Sickle cell disease can cause a wide range of symptoms.
These can start from a few months of age, although many children have few or no symptoms if treatment is started early on.
The main symptoms are:
Episodes of pain known as sickle cell crises are one of the most common and distressing symptoms of sickle cell disease.
They happen when blood vessels to part of the body become blocked.
The pain can be severe and lasts for up to 7 days on average.
A sickle cell crisis often affects a particular part of the body, such as the:
How often someone with sickle cell disease gets episodes of pain varies a lot.
Some people may have one every few weeks, while others may have less than 1 a year. The average is 1 bad episode a year.
It's not always clear what triggers bad pain, but sometimes painful episodes can be caused by the weather (such as wind, rain or cold), dehydration, stress or strenuous exercise.
People with sickle cell disease are more vulnerable to infections, particularly when they're young.
Infections can range from mild, such as colds, to much more serious and potentially life threatening, such as meningitis.
Vaccinations and daily doses of antibiotics can help reduce the risk of many infections.
Nearly all people with sickle cell disease have anaemia, where the haemoglobin in the blood is low.
Haemoglobin is the substance found in red blood cells that's used to transport oxygen around the body.
This does not usually cause many symptoms, but sometimes it can get worse if you become infected with the virus that causes slapped cheek syndrome (parvovirus).
It's usually treated with a blood transfusion.
Sickle cell disease can also sometimes cause a wide range of other problems.