Down Syndrome: • Learning about the condition
Monday, March 21, 2016 marked the 11th anniversary of World Down Syndrome Day. Each year, the voice of people with Down Syndrome, and those who live and work with them, grows louder.
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The day aims to conduct activities and events to help raise awareness of what Down Syndrome is, what it means to have Down Syndrome and how people with Down Syndrome play a vital role in our lives and communities.
About Down Syndrome
Down Syndrome (DS), also called Trisomy 21, is a condition in which a child inherits extra genetic material from the parent causing delays in the way the child develops, both mentally and physically. The disease is named after a British physician, John Langdon Down who first described it in 1887. It affects about one in every 800 babies.
The reason why Down Syndrome occurs is exactly not known, but we know that it results from an error in chromosomal arrangement. It is also known that women aged 35 and older have a significantly higher risk of having a child with the condition.
Normally, at the time of conception, a baby inherits genetic information from its parents in the form of 46 chromosomes, 23 from the mother and 23 from the father. In most cases of Down Syndrome, a child gets an extra copy of the genetic material either in whole or in part located on the chromosome 21 — making a total of 47 chromosomes instead of 46. It is this extra genetic material that causes the physical features and developmental delays associated with Down Syndrome. It is also important to note that the effects and extent of the extra copy vary greatly among people, depending on genetic history and pure chance.
By the time a female child is born, her eggs are in a certain stage of cell division where the chromosome materials called chromatids are in a mesh making direct contact with each other. They continue to remain in contact with each other until ovulation where that particular egg quickly completes the cell division leading to a mature egg and an immature one called a polar body. Because these chromatids are in contact with each other, they tend to form strong bonds with each other such that separating them becomes difficult during cell division. Thus the more advanced in years the woman is during ovulation, the longer the period that the chromatids have been in contact with each other, and the more difficult the separation leading to an extra copy of the chromosome being pulled by the other. This process is called non-disjunction and is mostly seen in women older than 35 years of age.
Influence of extra copy chromosome
Non-disjunction, a gamete (i.e., a sperm or egg cell) is produced with an extra copy of chromosome 21; the gamete thus have 24 chromosomes instead of 23. When combined with a normal gamete from the other parent, the embryo now has 47 chromosomes, with three copies of chromosome 21. In this all the cells in the body have extra copy of chromosome 21.
Sometimes some of the cells in the body are normal and other cells have trisomy 21, this is called Mosiacism. Another way of getting extra genetic materials on chromosome 21 is a form called translocation. In this case, the long arm of chromosome 21 is attached to another chromosome, often chromosome 14. A person with such a translocation is normal in appearance. Translocation Down Syndrome is often referred to as familial Down Syndrome. It does not show the maternal age effect that can be seen in younger mothers and is just as likely to have come from fathers as mothers.
Rarely, a region on chromosome 21 will undergo a duplication event leading to extra copies of some, but not all, of the genes on chromosome 21. If the duplicated region has genes that are responsible for Down Syndrome; physical and mental characteristics, such individuals will show those characteristics.
Physical characteristics
The physical features and medical problems associated with Down Syndrome can vary widely among individuals, with some children with the condition leading a normal life while others need a lot of medical attention.
Children with Down Syndrome tend to share certain physical features such as a flat facial profile, an upward slant to the eyes, widened space between the eyes, small ears, and a protruding tongue. Other features are short stubby fingers, single crease in the palms and a wide gap between the first and second toes. At birth, children with DS are usually of average size, but they tend to grow at a slower rate and remain smaller than their peers. For infants, low muscle tone may contribute to sucking and feeding problems as well as floppy appearance. They also have constipation and other digestive issues. Toddlers and older children may have delays in speech and self-care skills such as feeding, dressing and toilet training. One of the constant features of DS is delayed developments.
Down Syndrome affects the child’s ability to learn in different ways, but most have mild to moderate intellectual impairment. However, children with DS can and do learn, and are capable of developing skills throughout their lives. They simply reach goals at a different pace — which is why it is important not to compare a child with DS against a normal sibling or even other children with the condition because they are always mentally retarded though to various degrees.
In addition, children with DS can have significant medical conditions. Almost half of all children born with DS will have a heart problem, mostly a hole in heart, hearing and visual impairment, lung problems such as Pulmonary hypertension, thyroid problems, intestinal abnormalities, seizure disorders, respiratory problems, obesity, an increased susceptibility to infection, and a higher risk of childhood leukemia.
Detecting Down Syndrome
Two types of prenatal tests are used to detect Down Syndrome in a fetus: screening tests and diagnostic tests. Screening tests estimate the risk that a fetus has DS; diagnostic tests can tell whether the fetus actually has the condition.
Screening tests are cost-effective and easy to perform. But because they don't give a definitive answer as to whether a baby has Down Syndrome, these tests are used to help parents decide whether to have more diagnostic tests. They include Nuchal translucency testing and Tripple or quadruple tests.
Diagnostic tests are about 99 per cent accurate in detecting Down Syndrome and other chromosomal abnormalities. However, because they're performed inside the uterus, they are associated with a risk of miscarriage and other complications. Examples include chorionic villus sampling and amniocentesis.
Though Down Syndrome can't be prevented, it can be detected before a child is born. The health problems that can go along can be treated and there are many resources available to help children and their families who are living with the condition. Children with DS are very affable, humorous and full of life. That not all is lost is attested to by Paula Sage, a patient with DS who is a celebrated British actress with a BAFTA award to her honour.
Writer’ e-mail : [email protected]
The writer is a member of Paediatric Society of Ghana.