The exact cause of primary biliary cirrhosis (PBC) is unknown, although it is thought that a combination of genetic and environmental factors may play a part. These factors are described below.
- Genetic factors – the genes that you inherit make you susceptible to developing PBC
- Environmental factors – something in the environment triggers PBC (see possible triggers, below)
Autoimmune condition
Most experts believe that PBC is an autoimmune condition. In these types of conditions, something goes wrong with the immune system (the body’s natural defence against infection and illness). Instead of fighting off infection, the immune system attacks healthy tissue.
In cases of PBC, the immune system sends specialised cells, known as T-cells, to the site of the bile ducts. T-cells usually kill bacteria and viruses.
The T-cells will start to damage the surface of the bile ducts, which will gradually become extensively scarred and disrupt the usual flow of bile. As the amount of bile in the liver increases, further scarring of the liver (cirrhosis) occurs.
Over time, high levels of cirrhosis will cause the liver to lose some, and eventually all, of its function. As the liver plays a vital role in filtering out impurities from your blood, a loss of liver function is potentially fatal.
It is not known what causes the immune system to malfunction and attack the bile ducts.
Other autoimmune conditions
Having one autoimmune condition such as PBC can make it more likely that you will have other autoimmune conditions. For example, people with PBC may also have:
- autoimmune thyroid disease – a condition that affects the thyroid gland in your neck, which produces hormones
- an underactive thyroid (hypothyroidism) – a type of thyroid condition where the thyroid gland does not produce enough hormones; around a fifth of people with PBC also have an underactive thyroid gland, which may be responsible for the fatigue
- rheumatoid arthritis – a condition that causes pain and swelling in the joints
- scleroderma – a condition that affects the connective tissue (the supporting tissues of the body), causing hard, puffy and itchy skin
- autoimmune hepatitis – a very rare cause of chronic (long-term) hepatitis, where the white blood cells attack the liver
- Sjogren's syndrome – a disorder where the white blood cells attack the body’s tear and saliva glands
- Raynaud's phenomenon – a common condition of the blood vessels that supply blood to the skin, causing them to narrow and reduce blood flow to the hands
- coeliac disease – a common digestive condition where a person is intolerant (has an adverse reaction) to the protein gluten
Risk factors
There is some evidence to suggest that certain risk factors can increase your chance of developing PBC. These risk factors are explained below.
Sex
Being female is the most significant risk factor for developing PBC. Less than 1 in 10 cases of PBC occur in men.
A number of theories have sought to explain why PBC is more common in women. One theory is that the immune system is different because of the female sex hormone, oestrogen. Another theory is that PBC may occur as a complication of pregnancy. However, there is currently no evidence to support or disprove these theories.
Family history
Having a close relative with PBC means that you are more likely to develop the condition yourself. For example, if you are female and your mother has or has had PBC, you are much more likely to develop PBC than someone who has no relatives with the condition. However, the risk is still low. More than 99% of people who have a first-degree relative with PBC will not develop the condition themselves.
This family connection has led researchers to speculate that certain genes (units of genetic material) inherited from your parents may make you more likely to develop PBC.
Possible triggers
There are some factors that may trigger PBC in people with a genetic tendency. Possible triggers could include:
- infections, such as a urinary tract infection
- hormone replacement therapy (HRT) – a treatment used to replace the female hormones that a woman’s body is no longer producing because of the menopause
- using nail varnish or cosmetics
- smoking cigarettes or having a past history of heavy smoking
- living near to where toxic waste has been dumped
However, none of the above triggers have been proven as definite triggers of PBC. Most people who are exposed to them will not develop the condition. At present, there is nothing to suggest that you should reduce your exposure to these triggers to lower your risk of developing PBC.
