Tag: genetics

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Genetic Testing and the Burden of Knowing Your DNA

To jump or not to jump. (Dr. Noorali Bharwani)
To jump or not to jump. (Dr. Noorali Bharwani)

You have seen the commercials about genetic testing. I am sure you have been tempted to get the test done for yourself. Then you ask, “How much do I want to know about the unknown?” Well, read-on and find out.

Genetic testing involves examining your DNA. DNA is the chemical database that carries instructions for your body’s functions. Genetic testing can reveal changes in your genes that may cause disease. Remember, genetic testing is not perfect.

Different types of genetic testing are done for different reasons. There are at least seven different reasons why DNA test would be indicated. These are: diagnostic testing, presymptomatic and predictive testing, carrier testing, pharmacogenetics, prenatal testing, newborn screening, and preimplantation testing.

A positive test does not always mean you will develop a disease. A negative result does not guarantee you won’t have a certain disorder. If you plan to take the test then you should know what you plan to do with the results.

What are the advantages of genetic testing?

  1. Genetic testing plays a vital role in determining the risk of developing certain diseases as well as screening and sometimes medical treatment.
  2. With a positive result, in some cases, you can make lifestyle changes that may reduce your risk of developing a disease, even if you have a gene that makes you more susceptible to a disorder.
  3. Positive results may help you make choices related to treatment, family planning, careers and insurance coverage.
  4. You may choose to participate in research or registries related to your genetic disorder or condition.

What are the disadvantages of genetic testing?

  1. Genetic testing can have emotional, social and financial risks.
  2. It may affect rest of your family. Discuss with them before you go for the test. Find out how your family might respond to your test results and how it may affect them.
  3. Find out if it is going to affect your work.
  4. What about your life insurance policy – how would that be affected?
  5. A negative result does not mean you don’t have the disorder.
  6. Sometimes it can be difficult to distinguish between a disease-causing gene and a harmless gene variation.

It will be wise to get genetic counseling before and after you get the test. This may be in the form of your doctor, medical geneticist or genetic counselor. This will help you understand what the results mean for you and your family.

To summarize, genetic testing has potential benefits whether the results are positive or negative. Your test results can provide a sense of relief from uncertainty and help you make informed decisions about managing your health.

A positive result can encourage you to take preventive measures. Some test results can help people make decisions about having children. Screening in newborns can identify genetic disorders early in life so treatment can be started as early as possible.

Your family physician will always provide you care that is within the limits of his/her knowledge. Your physician will ask for a consult with a specialist in genetics if appropriate. Your physician will respect your right to make autonomous decisions in looking after your health.

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Six Distinct Types of Inherited Disorders Affect Several Parts of the Body

Rabbit preparing to cross the road. (Dr. Noorali Bharwani)
Rabbit preparing to cross the road. (Dr. Noorali Bharwani)

The title of this column may sound strange and you may not have heard of this condition before. That is because it is not a common problem. It is called Ehlers-Danlos syndrome (EDS). EDS is known to affect men and women of all racial and ethnic backgrounds.

EDS is a group of inherited connective tissue (bones, joints, skin) disorders, caused by various defects in the synthesis of collagen. Collagen is the main structural protein that gives strength to various connective tissues in animals. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25 to 35 per cent of the whole-body protein content.

Individuals with EDS have disorders marked by extremely loose joints, plastic like loose skin that bruises easily, brittle bones and easily damaged blood vessels. There are six distinct types of EDS currently identified. Each type is thought to involve a unique defect in connective tissue, although not all of the genes responsible for causing EDS have been found.

How common is Ehlers-Danlos syndrome? According to some literature, the exact numbers are difficult to estimate. It is believed the combined prevalence of all types of this condition may be about one in 5,000 to 40,000 individuals worldwide. There are many sub-groups of the condition that are hard to estimate.

First description of EDS was by Hippocrates in 400 B.C. In 1657 a Dutch surgeon noted a case history of a boy with very lax skin. The first association of very mobile joints to skin was published in 1892 in Moscow by A.N. Chernogubov. In 1901, Edvard Ehlers and in 1908 Henri-Alexandre Danlos described different disorders involving joints and skin with bruises. In 1936, the disorder was named Ehlers-Danlos syndrome.

Treatment is based on the symptoms. Unfortunately, there is no specific cure. Individuals with EDS generally have a normal life span. Their intelligence level is normal. Those with the rare vascular type of EDS are at greater risk of rupture of a major organ or blood vessel. These individuals have a high risk of sudden death.

What do we know about genes and mutation?

A gene is a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring. Mutation is a natural process that changes a DNA sequence. And it is more common than you may think.

As you know genetic disease is caused by an abnormality in an individual’s genetic material. The abnormality can range from minuscule to major. It occurs from a discrete mutation in a single base in the DNA of a single gene to a gross chromosome abnormality involving the addition or subtraction of an entire chromosome or set of chromosomes. Sounds complicated?

Some genetic disorders are inherited from the parents, while other genetic diseases are caused by acquired changes or mutations in a preexisting gene or group of genes. Mutations occur either randomly or due to some environmental exposure. A gene mutation is a permanent change in the DNA sequence that makes up a gene. Well, this is a short introduction to genetics.

If you have a family history of EDS and are planning to have children then you should seek genetic counseling. You can learn more about EDS from the Ehlers-Danlos National Foundation website.

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Significance of BRCA genes in ovarian cancer.

International symbol of breast cancer awareness. (iStockphoto)
International symbol of breast cancer awareness. (iStockphoto)

First, it was Angelina Jolie, who had a double mastectomy because of increased genetic risk of breast cancer due to the presence of BRCA gene. The presence of BRCA gene also increases the risk of ovarian cancer. We know that if you have a family history of ovarian cancer then the risk of ovarian cancer increases amongst women in that family.

Take for example the recent announcement that Pierce Brosnan’s daughter Charlotte Emily died of ovarian cancer at age 42. Brosnan is a former James Bond star whose first wife, Cassandra (Charlotte’s mother), was also killed by the same disease in 1991 when she was 43. I am not sure if Charlotte Emily’s BRCA status is known.

There are two types of BRCA genes known as BRCA1 and BRCA2. BRCA is an abbreviation for breast cancer. These genes are tumour suppressor genes and once they undergo changes (mutation), their capacity to normally prevent cancer from developing is lost. It is now known that women found to have mutations in the genes have a very high risk of developing breast and ovarian cancers.

The genetic mutations are not common. About one in 500 to one in 1,000 individuals will carry a mutation or a gene change in one or another of these genes. It generally occurs amongst people who tend to stay together and don’t have offspring with people from other types of ethnicities. Experts say these mutations tend to stay within one group of individuals.

What distinguishes BRCA1 and BRCA2 genes is where they’re located in the chromosomes. There are also slight differences in terms of the types of cancers associated with the two genes.

The main difference in the two genes is that carriers of the BRCA1 gene mutation have a slightly increased risk of ovarian cancer compared to those with BRCA2. It is also known that carriers of BRCA2 genes have risks of different types of cancers, including pancreatic cancer and melanoma.

For ovarian cancer, women with a mutated BRCA1 gene have a 25 to 65 per cent lifetime risk of developing the disease. Those with a mutated BRCA2 gene have a 15 to 20 per cent chance of developing ovarian cancer.

For men, it is little different. For men with the BRCA2 mutation, there’s an increased risk of both prostate and breast cancers.

Who can ask for BRCA genetic testing?

There has to be a strong family history of cancer. The cancer must have occurred in young ages within the family and if you are a member of ethnic groups known to be affected then you would be eligible. If you don’t meet the criteria but still want to be tested then you can go south of the border and get yourself tested for about $3,000.

Early detection of breast cancer has dramatically changed the prognosis of the disease. We cannot say the same thing about ovarian cancer because we do not have any tests for early detection.

Each year, about 2400 Canadian women are diagnosed with ovarian cancer. Sadly, 1700 women with the disease die each year. In North America, ovarian cancer is the second most common gynecologic malignant disease and is the leading cause of death among women with gynecologic cancer.

More than 60 per cent of the women are in advanced stage when first diagnosed. Their five year survival rate is less than 30 per cent. Their prognosis is poor and they have very few treatment options. Some studies have reported higher survival rates of greater than 90 per cent in women with stage one disease. Only 25 per cent of the women are diagnosed early.

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Genetically Engineered Frankenfish is Considered Safe

A fish jumping out of the water. (Hemera/Thinkstock)
A fish jumping out of the water. (Hemera/Thinkstock)

Have you heard of “frankenfish”? It is a Frankenstein fish. Yuck, right? Well, have no fears. A media report including one in the Washington Post (December 21/2012) says, “Federal health regulators say a genetically modified salmon that grows twice as fast as normal is unlikely to harm the environment, clearing the way for the first approval of a scientifically engineered animal for human consumption.”

The Canadian Press reported on January 4, 2013, “Canadian ‘frankenfish’ moves closer to FDA approval for human consumption.”

In the U.S., the Food and Drug Administration (FDA) said the fish is unlikely to harm populations of natural salmon, a key concern for environmental activists. The AquaAdvantage salmon has been called by the critics as frankenfish. They see the development of frankenfish unethical and worry it could cause human allergies and eventually destroy the natural salmon population if it escapes and breeds in the wild.

FDA has said in the past that animals that are cloned are safe to eat. But frankenfish is not a clone. The DNA has been changed to produce a desirable effect. There is added growth hormone from the Pacific Chinook salmon that allows the fish to produce growth hormone all year long. Typical Atlantic salmon produce the growth hormone for only part of the year. The company says frankenfish will have the same flavour, texture, colour and odour as the conventional fish.

This is only one example of genetically altered food. There are many other foods which have been genetically changed. The Health Canada website (http://www.hc-sc.gc.ca/) says, “Health Canada conducts a thorough safety assessment of all biotechnology-derived foods to demonstrate that a novel food is as safe and nutritious as foods already on the Canadian marketplace.” Internationally, more than 10 species specific consensus documents have been developed, including for corn, soybean, wheat, rice, canola and sugar beet to ensure safety of these foods for human consumption.

As of 2012, Health Canada has approved over 81 genetically modified foods for sale in Canada. No applications have been turned down as long as they meet Health Canada’s strict guidelines. According to Wikipedia, commercial sale of genetically modified foods began in 1994, when Calgene Inc. first marketed its Flavr Savr delayed ripening tomato. Since then the technology has been used in different areas. There are organisms which have been genetically engineered and there are crops which have undergone genetic changes.

Some fruits and vegetables have been genetically changed to prevent disease in the crops. For example, Papaya has been genetically modified to resist the ringspot virus. Today, 80 per cent of Hawaiian papaya is genetically engineered. As of 2005, about 13 per cent of the zucchini grown in the US was genetically modified to resist some viruses. Most vegetable oil used in the US is produced from genetically modified crops. We can go on. There are many such examples. No reports of ill effects have been documented in the human population from genetically modified food.

Looks like genetically modified food is here to stay. And we are eating it every day.

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