néphropathie à IgA

The main job of the kidneys is to clear waste materials from the body and maintain a normal balance of fluids and chemicals in the body. The kidneys also have other functions such as helping to control blood pressure.

What is the cause of IgA nephropathy?

Diagramme en coupe du tractus urinaire

IgA nephropathy is one of a group of conditions called glomérulonéphrite. In the outer part of the kidneys, tiny blood vessels cluster together to form structures called glomeruli. These filter the blood to make urine.

IgA nephropathy is caused by antibodies called IgA being trapped in the kidney and causing damage to the kidney. IgA is short for 'immunoglobulin A'. IgA is a type of antibody our body produces to fight infection. Antibodies are small proteins that circulate in the bloodstream. They are part of the body's defence (immune) system and are sometimes called immunoglobulins. They are made by B lymphocytes - a type of white blood cell.

The IgA gets to the kidneys in the bloodstream and then causes scarring and inflammation in the kidney. The scarring and inflammation are very small and can only be seen with a microscope. The glomeruli are damaged by deposits of IgA. IgA nephropathy does not usually run in families, so you need not worry about passing it on to your children.

The cause of IgA nephropathy is not completely understood. IgA is produced by glands around the throat and bowel to fight off infection. IgA is normally two antibody molecules stuck together.

In IgA nephropathy, these molecules appear to get joined up in longer chains. As these travel around in the blood and pass through the kidney they get stuck in the filters (glomeruli) in the kidney.

The trapped IgA then causes an inflammatory reaction. It is not known why these IgA chains develop.

IgA nephropathy is very uncommon. However, IgA nephropathy is the most common cause of glomérulonéphrite. IgA nephropathy most often starts between 16 and 35 years of age.

The symptoms caused by IgA nephropathy are very variable from person to person. Many people with IgA nephropathy do not have any symptoms. IgA nephropathy is usually painless but sometimes an acute attack can cause pain over the kidneys and a feeling of sickness (nausea) for a couple of days.

However, the damage to the filters (glomeruli) of the kidneys may cause some blood to appear in the urine. Usually there is only a very small amount of blood in the urine. Therefore any traces of blood in the urine are often invisible and only detected on routine medical check-ups. In other cases there may be a lot more blood which you can see and comes in attacks every so often.

There may also be protein leakage from the kidneys. This may be slight and only detectable on urine tests. Occasionally, high levels of protein leakage cause swollen ankles, with very low levels of protein and high levels of cholesterol in your blood. This is called le syndrome néphrotique.

Sometimes a une maladie semblable à la grippe causes an increase in IgA getting to the kidney. This can cause an increased amount of blood in the urine, which then clears after a few days.

IgA may cause the blood pressure to increase (hypertension). This damages the kidneys and may also put a strain on the heart. It is therefore very important to treat high blood pressure if it develops. Maladie rénale chronique may sometimes occur. Very occasionally and much less often, IgA nephropathy may cause lésion rénale aiguë before any other symptoms have developed.

The first tests include urine tests to check for a urine infection and to measure the protein in your urine. Collecting all of your urine over 24 hours may be needed to see how much protein is leaking from your kidneys. Blood tests will include tests to see how well your kidney is working.

The scarring and inflammation in the kidney can only be seen with a microscope. Therefore, IgA nephropathy is normally only diagnosed after a sample (biopsy test of the kidney) is taken.

There is no specific treatment to cure IgA nephropathy. However, there are many treatments that can help to protect the kidneys and so improve the outlook:

• It is very important to have regular blood pressure checks and to keep your blood pressure normal.

• It is also important to have regular urine checks to see if there is any protein or blood in the urine.

• Treatment needs to be started early if blood pressure levels become high. Treating high blood pressure levels helps to reduce any damage to the kidneys.

• Treatment with steroids is controversial but steroids may reduce the amount of protein leaking from the kidneys into the urine. Steroids may also reduce the risk of chronic kidney disease and kidney failure (end-stage kidney disease).

The medicines used for blood pressure control with IgA nephropathy are Inhibiteurs de l'enzyme de conversion de l'angiotensine (ECA) or angiotensin receptor blockers (ARBs) - for example, losartan. Even if you don't have high blood pressure, Both ACE inhibitors and ARBs can reduce your risk of developing la maladie rénale chronique. Sometimes ACE inhibitors and ARBs are used together.

Corticostéroïdes can also help to reduce the amount of protein in the urine and reduce your risk of chronic kidney disease.

Medicines called statines may be needed to treat high cholesterol. Your cholesterol may increase because of IgA nephropathy.

Other treatments that may help include other medicines to reduce your defence (immune) system (for example, azathioprine). Medicines that prevent blood clotting in your blood vessels (anticoagulants) have also been used. Removing your tonsils (tonsillectomy) may be used to reduce the amount of IgA in your bloodstream and so reduce any further damage to your kidneys.

If you develop la maladie rénale chronique, this may become severe (end-stage kidney disease). You will then probably need treatment with dialysis and a kidney transplant. Most people with IgA nephropathy do not develop chronic kidney disease. There is a risk of the transplanted kidney becoming affected by IgA nephropathy.

The outlook (prognosis) is very variable from person to person.

• IgA nephropathy may get better on its own without any further problems.

• IgA nephropathy may continue unchanged for many years. You will then only need regular check-ups with urine and blood tests.

• About 1 in 3 people with IgA nephropathy develop la maladie rénale chronique.