What is Down Syndrome (Down's Syndrome) and What is Down Syndrome Screening?

What is Down Syndrome?

Down syndrome (mongolism, Down's syndrome, or trisomy 21), which is associated with typical facial features and reduced mental ability, is due to an extra chromosome 21 (genes - chromosomes). This syndrome is more common with increasing maternal age.

It is named after John Langdon Down, the British doctor who described the syndrome in 1866. The disorder was identified as a chromosome 21 trisomy in 1959. The condition is characterized by a combination of major and minor differences in structure. Often Down syndrome is associated with some impairment of mental ability and physical growth as well as facial appearance. A few have severe mental disability.

Many of the common physical features of Down syndrome also appear in people with a standard set of chromosomes. They may include:-

a single transverse palmar crease (a single instead of a double crease across one or both palms),
an almond shape to the eyes caused by an epicanthic fold of the eyelid, upslanting palpebral fissures (the separation between the upper and lower eyelids),
shorter limbs,
poor muscle tone,
a larger than normal space between the big and second toes,
and protruding tongue.

Health concerns for individuals with Down syndrome include

a higher risk for congenital heart defects,
gastroesophageal reflux disease,
recurrent ear infections,
obstructive sleep apnea, and
thyroid dysfunctions.

Is screening for abnormality in the fetus justifiable?

The question of screening for foetal abnormality is never an easy one.

Some would find the thought of caring for a handicapped child intolerable whereas others believe the practice of pregnancy termination is unacceptable (Q19.15).

When screening indicates that the fetus has a serious defect, there are two options.

Many couples elect to continue the pregnancy and the obstetrician in collaboration with the paediatrician can counsel on what is to be expected and the treatment options for the baby.
Other couples decide that they do not wish the pregnancy to continue and termination can be arranged. Counselling may be offered to provide support for you to come to terms with a decision to discontinue a planned pregnancy.

You will also need advice on the chance of recurrence in another pregnancy.

Your gynaecologist may be able to supply you with this information or otherwise arrange for you to see a clinical geneticist.

Picture of a mother and her baby with Down Syndrome

Healthcare systems appear to facilitate informed choices in the context of prenatal screening for Down syndrome screening less well for women from minority ethnic groups and those who are socioeconomically disadvantaged than for other women.^0501,While most pregnant women in England are offered prenatal screening for Down syndrome, approximately 1 in 10 is not. Asian women are less likely than White women to report being offered Down syndrome screening and are less likely to have a screening test when offered.⁰⁸⁰¹

What is the cause of Down Syndrome?

Down syndrome (mongolism), which is associated with typical facial features and reduced mental ability, is due to an extra chromosome 21 (genes - chromosomes).

This syndrome is more common with increasing maternal age.

A definitive diagnosis can only be reached from genetic (laboratory gene) evaluation of foetal cells obtained either from the amniotic fluid (the fluid around the baby during pregnancy) or from placental type cells (chorionic villus sampling).

We used to offer all mothers aged 37 years or more the option of amniocentesis; at the age of 37, the chance of having a Down’s baby is about 1 in 250 pregnancies.

Amniotic fluid is obtained (amniocentesis) by introducing a fine needle through the abdominal wall and uterus, usually with local anaesthetic, under ultrasound control.

There is an approximately 1% risk that this may cause miscarriage. The fetal cells are cultured in preparation for analysis of the chromosomes (genes). The culture may take two weeks or more.

Recently molecular biological techniques such as “FISH" (fluorescence in situ hybridisation) have been introduced. These techniques involve a more direct analysis of genetic material and provisional results can be provided within hours rather than weeks.

As the majority of babies are born to women younger than 37, most babies with Down syndrome were missed by the age-related screening programme.

Blood tests, including the triple or quadruple tests, could modify the risk for each pregnancy. Some women aged 37 years or more may find that the test shows that their risk is relatively low so that they would be happy to decline amniocentesis whereas for some younger women the test may show that their risk is greater than would have been indicated from their age and they may elect to have further investigation.

Ultrasound undertaken at around eleven weeks into the pregnancy with particular reference to the back of the baby’s neck (nuchal translucency) may provide a valuable guide to the risk of Down syndrome. It has been shown that ultrasound is more accurate than the blood test screening and it also has the advantage of screening five weeks before the quadruple test leading to earlier diagnosis or, hopefully, reassurance.

Interest is now focusing on a combination of ultrasound and early blood test screening. Nuchal translucency scans are performed from 11 to 13 weeks + 6 days of pregnancy. Before 11 weeks the scan is technically difficult because the baby is too small and, after 14 weeks, the excess fluid may be absorbed by the baby's developing lymphatic system. The skin appears as a white line, and the fluid under the skin is black.

Nuchal Translucency

Picture showing normal nuchal translucency.

Nuchal Translucency

Picture showing increased nuchal translucency - this baby is at increased risk for Down syndrome.

A nuchal translucency measurement of up to 2.0mm is normal at 11 weeks, and up to about 2.8mm by 13 weeks and 6 days. If the nuchal translucency is increased, it does not mean there is always a problem.

The spina bifida group of defects, and heart and limb defects may be demonstrated by ultrasound. Some families are prone to inherited disorders and many of these can be detected by specific screening techniques.

Screening tests are discussed in screening tests

Boy with Down Syndrome

Picture of a boy with Down syndrome.

Girl with Down Syndrome

Picture of a young woman with Down syndrome.

Support Groups

Members of a support group, provide each other with various types of help and information for a particular shared difficulty. The support may take the form of providing relevant information, relating personal experiences, listening to others' experiences, providing sympathetic understanding and establishing social networks. A support group may also provide ancillary support, such as serving as a voice for the public or engaging in advocacy. Support groups maintain interpersonal contact among their members in a variety of ways. Support groups also maintain contact through printed information rich newsletters, telephone chains, internet forums, and mailing lists.

Support groups offer companionship and information for people coping with diseases or disabilities. Support groups may not be appropriate for everyone, and some find that a support group actually adds to their stress rather than relieving it.t.

Evaluation of the quality of Web sites is discussed in(Q4.27) . You may find that several general women's health sites may help you (internet information). The following are more specialised relevant Web sites:-

www.downs-syndrome.org.uk/ Down's Syndrome Association
Langdon Down Centre
2a Langdon Park
Teddington
TW11 9PS http://www. Imdsa.com/ PO Box 1052, Franklin, TX 77856

Related Medical Abstracts - Click on the paper title:-

What is Down Syndrome and What is Down Syndrome Screening?