Complement 3 glomerulopathy (C3G) is a group of rare kidney diseases characterized by protein buildup in the kidneys. This condition affects about 1 to 2 per million people worldwide. Here are 10 symptoms—including swelling and blood in urine—that could indicate that someone has C3G.
C3G is a rare disease that occurs when the complement system (part of the immune system) becomes overactive. That causes the body to make too many C3 proteins, which can injure the glomeruli, or the kidneys’ filtering system.
This causes a number of symptoms, including blood in urine (hematuria). Damaged glomeruli can leak red blood cells, changing the color of urine from yellow to pink, brown, or red.
See your healthcare provider right away if you notice blood in your urine so they can investigate the cause.
In addition to blood in the urine, people with C3G usually experience high levels of protein in their urine (which is called proteinuria). That’s because their kidneys’ filtering system isn’t working properly, and it allows proteins to pass into the urine.
Urine that contains too much protein usually appears dark and foamy.
The kidneys’ primary job is filtering waste and extra fluids from the blood, and creating urine to excrete them.
When the kidneys are damaged by C3G, they pass a protein called albumin into the urine so there isn’t enough of it in the bloodstream. When people have low albumin levels, water leaks into their tissues, causing swelling. This swelling usually happens around the feet and ankles, though it can appear in many parts of the body.
Swelling can get worse over time as C3G continues to damage the kidneys. The body continues to hold on to more sodium and water, leading to further swelling.
There are medications available to relieve swelling and prevent fluid overload.
When C3G progresses to an advanced stage, it can result in less urine output (oliguria). Because they kidneys are damaged, they cannot produce urine as they normally would.
Less urine output usually causes too much fluid to build up in the body, leading to swelling, high blood pressure, drowsiness, and possible kidney failure.
High blood pressure (hypertenstion) is a common sign of kidney issues, including C3G.
Damaged kidneys cannot filter and remove extra fluid from the body. This extra fluid increases the pressure or force within the arteries, leading to hypertension.
High blood pressure is a serious condition that raises the risk of heart disease and kidney failure. So if you have C3G, your healthcare team will likely check your blood pressure regularly and may prescribe hypertension medications such as ACE inhibitors and ARBs.
Fatigue is a commonly-reported symptom of C3G. A 2024 study found that of the participants with C3G, 77% reported needing to sleep during the day due to fatigue.
With C3G, the damaged kidneys cannot effectively remove waste from the bloodstream. The buildup of this waste can affect the brain, and people with the condition may notice daytime fatigue and trouble concentrating.
Let your healthcare team know right away if you experience any changes in your mood or ability to think.
In people with C3G, the complement system, which is part of the immune system, is overactive and sends out infection-fighting C3 proteins when it shouldn’t. That means when the body actually encounters a dangerous virus or bacteria, the immune system doesn’t have enough proteins to fight the infection.
As a result, people with C3G are at an increased risk of infection and often experience frequent infections.
Having C3G may affect your vision over time.
Specifically, people with C3G are at increased risk of drusen, a type of eye condition that occurs when complement system proteins and fats accumulate in the back of the eye. These yellow-colored deposits can distort or blur vision, particularly as people get older.
Though it’s uncommon, C3G may affect how fat is distributed around the body, particularly for people who have dense deposit disease, one of the specific types of C3G.
Uneven fat distribution, known as acquired partial lipodystrophy, occurs when the body cannot effectively use and store fat. Some areas of the body may appear thin where there’s a lack of fatty tissue, while other areas of the body seem larger due to the accumulation of fat.
In C3G specifically, patients usually have reduced fat tissue in their upper bodies. Experts believe this could be because the complement system is involved in the growth of fat cells.
People with C3G and chronic kidney disease are at an increased risk of developing gout.
Gout is a chronic condition that occurs when there is too much uric acid—a waste product—in the blood. When kidneys are damaged and unable to filter uric acid out of the blood, it builds up and settles in the joints.
Uric acid can form crystals, which causes severe pain in the joints. It most often occurs in the big toe.
Researchers are still learning more about what causes C3G—it’s been linked to genetic changes or sometimes infections.
There is no cure for C3G, but many of the symptoms can be managed with blood pressure drugs, medications that suppress the immune system, therapies to target the complement system, and more.
Lifestyle and diet changes can also help manage high blood pressure and maintain better kidney function, including:
- Limiting your intake of sodium
- Avoiding tobacco smoke
- Maintaining a healthy weight
- Getting 30 minutes of physical activity most days
- Prioritizing quality sleep for 7 to 8 hours each night
- Practicing stress management techniques
