Around 750 children are born with Down's syndrome in the UK each year. Women of high maternal age and mothers with previous Down's babies are particularly at risk. Some data suggests that three children per day are aborted because of an ante-natal diagnosis of the condition.
Ante-natally, the probability of having a Down's baby is determined by the combination of specialised imaging carried out at around 12 weeks of pregnancy, called the nuchal scan, and a series of blood tests.
The nuchal scan measures the thickness of skins folds at the back of the neck. A thick nuchal fold is associated with a higher risk of Down's syndrome.
If the probability of having an affected child is high, a couple may elect to have chromosomal testing, usually by amniocentesis or chorionic villus sampling. Not all couples will want to be tested or, indeed, to have a termination of pregnancy if Down's syndrome is confirmed.
By far the majority of cases are caused by an extra chromosome 21. This is why Down's is sometimes referred to as 'trisomy 21'. Other causes can be complex, and include chromosomal 'translocations' and genetic 'mosaicism'. A number of other trisomy conditions exist, including Edward's and Patau syndromes, caused by an extra chromosome 18 or 13 respectively.
Complications
Many children with Down's syndrome attend mainstream school. It is important to be aware of the health complications related to the condition. Sadly, around one in 20 children will die before reaching five years of age, and adults with Down's tend not to live beyond their fifties or sixties, sometimes due to infection, cardiac disease or leukaemia.
People with Down's may have a mild, moderate or severe learning disability, and they don't develop as quickly as other children. Specialised Down's growth charts should be used when monitoring development in these children. These charts may be downloaded for free on the internet.
On average, by the time an affected person is 21 years old, they have a mental age of around five years. The risk of Alzheimer's disease is much higher and it usually develops in the sixth decade of life.
In a person with Down's syndrome the ears are lower than normal - so-called low set ears - and the bridge of the nose is flat. Extra folds of skin, called epicanthic folds, give the eyes their characteristic appearance. Short-sightedness and long-sightedness are common, as are blocked tear ducts. The mouth is often held open and the tongue protruded. If you look at the hands and feet of someone with Down's syndrome, you may find they have a single crease along their palms and a wide gap between the great and second toes known as a sandal-gap toe. Glue ear is common, so you should not assume a Down's child's inattention is solely due to learning difficulties.
Heart abnormalities may affect up to 60 per cent of people with Down's. Common defects include a hole in the heart, such as a ventriculo-septal defect, or more complex cardiac conditions, including Fallot's tetralogy. In this condition, in addition to a hole in the heart, blood is prevented from flowing to the lungs easily, causing children to turn blue. Children with cardiac defects usually have surgery at a very young age. Heart conditions may cause the child to be breathless and may reduce their growth potential.
The gut may also not form properly. Duodenal atresia describes a condition where the part of the gut just beyond the stomach hasn't developed and won't allow the passage of stomach contents; urgent surgery is required. Hirchsprung's disease, which is more common in Down's syndrome, is caused by poor nerve supply to segments of the bowel. Feeding difficulties are very common, partly related to poor muscle control. Constipation, which is very common in Down's syndrome, isn't necessarily indicative of serious bowel disease.
While poor feeding can cause growth difficulties, people with Down's ultimately become overweight. Diet and exercise should be managed appropriately. An underactive thyroid is more common in Down's syndrome than the general population, and is one of the reasons why obesity is prevalent.
The management of Down's syndrome is complex and requires support for the family as well as the individual concerned. All agencies, including teachers, doctors and social services, may be required to ensure that those affected are given holistic and compassionate care.
- Dr Raj Thakkar BSc(Hons) MBBS MRCGP MRCP(UK) is a full-time GP in Buckinghamshire
