements of individual body parts can never be separated from general clinical impression or "gestalt." This type of general impression of the patient will usually be obtained by observing the patient for a while before taking specific measurements. The specific measurements and general clinical impression should be integrated with additional factors such as the movement pattern, mode of communication, and type of developmental disability into an overall description and impression.

There is a tendency to neglect the observation and description of the adult patient with malformations, in specific syndromes or even isolated mental retardation. As a consequence, we have limited knowledge of physical changes in syndromes with dysmorphic features as related to the aging process. Study of the natural history of these relationships may lead to a better understanding of the underlying pathophysiology and natural history of the disorders.

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