Genetics and Classifications.

Arthrogryposis multiplex congenital (AMC) is a descriptive term for a group of conditions that all share the characteristic of congenital contractures. There are an estimated 400 discrete diagnoses that can lead to a child being born with arthrogryposis. The 2 biggest categories of conditions are amyoplasia and distal arthrogryposis, which combined make up ∼50% to 65% of all diagnoses within the AMC subset. Amyoplasia, the most common AMC condition, seems to be a nongenetic syndrome, leading to very characteristic upper and lower limb contractures. The distal arthrogryposes, in contrast, have an underlying genetic abnormality, which in many cases seems to target the fast twitch muscles of the developing fetus. Classifying AMC is a difficult task, given the broad range of conditions represented. Four different classification schemes are presented.