Tri­somy 21

Down syn­drome or Tri­somy 21 is a ge­netic dis­or­der caused by the pres­ence of all or part of a third copy of chro­mo­some 21.

The Star Malaysia - Star2 - - LIVING - DR y.L.m.

M Y new neigh­bours moved in re­cently, and I no­ticed their daugh­ter has Down’s Syn­drome. What is Down’s Syn­drome? Ac­tu­ally, it is called Down Syn­drome and not Down’s Syn­drome.

Down Syn­drome is a ge­netic dis­or­der. It is as­so­ci­ated with de­vel­op­men­tal de­lays, men­tal re­tar­da­tion and many other prob­lems.

It is the most com­mon ge­netic cause of learn­ing dis­abil­i­ties in chil­dren, and varies from per­son to per­son in sever­ity.

What do you mean by a ge­netic dis­or­der?

Ev­ery one of the cells in your body has a nu­cleus and cy­to­plasm. Ge­netic ma­te­rial – your DNA – is stored in the nu­cleus in chro­mo­somes, which are rod-like struc­tures that are grouped to­gether.

Each nu­cleus nor­mally con­tains 23 pair of chro­mo­somes. Half of th­ese are in­her­ited from your fa­ther, and the other half, from your mother.

In Down syn­drome, a per­son has a full or par­tial ex­tra copy of chro­mo­some 21. This is called Tri­somy 21 (tri = three). This is caused by ab­nor­mal di­vi­sion of ei­ther the sperm or egg cell.

How­ever, Tri­somy 21 is not the only way to get Down syn­drome. It is the rea­son for 90% of all cases, but there are two other ways, called mo­saic Down syn­drome and translo­ca­tion Down syn­drome. Is Down syn­drome very com­mon? I heard it is quite com­mon in chil­dren of women who get preg­nant af­ter 40 years of age. Down syn­drome is the most com­mon ge­netic con­di­tion in the world. In the United States, the in­ci­dence is ap­prox­i­mately one out of ev­ery 691 ba­bies.

It is true that as you age, hav­ing a child be­comes more risky for a host of things, in­clud­ing Down syn­drome, to oc­cur.

The risk fac­tors for hav­ing a child with Down syn­drome are:

> Hav­ing a child when you are older. This is be­cause older eggs carry a greater risk of im­proper chro­mo­some di­vi­sion. When you are 35 years old, your risk of hav­ing a child with Down syn­drome is one in 400. When you are 45 years old, the risk be­comes one in 35. It must be said that most Down syn­drome chil­dren are born to moth­ers be­low age 35 be­cause that group tends to have a lot more chil­dren than women over 45.

> If you have a child with Down syn­drome, you are more likely to have another child with Down syn­drome.

Was Down syn­drome dis­cov­ered by a man named Down?

Down syn­drome prob­a­bly ex­isted a long time ago, though it was prob­a­bly not as com­mon then be­cause women tended to have ba­bies very early, and they also tended to die early.

How­ever, it was a man called John Lang­don Down who ac­tu­ally pub­lished it in 1866. He was a Bri­tish physi­cian. He de­scribed it ac­cu­rately and as a sep­a­rate con­di­tion, and that is why the syn­drome bears his name.

How do I recog­nise some­one with Down syn­drome?

A baby who has Down syn­drome can be of av­er­age size at birth. But they tend to grow slowly and re­main shorter than other chil­dren of sim­i­lar age. They also hit de­vel­op­men­tal mile­stones later too, and start to crawl and sit up later.

A child with Down syn­drome has a dis­tinct fa­cial ap­pear­ance. It used to be de­scribed as “Mon­goloid”, but that term has now been dis­carded be­cause of it’s deroga­tory con­no­ta­tions. Th­ese fea­tures in­clude: > Flat­tened fa­cial fea­tures > Small head > Pro­trud­ing tongue > Short neck > Up­ward slant­ing eyes > Un­usu­ally shaped ears > Poor mus­cle tone > Broad, short hands with only one crease on the palm, un­like a nor­mal palm which has a lot of creases > Short fin­gers > Un­usual flex­i­bil­ity

Do peo­ple with Down syn­drome tend to die early?

They used to, but mod­ern medicine has made great ad­vances. A cen­tury ago, a baby born with Down syn­drome couldn’t live past age 10. Now, one can ex­pect to live past 50.

Of course, this de­pends on how many health prob­lems the per­son has. Chil­dren with Down syn­drome have com­pli­ca­tions that can be­come worse when they get older, in­clud­ing:

> Heart de­fects: hap­pens in half the chil­dren. If not treated, this can lead to an early death. > Leukaemia > In­fec­tious dis­eases (th­ese are more likely to de­velop than in nor­mal chil­dren) > Sleep ap­noea > Obe­sity > De­men­tia

Dr YLM grad­u­ated as a med­i­cal doc­tor and has been writ­ing for many years on var­i­ous sub­jects such as medicine, health, com­put­ers and en­ter­tain­ment. For fur­ther in­for­ma­tion, e-mail starhealth@ thes­tar.com.my. The in­for­ma­tion con­tained in this col­umn is for gen­eral ed­u­ca­tional pur­poses only. Nei­ther The Star nor the au­thor gives any war­ranty on ac­cu­racy, com­plete­ness, func­tion­al­ity, use­ful­ness or other as­sur­ances as to such in­for­ma­tion. The Star and the au­thor dis­claim all re­spon­si­bil­ity for any losses, dam­age to prop­erty or per­sonal in­jury suf­fered di­rectly or in­di­rectly from re­liance on such in­for­ma­tion.

Pri­mary cause: down Syn­drome is the most com­mon ge­netic cause of learn­ing dis­abil­i­ties in chil­dren. It varies from per­son to per­son in sever­ity. — reuters

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