1. Birth defects can be placed into one of the following established categories:
• Deformation. Deformation anomalies have no inherent genetic basis. Rather
mechanical forces have altered the shape of the structure. Talipes equinovarus, or
clubfoot, is the classic example of a deformation. Although the lower limbs were
genetically programmed to form normally, external forces (such as a decreased
amount of amniotic fluid) or internal forces (such as neurological impairment)
prevented such development.
• Disruption. Like deformation, the genetic program of the structure in disruption
was normal. However, the normal developmental process was interrupted by some
mechanism, causing the anomaly. Examples of disruption are the anomalies
observed in newborns exposed to cocaine in utero. This drug a known
vasoconstrictive agent. Is believed to cause malformations ranging from intestinal
atresias to craniofacial structures by temporary restricting blood supply to the
developing structures.
• Dysplasia. Dysplasia refers to a general abnormality at the level of cellular
organization in a specific tissue. One example would be a connective tissue disorder,
such as Marfan’s syndrome
• Malformation. A malformation is an anomaly in which the developmental process
was abnormal from the outset. An example is a cleft lip and palate. In which the
structures that joint the lip and palate do not fuse normally. In general
malformations are caused by a genetic mutation, congenital infection, teratogen
exposure.
• Syndrome. A child will often have multiple malformations and it is important to
determine their relationship. In a syndrome the observed malformations are
pathogenetically related to a single cause. For example in Marfan’s syndrome, the
tall stature, dilated aortic roor, loose joints, and lens dislocations are all caused by
an abnormality in fibrillin.
• Association. An association is the nonrandom occurrence of a set of malformations
that are not pathogenetically related. VATER or VACTERL – vertebrae,
imperforate anus, cardiac anomalies, TEF, renal anomalies, limb anomalies (radial
defect). Although these anomalies occur more frequently together than they do
separately, they are not believed to be casually related. That is, they are not caused
by the same genetic or teratogenic origin.
• Field defect. A field defect is a set of malformations that are grouped in a located
area of a body or a so-called developmental field. Abnormal developmental stimuli,
such those caused by a teratogen or a mutated gene result in a developmental field
defect. One example is a cloacal extrophy.
• Sequence. Sequence is a series of findings that are derived from a single anomaly or
mechanical force. One example is Pier Robin sequence – the constellation of a small
jaw, a midline U-shaped cleft palate and relatively large and protruding tongue. The
primary anomaly is the small jaw, which fails to provide an adequate room for the
tongue and displaces it in a superior direction. The tongue then prevents closure of
the palatine shelves, causing the cleft palate. It is important to mention that the
borders of these definitions are not firm, and overlap does occur. F.e. P-R syndrome
can be an isolated findings or a feature of several genetic syndromes.