Home > Encyclopedia of Genetic Disorders > Acardia

Definition

Acardia is a very rare, serious malformation that occurs almost exclusively in monozygous twins (twins developing from a single egg). This condition results from artery to artery connections in the placenta causing a physically normal fetus to circulate blood for both itself and a severely malformed fetus whose heart regresses or is overtaken by the pump twin's heart.

Description

Acardia was first described in the sixteenth century. Early references refer to acardia as chorioangiopagus parasiticus. It is now also called twin reversed arterial perfusion sequence, or TRAP sequence.

Mechanism

Acardia is the most extreme form of twin-twin transfusion syndrome. Twin-twin transfusion syndrome is a...