Saraga, Henoch Schonlein Purpura IGA Vasculitis in Adults is quite rare.
Was your family member diagnosed by a skin biopsy of a lesion?
What were the symptoms that manifested first? Mine was skin lesions, then GI and now kidney. Lungs can also be impacted, mine to date, are holding fine.
I want to help you as those of us who have this are few. I have resources to share.
Namely: if presented as skin lesion you need to get a biopsy taken and prepared in manner Mayo in Rochester needs it so they can diagnose one. Second, prednisone is often used and is one of the few aids. But it is a vicious drug and will cause many side effects. Shaky hands, mental/mood malabity.

What you describe sounds like the HSP IGA Vasculitis has progressed to IGA Nethropothy (sp) that is the IGA attcking the kidney.
The back pain and protein are symptoms I share.

My team includes:
Rheunatologist (auto immune), nephrologist (kidney), dermatologist (kidney), gastroenterologist (gi. My weakest link so far, still building my team), primary care doctor.

I am on a drug trial with Mayo in Florida (third patient with this disorder) to be treated in this trial. Early on the trial but my painful skin lesions have been in remission since I have been on the trial.

If your family members diagnosis is indeed HSP IGA Vasculitis. We need to connect him to Dr. Megan Sullivan, Rheumatologist (one of several Mayo team members) working my case.
Also you can reach me junetoothaker@gmail.com
Let’s try to get him to help. Or at least less impact.
June