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Key Terms

  1. Phenotype: all morphologic and functional attributes of an individual. The term may also refer to the organs, tissues, or cells of that individual, excluding the primary genome morphology.

  2. Genotype: primary DNA sequence of an individual. It may also refer to the organs, tissues, or cells of the individual. Includes both nuclear and mitochondrial DNA.

  3. Morphologic anomaly: macroscopic and/or microscopic anatomic phenotype representing a substantial departure from the population. A substantial departure implies that the anomaly is seen in a small fraction of the population, generally less than 2.5%. Malformations, deformations, disruptions, dysplasias, and sequences are types of morphologic anomalies. Morphologic anomalies can also be subdivided into major and minor.

    • Major morphologic anomaly: carries a significant consequence for the health or appearance of the individual.

    • Minor morphologic anomaly: carries minimal or no health consequence for the individual. However, it may have a modest impact on appearance.

    • Malformation: nonprogressive, congenital morphologic anomaly of a single organ or body part caused by alteration of a primary developmental process. Malformations typically arise during embryogenesis and are generally caused by gene mutation, teratogen exposure, or both.

    • Deformation: alteration in shape or position of a body part caused by aberrant mechanical force(s) distorting a normal structure. Deformations are causally heterogeneous and may occur as isolated phenomena or be a part of a broader malformation pattern, such as a syndrome. Deformations generally occur after organogenesis and may be seen at any time during pregnancy or postnatally. Deformations may be reversible.

    • Disruption: nonprogressive morphologic anomaly caused by breakdown of a body structure or organ with normal developmental potential.

    • Dysplasia: dynamic or ongoing alteration of cellular constitution, tissue organization, or function leading to a morphologic anomaly within a specific organ or tissue.

    • Syndrome: in dysmorphology, a syndrome represents a pattern of causally related anomalies, at least one of which is morphologic. These anomalies may not be pathogenetically related. Syndromes can be characterized by a combination of malformations, deformations, disruptions, sequences, and dysplasias. The multiple anomalies present in a syndrome are caused directly and independently by the underlying etiologic abnormality.

    • Sequence: one or more secondary morphologic anomalies that cascade from a single malformation, disruption, dysplasia, or deformation. The downstream anomalies are not necessarily directly attributable to the primary etiology.

    • Association: pattern of anomalies that occur together more often than expected by chance. At least two morphologic anomalies must be present. A causal relationship is not known.

    • Polytopic field defect: group of anomalies derived from disturbance of a single developmental field. A developmental field is a region or part of an embryo that responds as a unit to embryonic interactions, and results in complex or multiple anatomic structures.

  4. Morphologic variant: mild anatomic phenotype that represents a small departure from the appropriate reference population. A small departure implies that the anomaly is found in approximately 2.5% to 10% of the appropriate reference population.

Based partially on work by the Elements of Morphology Consortium, 2013 revision. Hennekam RC, Biesecker LG, Allanson JE, ...

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