The older one has a diagnosis, but the parents suspected it from about age 11. Bright girl, top sets, very hard working, compliant, polite, obedient, etc, but always said whatever will get the best reaction at the time, no concern about whether it was the truth or not, and no concern how long it would take to be found out. For example, came home with report card, told parents about top exam results, lots of praise, reward, etc - asked for money, got money - report card did not show the results she said she had, which became apparent when parents opened it a few minutes later, by which time money was in her hand and she was out the door.... It is hard to describe but she lied to get an advantage, even if the advantage was only for a few minutes, no concern about consequences later at all. She also put her baby brother on the outside window sill. And killed a chicken by kicking it to death, an put it back in its cage and said it was fine - clearly visible on CCTV killing it. Stole from parents, eventually attacked mother and beat her until she handed over her bank card. Anyway, parents knew something was seriously wrong from about 11, their second and third children are normal, and their fourth child is worse, still only 15, no diagnosis.
But the first child is doing better now, has made the decision to conform to society, and earn their living - highly intelligent but no qualifications, did in fact eat a GCSE paper sitting in the exam.... but after a few years of heavy drinking and crime changed their mind about wanting to live like that, got an apprenticeship, and progressing very fast up career ladder
She has always been nice to be with in a strange way, even if you were afraid of being pick pocketed, and not sure if you were being lied to. Now says she wants to do well, and I hope she means it. I enjoy her company but still wouldn't have her in my house.
The parents very firmly vetoed babysitting though, and probably still would if they heard of it. ( child is in their 20s)