Minor anomalies: Diagnostic clues to aberrant human morphogenesis
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Assessment of the degree of fluctuating asymmetry has been used in a variety of organisms as a measure of genetic and/or environmental stresses encountered during embryonic development. However, fluctuating asymmetry has not been widely used in humans in the diagnosis of congenital anomalies. Rather, assessment of patterns of minor anomalies has been utilized to infer the degree of embryonic developmental instability accompanying either genetic or teratogenic insults.
A minor anomaly is a structural feature seen in less than 4% of the general population, which is of no cosmetic or functional significance to the affected individual. Minor anomalies may or may not have functional or diagnostic significance when taken in the context of the entire child. In dysmorphology, minor anomalies have been useful in three distinct ways. First, some minor anomalies have been external markers of specific occult major anomalies. In addition, the vast majority of malformation syndromes in clinical genetics are recognizable as patterns of minor anomalies. Finally, although 15% of normal newborns have one or more minor anomalies, the finding of three or more minor anomalies is distinctly unusual. The risk of having a major occult abnormality increases proportionately with the number of minor defects present, with three or more minor anomalies signalling a 20% risk of a major occult structural defect.
In summary, just as fluctuating asymmetry may be a marker of abnormal environmental or genetic stress in the developing embryo, the presence of minor anomalies can be utilized to assess developmental instability.
Key wordsminor anomalies dysmorphology fluctuating asymmetry birth defects
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