Schizotypal personality disorder and the insanity defense

What constitutes a "mental disorder" for purposes of the insanity defense? Does mental disorder denote any diagnosable condition listed in the third edition of the Diagnostic and Statistical Manual of Mental Disorders? Is a mental disorder a disturbance wherein the functional criteria of the appropriate insanity law appear to be met? Or does insanity law define mental disorder apart from functional criteria of insanity? The answer to the last question is that some insanity laws attempt to define or qualify mental disorder, but many do not. Unclarities in the law leave room for unnecessary disagreements between expert witnesses even before the functional criteria for insanity are to be addressed. The potential for confusion is compounded when the defendant's disturbance is ambiguous, amphibious, or both. Schizotypal personality disorder is offered as an example of such a disturbance, and inferences are discussed.