Mariah Carey has been riding high during her Las Vegas residency, but unfortunately, her sister Alison has been having a tough time. The 54-year-old recovering drug addict has been fighting for her life and wants her famous sister's help. 

Alison, who is aHIV-positive, has been struggling to get back on the straight and narrow as she was a victim of a home invasion attack last April, which left her brain damaged and seriously ill. Since the attack, she has been in and out of the hospital, with medical bills stacking as the months go by. Now, as she awaits further brain and spine surgery, she recorded a heartbreaking video to her iconic sister, pleading for her help.

"Mariah, I love you, and I desperately need your help," she said in the video posted by The Daily Mail. "Please don't abandon me like this."

Their brother, Morgan Carey, who admitted in the past that he and the "I'll Be There" singer have been estranged for years, hopes the video will strike a chord with Mariah and somehow even push them to make amends.

Admist it all, a representative for Mariah denies all claims that she has not helped her sister: "Through the years, Mariah has spent hundreds of thousands of dollars supporting Alison and her children," the rep told The Daily Mail Online. "In fact, Mariah has supported her extended family for over two decades."

Morgan, who currently resides in Italy, says that is all untrue, adding Mariah has not spent a dime to help out their dying sister, and he is willing to fully blame her for her plight. He even explained that her mental health is beginning to deteriorate.

"Because Mariah has not found it in her heart to help Alison get the care she requires, there are times when Alison forgets or is unable to take her medication and this sometimes precipitates problematic behavior," he said. "Alison was institutionalized for observation after being found wandering in the street barefoot and partially undressed, causing the police to be concerned."

Take a look at Alison's plea in the video, below:

Her family isn't the only one Mimi is beefing with. Watch how she threw shade — again — at Jennifer Lopez with BET Breaks, below:

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(Photos from Left: Mike Coppola/Getty Images, Messerschmidt/Splash News)