Hi, A Few Weeks Back A Urine Sample Revealed Blood

Hi, A few weeks back a urine sample revealed blood content. I saw a urologist. After checking my prostate a cat scan was done. I also yesterday had a cystoscopy performed. Everything checked out normal. Even though he said it is never normal to show blood in your urine test he had no explanation. I then offered one from my mom. She said to tell him it runs in the family. My mom started showing it at around 50. She is now 71. My baby sister first showed it in 2nd grade after an exam. My mother would not let them test further saying it was hereditary. My sister is now 36. My mom is one of 6. Four of the six show it. So did her dad.Her one sister also first showed it also as a child and she just turned 82. I also have at least 9 out of 28 first cousins who show it. None of us have any other health issues. Is it possible to have a hereditary condition like this? If so,what is it called? My doctor still maintains it is not normal but i heard the only thing left to do would take a sample of the kidney and biopsy it. It is an invasive test that nobody in the family ever got and we all are otherwise very healthy. thanks for your time