Any unusual variation or abnormality in the shape, structure, and/or function of an organ, body part, or tissue is commonly referred to as a birth defect. However, congenital anomaly is the more accurate and preferred term, since birth defect can be misinterpreted to mean a defect produced by the birthing process. Congenital anomalies may be external or internal, single (isolated) or multiple, major or minor, and by definition are present at (and almost always before) birth, although in some cases detection/diagnosis occurs well after birth. As a group, congenital anomalies are common, have a wide range of clinical severity, and can develop, in one form or another, in any anatomical structure or location. There are many different causes of congenital anomalies, known and unknown, but in terms of how they develop, there are four major types: malformations, deformations, disruptions, and dysplasias.
Variation among individuals in physical characteristics, both external and internal, is an essential attribute of any organism that reproduces sexually, including humans. Although less obvious, but no less important, people also differ in their metabolism and other cellular/chemical processes that help form and maintain the body. The process of normal development in the body is called morphogenesis, while abnormal development is known as dysmorphogenesis. Dysmorphology, then, is the study of congenital anomalies, including their formation, causes, and patterns of occurrence.
An important task, in both medical and sociocultural contexts, lies in determining what constitutes a congenital anomaly, and what qualifies as an accepted morphological variant. Further, what distinguishes a major anomaly from a minor one? In other words, what is normal, and what is abnormal? In some cases, the distinction is obvious, in others it is not. Terms such as normal and abnormal are generally agreed to be subjective, and thus not applicable when applied to individuals in a broad context. The same can be said of terms such as defective, anomalous, deformed, malformed, aberrant, irregular, and the like. Even though some terms and phrases are perceived as subjective, negative, and offensive when misapplied as generalities, they are nonetheless necessary in a medical context. With due sensitivity and care, these same terms can be used clinically in an objective and instructive manner.
Compared with the complex and evolving social issues of perception and acceptance, the medical approach to distinguishing normal variants from minor and major anomalies is more objective and direct. Regardless of the anatomical structure or process, the primary criterion involves evaluating whether its function, shape, structure, and/or size fall within or outside the normal (expected) range. To help answer that question, measurements of every conceivable type have been taken and catalogued over the years on countless individuals. Statistical formulas are applied to the data for a given characteristic or function (e.g., height, weight, blood pressure, serum enzyme levels, etc.) to determine its normal range. If needed, adjustments for age, gender, race, ethnicity, and many other variables can also be made. The results are often graphed and, for most human characteristics, a line drawn through the data points on the graph produces the famous bell curve, a name derived from its shape. Calculations based on such factors as the total number of individuals studied and the range of measurements obtained, among others, are used to mark off a section in the middle of the curve, such that most individuals (usually between 80% and 95%) fall within that range. Therefore, any values above or below (i.e., outside) that range are considered anomalous or abnormal. Measured values for minor anomalies might fall several percentage points on either side of the upper and lower boundaries of the normal range, while major anomalies lie at the ends of the curve.
Among other new challenges, parents and families of children with congenital anomalies are exposed to a bewildering array of new medical terms and phrases, and asked to understand, process, and remember these while likely under a great deal of stress. The practice of medical genetics consists primarily of communicating with individuals and families about difficult and complex issues. Geneticists and genetics counselors are especially sensitive to the psychosocial impact terminology can have on perception and understanding of congenital anomalies/genetic disorders. Parents of a newly diagnosed child inevitably want to know how the anomaly or genetic syndrome occurred. An understanding of the different types of anomalies is the basis for answering that question.
Scott J. Polzin MS, Thomson Gale, Gale, Detroit,