Sunday 15 April 2012

Genetic Disorders and Prenatal Testing

There are hundreds of genetic disorders that have been diagnosed and have also been linked to specific mutations in the DNA. There are some common genetic disorders that occur more frequently than others; for example because "people in an ethnic group often share certain versions of their genes, which have been passed down from common ancestors; therefore if one of these shared genes contains a disease-causing mutation, a particular genetic disorder may be more frequently seen in the group" (http://ghr.nlm.nih.gov/handbook/inheritance/ethnicgroup). This can be seen in genetic disorders such as "sickle cell anaemia, which is more common in people of African, African-American, or Mediterranean heritage" (http://ghr.nlm.nih.gov/handbook/inheritance/ethnicgroup). There are also other common disorders such as cystic fibrosis, Down's syndrome, haemophilia and colour blindness.

I will do short introductions on what down 's syndrome, haemophilia and cystic fibrosis are, and then discuss the ethical sides of  the diagnostic testing that is available to pregnant women and also the ethics of abortion.

Down's Syndrome: "someone with Down's syndrome has an extra copy of chromosome 21 in the cells of their body. This is known as trisomy 21 (trisomy means there are three copies of a chromosome - in this case, chromosome 21). Because there is an extra chromosome 21, there is extra genetic material in the body" (http://www.patient.co.uk/health/Pre-natal-Screening-and-Diagnosis-of-Down''s-Syndrome.htm). It also explains on that website the typical features of down's syndrome, but also explains that "anyone can have a baby with Down's syndrome but a woman's risk increases as she gets older" (same website).

Cystic Fibrosis: occurs in places where mucus is produced and is caused by a mutation in the CFTR gene, which codes for the CFTR protein. The CFTR protein performs in a complicated mechanism that regulates the movement of chloride ions, sodium ions and water movement in and out of the mucus. When the mucus becomes too sticky for the cilia (hairs on epithelial cells) to move the mucus to where it needs to be (i.e. in the bronchus up to the mouth) the water needs to be drawn into the mucus to make it less viscous but when the CFTR is no longer present the chloride ions cannot get into the mucus to draw the water in via osmosis. This leads to blockages and damage to the lungs, reproductive system and other mucus dependent areas of the body. Sadly, because of the bacterium getting caught in the mucus, it is then dragged down into the lungs and destroys the alveoli and bronchioles, reducing the surface area and eventually suffocating the sufferer. For a more detailed explanation see http://www.patient.co.uk/health/Cystic-Fibrosis.htm which explains the effects on the other parts of the body as well, very interesting genetic disorder.

Haemophilia: (2 types; A and B, which only vary due to "problems with different clotting factors) is a genetic (inherited) condition that affects the blood’s ability to clot, normally, if you cut yourself, proteins called clotting factors combine with blood cells called platelets to make the blood sticky. This makes the bleeding stop eventually. However, in haemophilia, there are not as many clotting factors in the blood as there should be. Therefore, someone with the condition will bleed for a longer time than usual" (http://www.nhs.uk/conditions/Haemophilia/Pages/Introduction.aspx). This means that people with haemophilia can be subjected to a greater volume of blood loss (both internal and external) than should normally occur which can be dangerous for the person with the disorder. It is also interesting that it "almost always occurs in males" (http://www.nhs.uk/conditions/Haemophilia/Pages/Introduction.aspx).

There are a number of  tests that can be carried out to ascertain whether your child will have a genetic disorder; "prenatal testing provides information about your baby's health before he or she is born and, based on screening test results, your doctor might suggest diagnostic tests. Diagnostic tests confirm or rule out health problems in you or your baby" (http://www.nlm.nih.gov/medlineplus/prenataltesting.html).

1) Amniocentesis: carried out at 15-17 weeks of pregnancy where a needle is inserted into the amniotic fluid to collect cells that have fallen off the embryo which are then tested for known genetic disorders. It is "usually only offered to women when there is a significant risk that their baby will develop a serious condition or abnormality. This is because the procedure is quite invasive and has a small associated risks of miscarriage; estimated to be 1 in 100" (http://www.nhs.uk/conditions/Amniocentesis/Pages/Introduction.aspx).

2) Chorionic Villus Sampling: this is where placental tissue is removed (around 8-12 weeks) via "transabdominal CVS-a needle is inserted through the abdomen, or, transcervical CVS – a tube is inserted through the cervix (the neck of the womb)" (http://www.nhs.uk/conditions/Chorionic-Villus-sampling/Pages/Introduction.aspx). "The risk of CVS causing complications, such as miscarriage or birth defects in the baby, is higher if it is carried out before week 10 of the pregnancy" (as above).

So what are the implications of getting results from these tests? Well, if the results are negative then the family will probably decide to continue with the pregnancy as intended, but what if they come back positive?

1) The couple will receive guidance from their GP and will be given access to a whole host of people who can help them to make their decision and prepare for the child or to have an abortion, but either way, it will be an informed decision, that is best for everyone involved.
2) An argument that is often used is from those who believe in life beginning at conception, so they would say that an abortion is not the correct option, since that child now has a life ahead of him.
3) Others would say that life begins at birth and that the child is not conscious in the womb, so would argue against number three, but both arguing about human rights and when they are granted.
4) It also depends on the severity of the genetic disorder because if it is haemophilia then there is a good chance that the child will have a long life ahead of him that he can prosper in. But with cystic fibrosis it is very difficult for the child because of the treatments they must undergo regularly and also the suffering that they go through.

Please feel free to add to the list by leaving a comment and starting a discussion!

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