Reciprocal Translocations

A translocation is the term used to describe a rearrangement of chromosome material between two or more chromosomes. There are two main types of translocations; reciprocal and Robertsonian translocations. In this blog piece, I will discuss reciprocal translocations.

In each of our body cells (excluding our egg or sperm cells) inside the nucleus we have 23 pairs of chromosomes. They are numbered 1 to 22 in descending order of size and the remaining pair of chromosomes are our sex chromosomes; XX for females and XY for males. A reciprocal translocation is where part of one chromosome breaks and exchanges with part of another chromosome, which has also broken off. Said another way, two chromosomes break and these broken pieces swap and join back together. When no genetic material is lost, this is said to be a balanced reciprocal translocation. Reciprocal translocations can involve any of the chromosomes.

Carriers of a balanced reciprocal translocation may not even be aware that they are carrying a chromosomal anomaly. Depending on the location of the break, if no interruption of the genetic information in the DNA code occurs, a carrier of a balanced translocation will have no symptoms and will not affect their development or health. However occasionally where the chromosomes break, if this is in the middle of an important gene, for example, the person may have some associated health issues. Most translocations are spontaneous, meaning, they occurred in the egg or the sperm that went on to create a person. However sometimes translocations can be inherited.

Balanced reciprocal translocation carriers are at risk of having chromosomes in their eggs or sperm with genetic material gained or lost and this could result in a pregnancy that has an unbalanced reciprocal translocation. Having extra or missing bits of chromosome can cause a wide variety of health problems including mild to severe health problems and developmental delay.

If someone is at risk of being a carrier of a balanced reciprocal translocation, they can have a genetic test examining their chromosomes. This test is called a karyotype and the scientists in the laboratory will be able to see if and where a translocation has occurred. A more detailed chromosome test called a microarray may also be ordered to see exactly where the breakpoints are and to see if any genetic material has been added or lost.

When a partner in a couple has a balanced translocation they may experience infertility or recurrent miscarriages. In some cases it may be possible to have Non Invasive Prenatal Testing (NIPT), which is a blood test on the pregnant mother from 10 weeks gestation, to see if the pregnancy has a translocation. In some cases NIPT is not possible. If this is the case, an invasive test during the pregnancy such as a chorionic villus sampling (CVS) or amniocentesis may be performed to examine the baby’s chromosomes.

Couples presenting for genetic counselling due to a reciprocal translocation can be challenging from a psychosocial point of view as well. Having long periods of infertility or miscarriage after miscarriage can be very taxing on couples. IVF is one technique that couples can utilize to increase their chances of having a baby. Other options would include donor egg, sperm or embryos or adoption.
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What is Genetic Counselling?

What is Genetic Counselling?

As a genetic counsellor, “what is genetic counselling?” is the most common question I am asked. Most people are not aware of ever having met a genetic counsellor and do not know what genetic counselling is or what genetic counsellors do. Genetic counselling is a relatively new profession and there is quite a bit of controversy surrounding our professional name and whether it is the best description of what our role entails.

Genetic counselling is aimed at providing information and support to people who have or are at risk of genetic disorders. A genetic counsellor is a postgraduately trained health care professional who can identify your risk factors and provides clear information about the chances of being affected by a specific genetic condition. Usually when you have a health related question or concern you go and see a General Practitioner. If this issue is genetics related, you may be referred to see a genetic counsellor.

Genetic counsellors are health care professionals who integrate their knowledge on medical genetics, basic science and counselling theory with their skills in genetic risk assessment and communication to educate their clients on a diverse set of genomic or genetic indications. They help people to understand their genetic contributions to disease. These professionals are employed in diverse settings such as public hospitals, community health centres, IVF clinics, university research facilities and private medical centres. Genetic counsellor usually have an undergraduate degree in science, nursing, social work, teaching or psychology followed by a two years masters course in genetic counselling. Once qualified and practicing in the field, genetic counsellors usually undergo an accreditation process to become certified.

Genetic counsellors investigate the genetic history of your family, arrange for appropriate genetic testing, interpret the details about your disorder, evaluate the inheritance patterns and review the options available to treat your medical condition. They will also liaise with your general practitioner and other medical specialists in regards to your results.

Some common examples of when you may meet with a genetic counsellor include:
• You have undergone routine pregnancy screening tests and have received a high risk result
• You have a strong family history of a particular condition and would like information about your risks and about genetic testing
• You have just had a diagnosis of breast or ovarian cancer and your medical oncologist would like to know whether you have an inherited reason for your history of cancer
• You have a child with a recessive condition like cystic fibrosis and would like to discuss carrier testing and options for following pregnancies

It is a rewarding and fulfilling professional and I love doing my job. There is an international shortage of genetic counsellors so it might just be a great new vocation for you too.

Happy Friday

Matt Burgess
Consultant Genetic Counsellor

Genetic Condition – HFE – Hereditary Haemochromatosis

Genetic Condition – HFE – Hereditary Haemochromatosis

HFE – Hereditary Haemochromatosis is a common genetic condition in which sufferers have an abnormally high level of iron uptake into various organs in their body. It is an iron overload disorder. HFE – Hereditary Haemochromatosis was also known as Bronze diabetes in the past due to the colour that an affected person may turn without treatment. Early symptoms include weakness, fatigue, abdominal pain and weight loss. If left untreated, HFE – Hereditary Haemochromatosis can lead to skin discolouration, diabetes and heart problems.

 

Inheritance / genetic counselling

HFE – Hereditary Haemochromatosis follows an autosomal recessive pattern of inheritance. A personal affected with this condition has two faulty copies of their HFE gene; one inherited from their mother and the other from their father. If an affected person’s parents had one working copy of HFE and one copy with a mutation, they are referred to as being a carrier of HFE – Hereditary Haemochromatosis. A person with HFE – Hereditary Haemochromatosis can only pass on a faulty copy of the HFE gene meaning that all of their children will either be carriers if they inherit a working copy of the HFE gene from their other parent or at risk of developing the condition if they inherit a faulty copy of the HFE gene from each parent. Siblings of a person with HFE – Hereditary Haemochromatosis usually have a 25% risk of also having the condition, however if their parent also has the condition then 50% of their children are at risk.

 

Molecular genetics

This condition is due to a mutation in the HFE gene, which is located on the short arm of chromosome 6 at location 6p22.2. A gene is made of DNA and DNA is made of four chemicals referred to as bases (A, G, C & T). These bases combine together in a pattern to code for one of 20 amino acids. Amino acids strung together form a protein. There are three common mutations in the HFE gene; C282Y, H63D and S65C.

About 60 – 90% of people with two copies of the C282Y mutation will develop iron overload in their lifetime, whereas only about 5% of people with a C282Y and H63D combination will develop the condition. About 1% of people with two copies of H63D will go onto having iron overload.

 

Prevalence

HFE – Hereditary Haemochromatosis is the most common genetic condition in Australia and one of the most common genetic conditions in Caucasians. HFE – Hereditary Haemochromatosis is uncommon in people with African and Asian decent. HFE – Hereditary Haemochromatosis is more common in men than women.

 

Management

The most common treatment for HFE – Hereditary Haemochromatosis is blood letting to reduce iron levels in the blood.

 

Differential diagnoses

Not everyone with iron overload will have HFE – Hereditary Haemochromatosis. Other types of Hereditary Haemochromotosis include Juvenile hereditary haemochromotosis (also known as hereditary haemochromotosis type 2) and TFR2 – Hereditary Haemochromatosis.

 

Resources:

http://www.americanhs.org/

www.haemochromatosis.org.au

www.haemochromatosis.org.uk

http://www.genetics.edu.au/publications-and-resources/facts-sheets/fact-sheet-47-hereditary-haemochromatosis