The story of Ethan Couch, the Texas teenager who received probation in 2013 for his role in a deadly drunken-driving crash, has helped lodge the term “affluenza” securely in the American lexicon.

Its use in the courtroom, however, appears to be fairly novel.

There is little evidence before the case of Mr. Couch, 18, of defense lawyers or expert witnesses invoking the term “affluenza,” a malady said to result from excessive privilege, in bids for leniency.

Several legal experts and mental health professionals could point to no other examples, though defense lawyers have certainly argued the underlying rationale — that a child raised poorly faces special disadvantages.

“An effective criminal defense lawyer is trying to come up with an explanation for the wrongdoing that will resonate with a judge,” said Daniel Filler, a professor of law at Drexel University.