DSM-IV* (1994) defines Reactive Attachment Disorder (RAD) as markedly disturbed and developmentally inappropriate social relatedness in most contexts, beginning before age five, as evidenced by either:  

Inhibited Type: persistent failure to initiate or respond in a developmentally appropriate fashion to most social interactions, as manifest by excessively inhibited, hypervigilant, or highly ambivalent and contradictory responses (e.g., responds to caregivers with approach, avoidance, and resistance to comforting, or frozen watchfulness),or

Disinhibited Type: diffuse attachments as manifest by indiscriminate sociability with marked inability to exhibit appropriate selective attachments (e.g., excessive familiarity with relative strangers or lack of selectability of attachment figures)  

A report from a foster parent:  

"My inquiry about the use of RAD (Reactive Attachment Disorder) in a false allegation defense stems from a false allegation brought against an adoptive father and his biological son by two sibling adopted sisters (teens) who had been diagnosed as RAD prior to their adoption three years ago.

"My wife and I have been therapeutic foster parents since 1987, working with a large number of emotionally handicapped children.  From what we have witnessed, the RAD (Disinhibited Type) children are the most likely to make false allegations.

"CPS and Police investigators who are unaware of a child's RAD diagonosis and who ask leading questions tend to feed right into the RAD child's fantasy allegation.  I would like to see a formal study done on children who have made false allegations to see how many are RAD affected.

"One particular point about RAD children:  They will most often turn on the caregiver they have become closest to.

"I am strongly recommending that defense teams dealing with false allegations consider the possibility of RAD even if it hasn't been formally diagnosed.  It at least becomes another defense in the limited arsenal victims of false allegations have to use."
 

References (source Serwind Netzler)