This is a sad story, the young man has a problem that needs therapy and management and the issue hasn't been discussed between the siblings. Someone needs to diagnose his condition and decide if the tantrums are because of anger or because of frustration with being unable to express himself or not listened to, or any number of situations and conditions. Life must be miserable for the youngster. I taught students with a wide range of abilities and conditions over 32 years and have never seen this sort of behavior.

The nephew hasn't hit puberty yet. I think now is definitely the time to express greater interest and concern.

I wrote the letter. I never did talk to my sister about her son. I remembered that in the past, even when she asked for advice/suggestions/opinions, she really didn't want it – she would get angry/upset/hurt if people didn't agree with her. I thought that I'd have better luck talking to our mother about my concerns. Unfortunately, our mother wasn't open to discussing my nephew's “different” behaviors. She was so upset; she wouldn't let me talk.
My mother did say my sister had asked a teacher if her son was doing anything – and the answer was no. But, my nephew appears to be a lot like my sister at that age; ok in a supervised environment, but has issues otherwise. (I genuinely believe my mother & my sister didn't perceive his odd behaviors as odd. After all, it is his normal.)
I wish I could have let my sister know that the barking sound her son makes is the same noise she made as a pre-teen/early teen. The last time I saw him, my nephew “zoned out” while I was talking to him; he didn't appear to be mentally present in the room – just like she used to do.

And, I wish we could have discussed his skewed concept of reality. One of the triggers for his anger is when he doesn't get what he wants, even if it was pure chance. And he seems to need to blame someone or be angry at someone because of it. For example; we'd been playing a game & everyone was having a good time - until he didn't get the roll he wanted. He went from laughing to ballistic in an instant (he was 10, it happens). But, he accused us of “doing something to the dice” and he truly believed it. He had none of the signs kids normally have when they know they are lying. This sort of thing seemed to be standard behavior for him: laughing one minute, crying & accusing others of doing something or being mean to him the next. In reality, nothing actually happened.

Hi- this is for the lw. I'm not a shrink but I've both seen
& experienced a lot of mental illnesses in my life. He sounds like
He is bipolar & autistic. I am bipolar- the fast changing
Moods (they call it rapid cycling) I was already was on
Medication by the time I was his age because
My parents took me to a dr for help as soon
As they realized I was having problems. The
Weird noises & abnormal talking is autism- my
9 year old daughter is high functioning autistic
(asperger's). It's a shame they don't get him help
Because with the medicine they have now...well
It is incredible. Completely works. He could lead
A totally different life. I am a strong advocate for
Psychotropic medication.