Discuss as:

Judge allows defense to argue Jerry Sandusky has psychiatric disorder

Prosecutors concluded their case Thursday in Jerry Sandusky's child sexual abuse trial. NBC's Michael Isikoff reports from Bellefonte, Pa..

Jerry Sandusky's defense will be allowed to call an expert witness to testify that some of his behavior and letters to young boys are manifestations of a personality disorder and not evidence that he was "grooming" the boys for sex, the judge in his child sexual abuse trial ruled Friday.

Follow M. Alex Johnson on Twitter and Facebook.

Sandusky, 68, the former longtime defensive coordinator for Penn State University's football team, is on trial on 52 counts alleging that he abused 10 boys over 15 years. Two grand jury reports accused him of having used his connection to one of the nation's premier college football programs to "groom" the boys, whom he met through his Second Mile charity for troubled children, for sexual relationships. He has denied all charges.

Defense lawyers this week filed a motion seeking permission to introduce expert testimony from a psychologist that Sandusky has "histrionic personality disorder."

Histrionic means "dramatic" or "theatrical." People with the disorder desperately seek the approval of others and behave dramatically or inappropriately to get attention, according to the Cleveland Clinic, one of the nation's leading medical centers.

Does it matter if Sandusky has a personality disorder?

Jurors have long weekend to consider graphic evidence against Jerry Sandusky

Analysis: Prosecution presented strong case against Jerry Sandusky

The motion, which was filed Monday in Centre County Court in Bellefonte, Pa., says the testimony would offer a "fair explanation of these letters that is consistent with innocence."

"The jury should not be mislead (sic) into believing these statements and actions are likely grooming when hey (sic) are just as likely or more likely Histrionic in origin," it says.

Read the full defense motion (.pdf)

Judge John Cleland ordered that Sandusky would also have to be available for a psychiatric examination by a prosecution expert. It wasn't immediately clear whether the examination would delay the trial, but as of late Friday afternoon, court was still scheduled to resume Monday at 9 a.m. ET after prosecutors presented their case this week.

More content from msnbc.com and NBC News:

Follow US News on msnbc.com on Twitter and Facebook