Pathological expressions of dynamic shaping in pre-natal development

Certain pathological conditions of infancy find their roots in altered 'shaping' of pre-natal behaviours. Arthrogryposis Multiplex Congenita (AMC) is one such condition. Infants with AMC are born with multiple contractures of varying severity.

AMC has been related to multiple causes. The final common pathway, however, is a selective loss of anterior horn cells that result in reduced strength and frequency of movement. This creates a viscious circle in that the paucity of movement tends to lead to a decrease in the production of amniotic fluid which increases the resistance of extra-embryonic membranes to the fetus' already weakened movements. The net result is the absence of repetitive stretch that is necessary to trigger the adaptation in the mechanical properties of the developing muscles: increase in number and length of sarcomeres. AMC can severely impair the course of post-natal development.

In similar fashion, a stroke sustained early in pre-natal development will alter the fetus' pre-natal experience, often disrupting the organization of the behaviours that are necessary to support the transition from pre- to post-natal development.

Agents external to the fetus can also alter the course of pre-natal development: pre-natal exposure to ethanol is a frequent example.