I sat in an audience of about 500 other nephrologists learning the latest about diseases affecting the filtering parts of the kidney, the glomeruli, and their treatments. It was the second day of the American Society of Nephrology Kidney Week and the end of a very long day of lectures that would be capped off with a discussion of case studies, led by experts in diseases of the glomeruli, the answers unknown to them and us. A pathologist stood at the podium and described a case of a 47 year-old Black woman who had donated a kidney 5 years ago. She was a little older and I had donated a bit longer ago, but I was particularly intrigued, the story hitting so close to home.
Her creatinine test for kidney function was normal, but she had 2,000 milligrams of protein in her urine when less than 30 milligrams was normal. Her blood level of albumin, a kind of protein, was low—2.3 when normal is closer to 4.
She was already on the heavy side when she donated, with a body mass index (BMI) of 28 and she had only gotten fatter with time. If she were my height then she would be about 20 pounds heavier than I am now and had gained another 30 over the last 5 years, giving her a BMI of 33.
I stared at the screen to consider which of the 4 options staring back at me that could be causing her kidney problem and translated them in my head. Was it:
A. Secondary FSGS due to obesity?… Scarring of the kidney filters caused from being too fat?
B. Primary FSGS due to APOL1?… Scarring of the kidney filters caused by an abnormal gene found in some Black people?
C. Membranous nephropathy?... Clumps of antibodies bound to antigens deposited in the kidney filters’ lining
D. Something else that I dismissed so quickly because it so obviously not the answer, that I can’t even remember what it was now.
I thought about what was taught over the past 6 hours and remembered one of the experts saying how a very low albumin was a sign of a problem affecting the entire body. I remembered membranous nephropathy. While the reason why the body begins to make antibodies against itself, the disease can be caused by many things affecting the body, like different drugs, infections, or cancer.
C, I decided and pressed the button on the remote device in my hand with a reasonable level of confidence and 6 of the 10 alloted seconds to spare. When the timer reached zero, the screen flashed the results. A minority of my colleagues in the audience agreed with me. Only about 20%. A handful chose D. And the remaining 75% were divided between A and B.
I was eager to hear what the expert panelists would say. They discussed what stood out for them in the case. She had a lot of protein in her urine. She only had one kidney. She was Black. She was fat. They debated whether or not they would risk a biopsy, pushing a hollowed out needle into her one kidney to get a sample to confirm the diagnosis. They hemmed. They hawed.
“There is a lot of obesity in this country, but I can’t say I see much FSGS because of it,” said one.
“Oh I see plenty,” scoffed the other.
And she is Black. They could agree there.
A mutation in the APOL1 gene evolved as Nature’s response to the deadly sleeping sickness caused by the tsetse fly of Sub-Saharan Africa. One who had a copy of the APOL1 variant were more likely to survive—and pass on the gene to their offsprings. The unlucky one who inherited a copy from each parent was much more likely to develop FSGS someday. Researchers estimate that half of African Americans have at least one copy of the gene variant.
“I think it’s either A or B,” said one.
“I would have to agree,” conceded the other.
The colleague leading the discussion nodded slowly with a slight tilt of his head that read disappointment to me. He advanced his slides to project an image of the fat Black woman’s kidney on the screen and reviewed its findings. Findings characteristic of C, membranous nephropathy.
A brief hush fell over the experts and crowd. Then the conversation rolled on with the next slide asking what medications we would use to treat this patient.
At the end of the session, I thought about going to the microphone stand in the aisle to ask why the experts had not seriously considered option C given the low albumin… and that obesity can on rarely be confirmed as the cause of FSGS…and that only an estimated 13% of African Americans have 2 copies of gene variant… and that only a small percentage of those who have 2 copies actually develop FSGS…and that about 20 other gene mutations not specific to Black people can cause it too. But I didn’t go to the microphone. I already knew the answer.