Ge­netic Dis­or­ders in Man

THISDAY - - FAMILY HEALTH - Chro­mo­somes: Genes Causes Sin­gle Gene Dis­or­ders Mul­ti­ple Genes Dis­or­der: Downs Syn­drome Au­to­so­mal re­ces­sive08053372356 (sms) only Causes of Down’s syn­drome Tests For Downs Syn­drome: Sickle Cell Anaemia: Symp­toms of sickle cell dis­ease : Causes Of Sickle C

The hu­man DNA is made up of 46 chro­mo­somes, and each man has a def­i­nite se­quence , and no two hu­man be­ings have the same gene makeup. This means that your ge­netic makeup is spe­cific to you and this gives you your hu­man ca­pa­bil­i­ties, shape, in­tel­li­gence, weak­nesses and strengths, sus­cep­ti­bil­ity to ill­nesses, and im­mu­nity , amongst other things. In the same way, any de­fect in your gene se­quence, re­sults in ge­netic dis­or­ders or ill­nesses. This would re­sult in var­i­ous man­i­fes­ta­tions of the ab­nor­mal gene for­ma­tion in your DNA. We all be­gan life as a sin­gle cell at con­cep­tion when an egg from your mum and sperm from your dad came to­gether. This sin­gle cell di­vided into two and then into four and so on un­til you de­vel­oped into a com­plete hu­man be­ing made up of bil­lions of cells. It was your genes that in­structed your cells to di­vide in this way and that con­trolled how you de­vel­oped. The role your genes play in shap­ing who you are doesn’t end at birth. Your genes are con­stantly be­ing used by your body through­out your life to keep it func­tion­ing. They in­ter­act with the en­vi­ron­ment around you and in­flu­ence ev­ery­thing from your health to your ap­pear­ance, your be­hav­iour and your per­son­al­ity. In­side al­most ev­ery one of oure cells is a tiny struc­ture called the nu­cleus which acts like the control cen­tre of the cell. In­side the nu­cleus are 46 chro­mo­somes. Each one is made up of a long strand of DNA. Along the length of the DNAs­trand are hun­dreds of genes (like beads on a piece of string – the string is the chro­mo­some and the beads are the genes). It is es­ti­mated that if a strand of DNAwas stretched out, it would be around two me­ters long, even though the av­er­age cell is smaller than a pin­head.

Our 46 chro­mo­somes come in 23 pairs. The chro­mo­some pairs are num­bered from the long­est, num­ber 1, to the short­est, num­ber 22. The 23rd pair of chro­mo­somes are our sex chro­mo­somes, the X and Y chro­mo­somes. Women have two X chro­mo­somes (XX) and men have one X and oneY chro­mo­some (XY). All the other chro­mo­somes are the same in males and fe­males. We in­herit one chro­mo­some in each pair from our mum and the other from our dad. : The strand of DNA which makes up each of your chro­mo­somes is ar­ranged into sec­tions called genes. Each gene is a sin­gle in­struc­tion which tells the body how to do a par­tic­u­lar job A ge­netic dis­or­der is a ge­netic prob­lem caused by one or more ab­nor­mal­i­ties in the genome, es­pe­cially a con­di­tion that is present from birth (con­gen­i­tal). Most ge­netic dis­or­ders are quite rare and af­fect one per­son in ev­ery sev­eral thou­sands or mil­lions. Ge­netic dis­or­ders may be hered­i­tary, passed down from the par­ents’ genes. In other ge­netic dis­or­ders, de­fects may be caused by new mu­ta­tions or changes to the DNA. In such cases, the de­fect will only be passed down if it oc­curs in the germ line. The same dis­ease, such as some forms of cancer, may be caused by an in­her­ited ge­netic con­di­tion in some peo­ple, by new mu­ta­tions in other peo­ple, and mainly by en­vi­ron­men­tal causes in other peo­ple. Whether, when and to what ex­tent a per­son with the ge­netic de­fect or ab­nor­mal­ity will ac­tu­ally suf­fer from the dis­ease is al­most al­ways af­fected by the en­vi­ron­men­tal fac­tors and events in the per­son’s de­vel­op­ment. Some types of re­ces­sive gene dis­or­ders con­fer an ad­van­tage in cer­tain en­vi­ron­ments when only one copy of the gene is present.

Ge­netic dis­or­ders can ei­ther be in­her­ited from both par­ents or from a sin­gle par­ent. Ge­netic dis­or­ders can be caused by a mu­ta­tion in one gene (mono­genic dis­or­der), by mu­ta­tions in mul­ti­ple genes (mul­ti­fac­to­rial in­her­i­tance dis­or­der), by a com­bi­na­tion of gene mu­ta­tions and en­vi­ron­men­tal fac­tors, or by dam­age to chro­mo­somes. Mono­genetic dis­or­ders are caused by a mu­ta­tion in a sin­gle gene. The mu­ta­tion may be present on one or both chro­mo­somes (one chro­mo­some in­her­ited from each par­ent). Ex­am­ples of mono­genic dis­or­ders are: sickle cell dis­ease, cys­tic fi­bro­sis, poly­cys­tic kid­ney dis­ease, and Tay-Sachs dis­ease. Ge­netic dis­or­ders can present as ei­ther Sin­gle gene or Mul­ti­ple gene dis­or­der.

A sin­gle-gene dis­or­der is the re­sult of a sin­gle mu­tated gene. Over 4000 hu­man dis­eases are caused by sin­gle-gene de­fects.[4] Sin­gle-gene dis­or­ders can be passed on to sub­se­quent gen­er­a­tions in sev­eral ways. Au­to­so­mal dom­i­nan­tOnly one mu­tated copy of the gene will be nec­es­sary for a per­son to be af­fected by an au­to­so­mal dom­i­nant dis­or­der. Each af­fected per­son usu­ally has one af­fected par­ent. The chance a child will in­herit the mu­tated

Two copies of the gene must be mu­tated for a per­son to be af­fected by an au­to­so­mal re­ces­sive dis­or­der. An af­fected per­son usu­ally has un­af­fected par­ents who each carry a sin­gle copy of the mu­tated gene (and are re­ferred to as car­ri­ers). Two un­af­fected peo­ple who each carry one copy of the mu­tated gene have a 25% risk with each preg­nancy of hav­ing a child af­fected by the dis­or­der. Ex­am­ples of this type of dis­or­der are Al­binism, sickle cell dis­ease. X-linked dom­i­nant Main ar­ti­cle: X-linked dom­i­nant X-linked dom­i­nant dis­or­ders are caused by mu­ta­tions in genes on the X chro­mo­some. Only a few dis­or­ders have this in­her­i­tance pat­tern, with a prime ex­am­ple be­ing X-linked rick­ets. Males and fe­males are both af­fected in these dis­or­ders, with males typ­i­cally be­ing more se­verely af­fected than fe­males. Some Xlinked dom­i­nant con­di­tions, are usu­ally fa­tal in males ei­ther in utero or shortly af­ter birth, and are there­fore pre­dom­i­nantly seen in fe­males

X-linked re­ces­sive-

X-linked re­ces­sive con­di­tions are also caused by mu­ta­tions in genes on the X chro­mo­some. Males are more fre­quently af­fected than fe­males, and the chance of pass­ing on the dis­or­der dif­fers be­tween men and women. The sons of a man with an X-linked re­ces­sive dis­or­der will not be af­fected, and his daugh­ters will carry one copy of the mu­tated gene. A woman who is a car­rier of an X-linked re­ces­sive dis­or­der (XRXr) has a 50% chance of hav­ing sons who are af­fected and a 50% chance of hav­ing daugh­ters who carry one copy of the mu­tated gene and are there­fore car­ri­ers.


Y-linked dis­or­ders are caused by mu­ta­tions on the Y chro­mo­some. These con­di­tions may only be trans­mit­ted from the het­eroga­metic sex (e.g. male hu­mans) to off­spring of the same sex. More sim­ply, this means that Y-linked dis­or­ders in hu­mans can only be passed from men to their sons; fe­males can never be af­fected.

Y-linked dis­or­ders are ex­ceed­ingly rare but the most well-known ex­am­ples typ­i­cally cause in­fer­til­ity. Re­pro­duc­tion in such con­di­tions is only pos­si­ble through the cir­cum­ven­tion of in­fer­til­ity by med­i­cal in­ter­ven­tion.


gene is 50%. Au­to­so­mal dom­i­nant con­di­tions some­times have re­duced pen­e­trance, which means al­though only one mu­tated copy is needed, not all in­di­vid­u­als who in­herit that mu­ta­tion go on to de­velop the dis­ease.

This type of in­her­i­tance, also known as ma­ter­nal in­her­i­tance, ap­plies to genes en­coded by mi­to­chon­drial DNA. Be­cause only egg cells con­trib­ute mi­to­chon­dria to the de­vel­op­ing em­bryo, only moth­ers can pass on mi­to­chon­drial DNA con­di­tions to their chil­dren.

Ge­netic dis­or­ders may also be com­plex, mul­ti­fac­to­rial, or poly­genic, mean­ing they are likely as­so­ci­ated with the ef­fects of mul­ti­ple genes in com­bi­na­tion with life­styles and en­vi­ron­men­tal fac­tors. Mul­ti­fac­to­rial dis­or­ders in­clude heart dis­ease and di­a­betes. Al­though com­plex dis­or­ders of­ten clus­ter in fam­i­lies, they do not have a clear-cut pat­tern of in­her­i­tance. This makes it dif­fi­cult to de­ter­mine a per­son’s risk of in­her­it­ing or pass­ing on these dis­or­ders. Com­plex dis­or­ders are also dif­fi­cult to study and treat, be­cause the spe­cific fac­tors that cause most of these dis­or­ders have not yet been iden­ti­fied.

There is also a strong en­vi­ron­men­tal com­po­nent to many of them ,

scle­ro­sis, can­cers dis­ease The most com­mon ge­netic dis­or­der in our own en­vi­ron­ment are sickle cell ane­mia, and Downs syn­drome.

Down’s syn­drome, also known as Down syn­drome or tri­somy 21, is a ge­netic con­di­tion that typ­i­cally causes some level of learn­ing dis­abil­ity and cer­tain phys­i­cal char­ac­ter­is­tics. Char­ac­ter­is­tics of Down’s syn­drome: lifeis­sues­[email protected]­

Most ba­bies born with Down’s syn­drome are di­ag­nosed soon af­ter birth and may have: Al­though chil­dren with Down’s syn­drome share some com­mon phys­i­cal char­ac­ter­is­tics, they don’t all look the same. A child with Down’s will look more like their fam­ily mem­bers than other chil­dren who have the syn­drome. Peo­ple with Down’s syn­drome will also have dif­fer­ent per­son­al­i­ties and abil­i­ties. Ev­ery­one born with Down’s syn­drome will have some de­gree of learn­ing dis­abil­ity, but this will be dif­fer­ent for each per­son.

Down’s syn­drome is usu­ally caused by an ex­tra chro­mo­some in a baby’s cells. In most cases, this isn’t in­her­ited – it’s sim­ply the re­sult of a one-off ge­netic change in the sperm or egg. There’s a small chance of hav­ing a child with Down’s syn­drome with any preg­nancy, but the like­li­hood in­creases with the age of the mother. For ex­am­ple, a woman who is 20 has about a 1 in 1,500 chance of hav­ing a baby with Down’s, while a woman who is 40 has a 1 in 100 chance. There’s no ev­i­dence that any­thing done be­fore or dur­ing preg­nancy in­creases or de­creases the chance of hav­ing a child with Down’s syn­drome.

of the pla­centa is tested, usu­ally dur­ing weeks 11-14 of preg­nancy

tested, usu­ally dur­ing weeks 15-20 of preg­nancy. If these tests show that your baby has Down’s syn­drome, you and your baby’s other par­ent will be of­fered coun­selling so you can talk about the im­pact of the di­ag­no­sis.

Sickle cell dis­ease is the name for a group of in­her­ited con­di­tions that af­fect the red blood cells. The most se­ri­ous type is called sickle cell anaemia.

Sickle cell dis­ease mainly af­fects peo­ple of African, Caribbean, Mid­dle East­ern, East­ern Mediter­ranean and Asian ori­gin. Peo­ple with sickle cell dis­ease pro­duce un­usu­ally shaped red blood cells that can cause problems be­cause they don’t live as long as healthy blood cells and they can be­come stuck in blood ves­sels. Sickle cell dis­ease is a se­ri­ous and life­long con­di­tion, al­though long-term treat­ment can help man­age many of the problems as­so­ci­ated with it.

Peo­ple born with sickle cell dis­ease some­times ex­pe­ri­ence problems from early child­hood, al­though most chil­dren have few symp­toms and lead nor­mal lives most of the time.

can be very se­vere and can last up to a week enough oxy­gen around the body), which can cause tired­ness and short­ness of breath

Some peo­ple also ex­pe­ri­ence other problems such as de­layed growth, strokes and lung problems.

Sickle cell dis­ease is caused by a faulty gene that af­fects how red blood cells de­velop.

If both par­ents have this faulty gene, there’s a 25% chance of each child they have be­ing born with sickle cell dis­ease. The child’s par­ents of­ten won’t have the con­di­tion them­selves be­cause they’re only car­ri­ers of the sickle cell trait.

Sickle cell dis­ease is of­ten de­tected dur­ing preg­nancy or soon af­ter birth. Screen­ing for sickle cell dis­ease in preg­nancy is of­fered to all preg­nant women , to check if there’s a risk of a child be­ing born with the con­di­tion, and all ba­bies are of­fered screen­ing as part of the new­born blood spot test (heel prick test).

Blood tests can also be car­ried out at any age to check for the con­di­tion or to see if you’re a car­rier of the faulty gene that causes it.

Due to the wide range of ge­netic dis­or­ders that are presently known, di­ag­no­sis of a ge­netic dis­or­der is widely var­ied and de­pen­dent of the dis­or­der. Most ge­netic dis­or­ders are di­ag­nosed at birth or dur­ing early child­hood how­ever some, such as Hunt­ing­ton’s dis­ease, can es­cape de­tec­tion un­til the pa­tient is well into adult­hood.

Ge­netic Dis­or­ders

Newspapers in English

Newspapers from Nigeria

© PressReader. All rights reserved.