Congenital Upper Limb Anomalies 175mutations, particularly in the fibroblast growth factor receptor family (FGFRs)
(Crow, 2000).
Epigenetic/Environmental
There is a widely accepted notion that “we are products of our
environment.” The same holds true for a developing embryo in the womb.
This is most clearly seen in Barker’s hypothesis, also known as Fetal
Programming (Barker, 1990). Fetal programming is an emerging concept that
links environmental conditions during embryonic and fetal development with
risk of diseases later in life.
Studies on fetal programming have mainly focused on healthy weight
maintenance during gestation as a means of lowering adverse risks in infants
such as chronic conditions in adulthood - obesity, diabetes, and cardiovascular
disease. Other factors termed teratogens, such as maternal age, infection, drugs
(pharmaceutical or recreational) may also play a role in fetal programming and
have been linked to birth defects including CULA.
Teratogens
Prenatal exposure to a teratogenic agent accounts for approximately 10%
of all birth defects (O’Rahilly and Müller, 2001). A teratogen refers to any
agent that can induce or increase the incidence of congenital anomalies and
includes radiation, infections, drugs and other chemicals. Many of these
harmful agents cause damage only if exposure occurs during a sensitive period
of prenatal development. In other words, the susceptibility of an embryo to a
teratogen may depend on the stage of development. Furthermore, the organs
undergoing the most rapid proliferation, differentiation or migration during
exposure are the most vulnerable to the influence of the teratogen. The amount
(dosage) and length of time of exposure to a teratogen are critical factors that
influence the degree of harm the agent will cause. In general, the higher the
dosage of teratogen the more deleterious the effects on the embryo. Prolonged
exposure, even at low doses can cause cumulative harm.