C3 glomerulopathy

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

C3 glomerulopathy is a group of related conditions that cause the kidneys to malfunction. The major features of C3 glomerulopathy include high levels of protein in the urine (proteinuria), blood in the urine (hematuria), reduced amounts of urine, low levels of protein in the blood, and swelling in many areas of the body. Affected individuals may have particularly low levels of a protein called complement component 3 (or C3) in the blood.

The kidney problems associated with C3 glomerulopathy tend to worsen over time. About half of affected individuals develop end-stage renal disease (ESRD) within 10 years after their diagnosis. ESRD is a life-threatening condition that prevents the kidneys from filtering fluids and waste products from the body effectively.

Researchers have identified two major forms of C3 glomerulopathy: dense deposit disease and C3 glomerulonephritis. Although the two disorders cause similar kidney problems, the features of dense deposit disease tend to appear earlier than those of C3 glomerulonephritis, usually in adolescence. However, the signs and symptoms of either disease may not begin until adulthood.

One of the two forms of C3 glomerulopathy, dense deposit disease, can also be associated with other conditions unrelated to kidney function. For example, people with dense deposit disease may have acquired partial lipodystrophy, a condition characterized by a lack of fatty (adipose) tissue under the skin in the upper part of the body. Additionally, some people with dense deposit disease develop a buildup of yellowish deposits called drusen in the light-sensitive tissue at the back of the eye (the retina). These deposits usually appear in childhood or adolescence and can cause vision problems later in life.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

C3 glomerulopathy is associated with changes in many genes. Most of these genes provide instructions for making proteins that help regulate a part of the body's immune response known as the complement system. This system is a group of proteins that work together to destroy foreign invaders (such as bacteria and viruses), trigger inflammation, and remove debris from cells and tissues. The complement system must be carefully regulated so it targets only unwanted materials and does not damage the body's healthy cells.

A specific mutation in one of the complement system-related genes, CFHR5, has been found to cause C3 glomerulopathy in people from the Mediterranean island of Cyprus. Mutation in the C3 and CFH genes, as well as other complement system-related genes, have been found to cause the condition in other populations. The known mutations account for only a small percentage of all cases of C3 glomerulopathy. In most cases, the cause of the condition is unknown.

Several normal variants (polymorphisms) in complement system-related genes are associated with an increased likelihood of developing C3 glomerulopathy. In some cases, the increased risk is related to a group of specific variants in several genes, a combination known as a C3 glomerulopathy at-risk haplotype. While these polymorphisms increase the risk of C3 glomerulopathy, many people who inherit these genetic changes will never develop the condition.

The genetic changes related to C3 glomerulopathy "turn up," or increase the activation of, the complement system. The overactive system damages structures called glomeruli in the kidneys. These structures are clusters of tiny blood vessels that help filter waste products from the blood. Damage to glomeruli prevents the kidneys from filtering waste products normally and can lead to ESRD. Studies suggest that uncontrolled activation of the complement system also causes the other health problems that can occur with dense deposit disease, including acquired partial lipodystrophy and a buildup of drusen in the retina. Researchers are working to determine how these associated health problems are related to overactivity of the complement system.

Studies suggest that C3 glomerulopathy can also result from the presence of specialized proteins called autoantibodies. Autoantibodies cause the condition by altering the activity of proteins involved in regulating the complement system.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

Most cases of C3 glomerulopathy are sporadic, which means they occur in people with no history of the disorder in their family. Only a few reported families have had more than one family member with C3 glomerulopathy. However, many affected people have had close relatives with autoimmune diseases, which occur when the immune system malfunctions and attacks the body's tissues and organs. The connection between C3 glomerulopathy and autoimmune diseases is not fully understood.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

C3 glomerulopathy is very rare, affecting 1 to 2 per million people worldwide. It is equally common in men and women.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Hematuria · Very frequent (99-80%)

The presence of blood in the urine. Hematuria may be gross hematuria (visible to the naked eye) or microscopic hematuria (detected by dipstick or microscopic examination of the urine).

C3 nephritic factor positivity · Frequent (79-30%)

The presence of autoantibodies (immunoglobulins) in the serum that react against C3 convertase (C3bBb).

Chronic kidney disease · Frequent (79-30%)

Functional anomaly of the kidney persisting for at least three months.

Decreased circulating complement C3 concentration · Frequent (79-30%)

Concentration of the complement component C3 in the blood circulation below the lower limit of normal.

Elevated circulating creatinine concentration · Frequent (79-30%)

An increased amount of creatinine in the blood.

Hypertension · Frequent (79-30%)

The presence of chronic increased pressure in the systemic arterial system.

Membranoproliferative glomerulonephritis · Frequent (79-30%)

A type of glomerulonephritis characterized by diffuse mesangial cell proliferation and the thickening of capillary walls due to subendothelial extension of the mesangium. The term membranoproliferative glomerulonephritis is often employed to denote a general pattern of glomerular injury seen in a variety of disease processes that share a common pathogenetic mechanism, rather than to describe a single disease entity

Mesangial hypercellularity · Frequent (79-30%)

Increased numbers of mesangial cells per glomerulus, defined as more than 3 nuclei fully surrounded by matrix in one or more mesangial areas, not including perihilar region, on a standard 3-micron-thick tissue section, best evaluated on periodic acid-Schiff (PAS) stain.

Other findings in the same source

From: Orphanet

Additional reported features include Nephrotic range proteinuria (Frequent (79-30%)); Proteinuria (Frequent (79-30%)); Stage 5 chronic kidney disease (Frequent (79-30%)); Abnormal dark-adapted electroretinogram (Occasional (29-5%)); Acute kidney injury (Occasional (29-5%)); Anti-Complement factor H antibody positivity (Occasional (29-5%)); Autoimmunity (Occasional (29-5%)); Crescentic glomerulonephritis (Occasional (29-5%)); Decreased circulating complement C4 concentration (Occasional (29-5%)); Drusen (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing C3 glomerulopathy is Nephrology, with a nephrologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• How is kidney function being assessed over time?
• Are any current medicines or supplements relevant to kidney safety?
• Is there an individual recommendation about fluids, diet or blood pressure?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for C3 glomerulopathy. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.