I have written several posts on this blog about Parental Alienation Syndrome, such as here,here, and here. To get another lawyer's take on this subject, I present the following article published by Dan Nunley at the Oklahoma Family Law Blog a few months ago:
Statistics show that approximately one in two marriages end in divorce and about ten percent of those divorces involve child custody battles. During these emotionally charged proceedings, some children exhibit emotional detachment from one or both parents. The cause of this emotional detachment is unknown and the issues involved are complex.
One suggested theory, developed by the late Richard A. Gardner, M.D., has come to be known as “Parental Alienation Syndrome” (PAS). PAS typically portrays one parent as an evil alienator who through consistent brainwashing is responsible for turning an impressionable and vulnerable child against the innocent, enstranged parent. As a result of this brainwashing, the child reflexively supports the alienating parent and experiences no guilt over their own cruelty towards the enstranged parent.
PAS is becoming an issue in more and more custody cases. However, the mental health profession is far from agreement about the existence of the syndrome. Noting the lack of supporting data, the American Psychological Association has “no official position on the purported syndrome,” according to its statement on PAS.
The legal community is divided as well. While many family lawyers believe the syndrome is a legitimate psychological diagnosis, others view it as nonsense. They say it's used primarily by parents who want someone to blame for their poor relationship with their children.
Read more about PAS in this recent article from Lawyers Weekly USA.