'Doctor, my baby has been diagnosed with sickle cell anaemia, and I don't understand what this means.'
Sickle cell anaemia, which is screened for in the UK, is a potentially devastating disease that needs a huge amount of education, vigilance and care from doctors, nurses, teachers and family. Its management is complex and beyond the scope of this article. Suffice to say, it is crucial that those looking after children with sickle cell disease understand its potential complications and the need to seek medical advice whenever problems arise.
Anaemia, of all types, is defined as a reduction in haemoglobin, the iron-protein structure that allows red blood cells to carry oxygen around the body. While the most common type is iron deficiency, often caused by poor diet or excess blood loss, sickle cell anaemia is different in that it has a genetic basis, inherited from abnormalities in parental genes.
If both people in a couple are sickle cell carriers (that is, they each have a normal haemoglobin gene and a sickle gene), several gene patterns may be generated in their offspring:
- There is a 25 per cent chance the child may inherit both normal genes, in which case the child is completely unaffected
- There is a 50 per cent chance the child will inherit one normal and one sickle cell gene and hence be a sickle carrier which is known as sickle cell trait
- There is, however, a 25 per cent chance the child may inherit the abnormal gene from each parent and thus have sickle cell disease.
The type of haemoglobin in the foetus and newborn baby is different from mature 'adult' haemoglobin, and it takes a few months after childbirth for this transformation to take place. Foetal haemoglobin is unaffected by sickle cell anaemia and consequently, despite inheriting both abnormal genes, the disease doesn't become manifest until the infant's haemoglobin matures.
Normal red blood cells are biconcave in shape which allows them to transfer as much oxygen as possible whilst being able to squeeze through the smallest of blood vessels. Red blood cells in people with sickle cell anaemia are more fragile than normal red blood cells. In addition, they may literally adopt a sickle-type shape when under stress from, for example, dehydration, low oxygen or infection. This sickling prevents cells from moving through small blood vessels easily, so increasing the risk of blockage, known as vaso-occlusion.
This prevents sufficient oxygen reaching tissues, with consequent cell damage or even cell death. In addition, the sickle-shaped cells break down more readily than healthy ones, resulting in anaemia that may cause tiredness and breathlessness. Breakdown products of the fragmented red blood cells may accumulate in the gallbladder forming gallstones.
COMPLICATIONS
Poor oxygen supply to bones can lead to severe pain resulting in what's known as a bony crisis. Swollen and painful digits due to vaso-occlusion causes a condition described medically as dactylitis. It occurs in both the hands and the feet most commonly in children between six months and three years of age.
Particular bony structures such as the top of the femur can lose their blood supply, leading to what is termed avascular necrosis. This may cause breakdown of the affected bone leading to pain and eventual arthritis.
People with sickle cell anaemia are also more susceptible to infection of the bone, known as osteomyelitis, particularly by bacteria such as salmonella or staphylococci.
Infection by parvovirus B19, the same virus that causes slapped cheek syndrome, can be fatal in people with sickle cell anaemia, rendering the bone marrow ineffective by causing an aplastic crisis. In this uncommon condition, the patient becomes severely anaemic, has little in the way of white cells, which fight infection, and low platelets which leads to bruising and excessive bleeding.
Sickle cell anaemia may affect the spleen in two main ways. Splenic sequestration most commonly occurs in the first five years of life, and manifests with rapid enlargement of the spleen and severe anaemia, and is considered a medical emergency.
Repeated vaso-occlusion of the spleen eventually damages it so much it is rendered useless. Given the spleen helps to protect against infections such as meningococcal meningitis and pneumococcal disease, it is important these people take daily preventative antibiotics and are up to date with vaccinations.
Other organs that may be affected include the kidney, liver, heart, lungs, brain, skin and eye. Vaso-occlusion of these organs may cause kidney failure, liver damage, heart attack, permanent lung disease, stroke, skin ulcers and blindness.
Dr Raj Thakkar BSc(Hons) MBBS MRCGP MRCP(UK) is a full-time GP in Buckinghamshire
