sábado, 17 de maio de 2008

Síndroma de Down - rastreio, escrito por Dr. Mário Pires

A Síndroma de Down é causada por uma alteração no cariótipo do bebé, o qual possui 47 cromossomas, devido a uma cópia extra do cromossoma 21. Em 95% dos casos esta mutação tem origem durante a formação dos gâmetas. Ocorre a não-disjunção do par (de cromossomas) 21, e obtém-se assim um gâmeta com 24 e outro com 22 cromossomas. 90% das vezes, o gâmeta envolvido é o oócito. Se este oócito anormal (com 24 cromossomas) for fecundado por um espermatozóide normal, o ovo resultante possuirá um total de 47 cromossomas e 3 cópias do 21, ou seja trissomia 21. 3 a 4% dos casos de Síndroma de Down ocorrem devido a uma mutação denominada translocação robertsoniana. Nestes casos durante a gametogénse há um rearranjo genético entre os cromossomas 14 (mais frequentemente) e 21, de forma a que o cromossoma 14 fique com material extra do 21. Assim, após a fecundação o número total de cromossomas é normal (46), mas temos material cromossómico 21 em triplicado.

Os restante casos de Trissoma 21 são originados por erros de divisão após a fecundação. Daqui resultam mosaicos, indivíduos que possuem uma mistura de linhagens celulares, umas com Trissomia 21, outras normais. Nestes casos, a percentagem relativa de células com Trissomia, determina a gravidade da Síndroma.

Factores risco


O único factor de risco bem documentado é a Idade materna avançada, À medida que a mulher envelhece, aumenta a probabilidade dos seu óvulos sofrerem alterações cromossómicas na divisão. A probabilidade de aos 35 anos ter um filho com Down é de 1/385, aos 40 de 1/160 e aos 45 de 1/30. No entanto a maioria das crianças com Síndroma de Down nasce de mulheres com menos de 35 anos, pois este é um grupo muito mais fértil.

No caso de existir um filho anterior com Síndroma de Down, existe uma probabilidade de 1% de voltar a ter um filho com esta condição.

Diagnóstico pré-natal


Actualmente é possível fazer o diagnóstico pré-natal desta condição. São usadas várias técnicas (rastreio bioquímico, rastreio ecográfico, amniocentese, biopsia das vilosidades coriónicas), no entanto apenas a amniocentese e biopsia das vilosidades nos fornecem um verdadeiro diagnóstico, as outras técnicas simplesmente dão probabilidades.


O rastreio ecográfico e bioquímico são geralmente feitos entre as 11 e as 14 semanas de gestação. Na ecografia, a nuca do feto é analisada (é medida a sua translucência aos ultrasons). Actualmente esta medida é combinada com os resultados do rastreio bioquímico, no qual são quantificadas várias substâncias (PAPP-A, β-HCG,... ) no sangue materno, e outros factores como idade, peso, raça, hábitos tabágicos maternos e idade gestacional. A análise matemática destes parâmetros fornece um valor de risco de o bebé sofrer de Trissomia 21.

Se os testes de rastreio forem considerados positivos, risco superior a 1/300 ou 1/400 (dependendo do método usado), pode-se recorrer à amniocentese ou à biopsia das vilosidades, para verificar se existe ou não Trissomia 21 (cerca de uma em 20 grávidas têm um teste de rastreio positivo, número bem superior ao de bebés com Trissomia 21)

Na amniocentese, é obtida uma amostra de liquido amniótico (o útero é puncionado com uma agulha, através da parece abdominal), que é usada para estudar o cariótipo fetal. Este exame implica um risco de aborto de 1/200. Na biópsia das vilosidades coriónicas, são obtidas células da placenta, que são igualmente usadas para estudar o cariótipo fetal. Mais uma vez, este procedimento implica risco de aborto (1/100). Estes exames invasivos têm uma exactidão entre 98 e 99%.

Quem deve fazer?

Tradicionalmente o diagnóstico pré-natal era efectuado consoante a a idade da mulher. A amniocentese era oferecida às mulheres com mais de 35 anos. Actualmente, com o fácil acesso aos métodos de rastreio analítico e ecográfico, a maioria das mulheres realizam um, ou ambos, destes testes de rastreio.

Dr. Mário Pires

15/05/2008

Síndroma de Down

video

Sindroma de Down - gémeos de 1 em 1 milhão

The twins who are 'one in a million'

By MORAG TURNER - More by this author » Last updated at 22:42pm on 20th July 2007


When 42-year-old Cathleen Gardiner's twins were born 17 years ago, doctors told her they were a "pair in a million".

One had Down's syndrome, while the other did not. Here, Cathleen, a former IT specialist who lives in Strathclyde with her husband Paul, an account manager for Yellow Pages, tells MORAG TURNER their touching and inspiring story...

Relaxing on the beach in Ibiza, I couldn't have been happier as I watched my twins, Sean and Lisa, then eight, playing in the sand with their five-year-old brother Daniel.

They spent hours pottering about with their buckets and spades together like best friends. Every so often I'd wander down to the water's edge to reapply their sun cream or give them a drink.

It was after one of these trips that the woman lying on the lounger beside mine turned and said to me: "I think it's so brave of you to bring your son on holiday with you. It's so nice he gets to be part of the family."

At first I didn't really know what she was talking about - of course I'd take all of my children on holiday!

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 Gardiner

Two peas in a pod: Lisa Gardiner has always shared a remarkable bond with her brother Sean

She must have spotted my bewildered look because she pointed to Sean and said: "I mean Down's syndrome is such a difficult thing to live with, it's amazing you manage to cope being so far from home.

"I know a family with that kind of child and they'd never be able to do this."

"I don't think she meant to be cruel or insensitive, but at the same time I wanted to scream: 'How dare you talk about my son as if he's someone to be left at home while the rest of us enjoy a fortnight in the sun.'

Since Sean was born 17 years ago, I have always taken the view that he is just as wonderful and special as my other two children.

While he may have a disability, none of us have ever viewed him as a burden, and despite meeting plenty of people over

the years with views as negative as that woman on the beach, I refuse to see him as anything but a blessing.

Cases of having one twin with Down's and one without are extremely rare. I've heard of only a handful of similar situations around the world.

Certainly when I found out I was expecting it was the last thing on my mind.

My husband Paul and I were both only 22 and had been married for just a year, but we couldn't wait to start a family and when I fell pregnant after only a month of trying we were over the moon.

When I was told I was having twins I was delighted, and I was carefully monitored throughout because of the increased risk of premature birth associated with a multiple births.

I had lots of scans - seven in total, which is far more than most women get.

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 Gardiner

Inseparable: Lisa and Sean as babies

During these, and after all my blood tests, I was told everything looked normal and that my two babies were healthy.

I was briefly told about Down's syndrome, but no one indicated it was a real possibility and it certainly wasn't suggested that I have an amniocentesis - the most effective diagnostic test for the condition, where a little fluid from around the baby is extracted by a needle and screened.

Even if they had offered it to me I would have said no because both Paul and I felt strongly that no matter what, we would never terminate a pregnancy.

However, I do not condemn women who decide to terminate their pregnancy when they discover their baby is disabled.

On June 18, 1990, at 37 weeks, I went into hospital to have a Caesarean. When I came round, Paul was by my bedside beaming from ear to ear.

"It's a boy and a girl! They're beautiful!" he exclaimed.

An hour later they wheeled me along to the nursery to see the twins and I was instantly struck by how adorable they were.

We named them Lisa and Sean and I could barely tell them apart. Not for a minute did I think my son looked anything other than normal.

Little did I realise that my world was about to be turned upside down by news no one had predicted.

The next day, a nurse appeared at the bottom of my bed asking Paul and me to come to a meeting with a paediatric doctor.

Closing the door behind him, the doctor immediately said to us: "We believe your son has Down's syndrome."

It was a like a bombshell hitting us. There was no history of the condition on either side of our family and I was only 22 - I'd always thought this was something that affected women in their 40s, not someone healthy and young like me.

Despite the shock, we were both remarkably calm and strong.

Maybe it's the fact that we are Catholics and strong believers that your hand in life is dealt to you by God for a reason, but I suddenly felt incredibly blessed.

Sean was special and in that moment, gazing at his tiny little face, I knew I had been chosen to be his mother because I felt I would be able to deal with what lay ahead.

As I looked at Sean lying in his cot, I didn't feel any less love for him than I did for his sister.

He was still my precious little baby and the fact that he had a disability didn't change that.

Once I knew he had Down's I could see slight differences in his appearance to that of Lisa - such as his tongue being much longer, a classic sign - but they didn't stop me thinking he was gorgeous.

What really puzzled me, of course, was that I'd had one "normal" twin and one with Down's.

The doctors explained that as they were fraternal twins, meaning they came from two eggs, rather than identical twins, where one egg is split in two, Lisa was not affected by the condition.

My biggest worry was what Sean's quality of life would be. I was also concerned about the impact it would have on Lisa's life and ours.

From the outset I wanted to make sure we had as normal a family as possible for everyone's sake.

But as soon as we got Sean home it was extremely apparent that he was very different to his sister.

As they were exactly the same age, it made his Down's even more obvious.

If you just have one child with the condition you don't have another one to constantly compare them to, and I'll admit it was very hard to watch Lisa rapidly grow and develop while Sean lagged so far behind.

She was bright and alert, while Sean was floppy and not nearly so aware of his surroundings.

Lisa walked at 11 months, while Sean didn't take his first steps till he was three.

By two, Lisa was quite the conversationalist, but Sean wasn't able to form sentences until he was nearly four.

For the first five years of his life, Sean needed a great deal of care.

There was no question of me going back to my job as a technical adviser in a computing company. Looking after him was a fulltime job.

He had to see a doctor, a physio and a speech therapist every week to help with his walking and talking. It took until he was school age for him to learn skills like feeding himself.

Yet despite the considerable difference between the twins, we never treated them differently. We gave them the same toys and spoke to them the same way.

Our attitude was that by encouraging Sean to keep up with Lisa, even though he would never manage it, we would be helping him to fulfil his potential.

It's a strategy we believe is responsible for Sean's amazing development.

I'm convinced this approach helped Sean a great deal because he would try to copy Lisa all the time.

However, it did lead to an unexpected change in Lisa's behaviour.

When they were three we sent them to the same mainstream nursery together a few days a week because we didn't want to split them up.

They were an incredibly close little pair and it would have broken their hearts to be separated.

But soon the teachers noticed that Lisa wasn't behaving like the other children.

Instead of running around playing she spent all her time helping Sean and effectively looking after him - it was a humbling display of love by a little girl, and it broke my heart to see them together like that.

I was so proud of my little girl for watching out for her brother, the way we'd always told her she should.

But I knew it wasn't fair to give her that burden, so we decided to send them to different nurseries. Neither liked it at first, but we knew it was for the best.

We sent them to the same primary school after doctors advised us that Sean could go to a mainstream school, but we had to explain to Lisa that he wouldn't learn as quickly as she would.

She told us in her usual forthright way that he would be fine, and that she'd help him with his school work.

She understood that they were different, but always considered him her equal.

Of course, we were apprehensive about sending Sean to school alongside children without disabilities, but his teachers were amazing and very supportive.

Even now, he can only speak in broken sentences, but they encouraged his creative side, and when he couldn't join in a lesson they'd give him something else to do like painting.

We strongly believed giving him a normal education would help him. I hated the thought of him sitting in a 'special school' not being fully stimulated or inspired.

Sean loved school and made some great friends, none of whom have disabilities.

On his 17th birthday they all went hill walking together with Paul. They are a great bunch of boys who really care about him and can see the wonderful fun side of his personality.

When you look past the Down's and see Sean as an individual, it's impossible not to enjoy his company. He loves to laugh, sing and dance.

Like so many children with this condition, he is extremely trusting and caring.

He loves TV shows like You've Been Framed or any other slapstick comedy - aurel and Hardy films are his favourite.

His primary education was such a success that we decided to try to get him into a state secondary school.

We knew this would throw up many more problems because he was more likely to be bullied as a teenager, but we wanted to give it a go and we found the education authority very supportive.

I think he was possibly the first child with Down's in the country to go to a mainstream secondary school, and as with primary school, he flourished.

I can recall only one occasion when another boy made fun of him, when he was 13, and immediately one of his classmates jumped to his defence.

I was amazed by how well they all treated him. I'd underestimated how compassionate and thoughtful children can be.

Lisa loved the fact that they went to the same school, and they'd often have lunch together.

Having her around has meant that Sean always had someone to tag along with and he never felt left out, even when it came to things that he otherwise might have had to miss.

I remember one occasion when they were 15 and Lisa was planning to go to a teenage disco at the local youth club.

A week before, she asked if she could take Sean with her. "He won't be cramping your style?" I asked tentatively.

"Not at all, Mum," she said, looking at me like I was crazy.

"Everyone loves having Sean around."

The only times I've felt really overwhelmed by it all is when Sean has been unwell.

Over the years he has been in and out of hospital because he has ear problems, which mean he has to wear hearing aids, and there have been problems with his muscle development - both side-effects of his condition.

I feel incredibly sorry for those parents who struggle to come to terms with their child having Down's.

It could well be that our experience has been so positive because of Lisa.

Having a non-disabled twin has really helped Sean to develop - the love they share has given him a unique support in a tough world, and I'm not sure he would have done nearly as well if he didn't have Lisa fighting his corner every step of the way.

Their brother Daniel has always been wonderfully supportive of him, too.

The three of them have an incredibly strong bond and I think that's partly because the other two have always known it was very important to watch out for their brother.

Our house is always full of fun and laughter and much of that is down to Sean.

He has a great sense of humour and is always cracking jokes. Of course, it's not all good all the time.

He can be a moody teenager, too, and sometimes slams his bedroom door and plays his music too loud.

He's a 17 year-old boy, after all, so we treat him like one.

He loves his collection of DVDs, and I always feel a little moved when I walk into the lounge and find him and Lisa curled up together watching one of his favourite films.

Sean is also well aware of girls - he'll often point to a pretty blonde and say: "I fancy her, Mum."

I'd like to think that one day he'll get married, maybe to someone else with Down's.

It's really important to us that he gets the chance to lead as normal a life as possible, though I don't think he'll ever be a father - to my knowledge, a man with Down's has never fathered a child.

Hopefully, one day Lisa and Daniel will be parents, and Sean will get all the fun of being an uncle because he loves children.

It could be that they are more on his wavelength. When his six-year-old cousin comes to stay, the two of them spend hours colouring in and playing in the garden together.

One thing is for certain: his dad and I want him to get his own flat in some kind of sheltered complex.

Somewhere he can feel independent but still get the help he will always need.

We'd also like him to have a job because he's said he would like to work, but we have no idea what he'd do yet.

When I look at my twins I can see the very obvious differences between them, but those are outweighed by the similarities - they share the same love of life and warm, generous spirit.

Regardless of Sean's disability, to me they will always be two little peas in a pod - and that's just the way they think of it, too.

quinta-feira, 15 de maio de 2008

Hemofilia

A Hemofilia é uma doença crónica e uma deficiência congénita no processo de coagulação do sangue. De transmissão genética, ligada ao cromossoma X, aparece quase exclusivamente nos indivíduos do sexo masculino e caracteriza-se pela ausência ou acentuada carência de um dos factores da coagulação (VIII - Hemofilia A ou IX - Hemofilia B). Por este motivo, a coagulação é mais demorada ou inexistente, provocando hemorragias frequentes, especialmente a nível articular e muscular.

As pessoas com hemofilia que não têm actividade (0%) de um dos factores VIII ou IX sangram espontaneamente e estão sujeitas a frequentes hemorragias profundas, nos músculos e nas articulações, considerando-se gravemente afectados.

As pessoas com hemofilia com 1 a 5% de actividade dos Factores VIII ou IX, estão afectadas mais moderadamente e as hemorragias são usualmente causadas por lesões. Com 5% ou mais de actividade, a hemofilia é considerada leve e muitas vezes só é diagnosticada tardiamente quando ocorre algum acidente grave ou intervenção cirúrgica.

A Hemofilia é uma deficiência hereditária.Herda-se, como se herda a cor da pele, a cor dos olhos, o som da voz, o tipo de sangue. Tudo isto se herda dos nossos pais. E as pessoas com Hemofilia herdam também de seus pais o sangue ao qual falta o Factor VIII ou o Factor IX. Na generalidade, são principalmente os rapazes que herdam este tipo de sangue. Quando a Hemofilia aparece numa família, e em 30% são casos esporádicos, pode continuar a ser transmitida de pais para filhos.

Doença de Alzheimer


A doença de Alzheimer é uma doença degenerativa que, lenta e progressivamente, destrói as células do cérebro, os neurónios, que não têm a capacidade de outras células do corpo para se regenerar. Ou seja, uma vez destruídos não podem ser substituídos. Não há cura.

A doença afecta a memória e o funcionamento mental (pensar, falar) mas pode levar a outros problemas como confusão, mudanças de humor, desorientação no espaço e no tempo, levando muitas vezes a que os doentes não consigam regressar à sua própria casa.
Não é uma doença infecciosa ou contagiosa. È uma doença terminal que provoca uma deterioração geral da saúde, do sistema imunitário, acompanhada por perda de peso, e portanto, predispondo ao aparecimento de doenças infecciosas.
“(…)Com o tempo a pessoa depende totalmente da ajuda de terceiros”.

terça-feira, 13 de maio de 2008

Mutações cromossómicas numéricas

Durante os processos de divisão celular podem ocorrer erros que conduzem quer à não disjunção de cromossomas homólogos na primeira divisão meiótica, quer uma não-disjunção de cromatídeos na segunda divisão. Resultando assim células com excesso ou um défice de cromossomas.


quinta-feira, 8 de maio de 2008

Mutações cromossómicas


Por vezes, são afectadas porções maiores do genoma, alterando partes significativas dos cromossomas, cromossomas completos, ou mesmo conjuntos de cromossomas.

Quando das alterações resultam quebras de porções cromossómicas, estas podem reorganizar-se de forma diferente. Nestes casos não ocorre alteração do número de cromossomas, mas sim alteração do seu material genético. A isto dá-se o nome de mutações cromossómicas estruturais.

domingo, 4 de maio de 2008

Mutações Génicas


As variações que ocorrem ao nível dos nucleótidos de um gene denominam-se mutações génicas.

Estas alterações podem ser devido à adição, à supressão, ou à substituição de novos nucleótidos na cadeia de ADN.

terça-feira, 15 de abril de 2008

Mutações


O corpo humano encontra-se em constantes alterações. As suas células dividem-se incessantemente, de tal forma que se calcula que bianualmente substituímos uma massa de células semelhante à massa do nosso corpo.

As divisões celulares dão-se a um ritmo elevadíssimo fazendo com que a possibilidade da ocorrência de erros seja enorme. No entanto, o organismo possui uma enorme capacidade de reparação, corrigindo quase a totalidade dessas anomalias. As alterações que o organismo não consegue reparar, designam-se por mutações.

As mutações têm diferentes impactos no indivíduo. Estas podem ocorrer num único gene ou provocar alterações na globalidade dos cromossomas do ser.

domingo, 10 de fevereiro de 2008

quarta-feira, 23 de janeiro de 2008

sexta-feira, 18 de janeiro de 2008

O DNA...



Cientistas descodificaram o genoma humano em 2000, apercebendo-se da extrema semelhança entre os seres humanos. Verifica-se que duas pessoas partilham entre si cerca de 99% do DNA.
DNA, ácido desoxirribonucleico, trata-se de uma molécula orgânica contendo todoa a informação para o desenvolvimento e funcionamento de todos os organismos vivos. A sua estrutura foi descoberta por James Watson e Francis Crick. Este organiza-se numa estrutura helicoidal crescendo em sentidos inversos. A dupla hélice do DNA encontra-se estabilizadda por pontes de hidrogénio entre as bases azotadas de cada segmento. Estas são, Adenina (A) que se liga sempre com a Timina (T) e a Citosina (C) que se liga com a Guanina (G). As bases azotadas em conjunto com um grupo fosfato e uma pentose (açúcar constituído por 5 carbonos) representam um nucleótido.
A molécula de DNA pode assumir diferentes formas de organização, entre elas os cromossomas. Estes são constituidos por uma única molécula de DNA, contendo informação necessária à regulação e correcto funcionamento do organismo vivo.

quinta-feira, 1 de novembro de 2007

the beginning of genetic mutations blogspot

Este blog foi criado no âmbito da disciplina de Área de Projecto, que decorre na Escola secundária Adolfo Portela. Irá ser constantemente actualizado por elementos da turma 12ºB que se encontram a realizar um trabalho sobre mutações genéticas e cromossómicas.
No blog irão ser constantemente adicionados "post's" relativos aos diferentes temas que o nosso trabalho irá abordar.
Com o objectivo de manter o rigor cientifico, fugindo assim ao senso comum, este blog irá contar com a contribuição de entendidos/especialistas nos diferentes temas abordados.