Malformation

A malformation is a primary structural defect occurring during
the development of an organ or tissue. Most malformations have
occurred by 8 weeks of gestation. An isolated malformation, such
as cleft lip and palate, congenital heart disease or pyloric
stenosis, can occur in an otherwise normal child. Most single
malformations are inherited as polygenic traits with a fairly low
risk of recurrence, and corrective surgery is often successful.
Multiple malformation syndromes comprise defects in two or
more systems and many are associated with mental retardation.
The risk of recurrence is determined by the aetiology, which may
be chromosomal, teratogenic, due to a single gene, or unknown.
Minor anomalies are those that cause no significant physical or
functional effect and can be regarded as normal variants if they
affect more than 4% of the population. The presence of two or
more minor anomalies indicates an increased likelihood of a
major anomaly being present.