Genetics
A gene is a length of DNA forming part of a chromosome – in humans there are about 20,000-25,000 different genes arranged among the 23 pairs of chromosomes. Genes contain the code to make proteins, which are involved in the development and functioning of body organs and systems. Proteins are essential to life and have many functions in the body. Genes are also units of heredity by which characteristics are passed from one generation to next.
There have been significant and groundbreaking developments in the field of genetics and as with other medical conditions, there has been gene mapping for the various types of arthrogyrposis leading to a greater understanding. This now gives people a better chance of a specific diagnosis of a particular condition they have and can give them a clearer indication of what inheritance pattern to expect. Sometimes, the disorder is caused by a single gene, where the parent has passed on a single abnormality in the genetic information to the child. If this is so, the disorders can fall into any of the three groups:
- Autosomal dominant where a single, abnormal gene on one of the autosomal chromosomes from either parent can cause certain disease or disorder. Usually, one parent must have the abnormal gene in order for the child to inherit the disease.
- Autosomal recessive is when an abnormal gene from each parent is required to cause the disease or disorder. If the parent only has a single copy they are a ‘carrier’ but since the gene in question is recessive (hidden) they do not exhibit the disease or disorder themselves. When both parents are carriers they children have a one in four chance of inheriting both defective copies, a one in two chance of being a carrier (heterozygous for the defective gene) and a one in for chance of being neither affected nor a carrier.
- X-linked disorders are those in which the defective gene lines on the X sex chromosome. Each person inherits the sex chromosomes along with the other 22 pairs of non-sex chromosomes – if its two copies of the X chromosome then the child is female; an X and Y makes a male. X-linked disorders are most common in males as there is no second X chromosome carrying a normal copy of the gene to compensate.
More detailed information on inheritance patterns can be found at the website of the Genetic Interest Group www.gig.org.uk
There are many reasons for people wanting to seek genetic counselling which could include:
- giving birth to a baby with arthrogryposis
- no specific diagnosis ever given – only the term ‘arthrogryposis’ has been used
- a diagnosis of Distal Arthrogryposis has been given but no actual type specified
- wanting to have more children
- an affected child is approaching adulthood.
When you meet with the clinical geneticist or genetic counsellor, or sometimes both, you will have the opportunity to spend time discussing your concerns and will be asked for information about your personal medical history and that of your family. A family tree will be drawn up which can give invaluable information and the consultant is likely to ask many questions about your pregnancy.
Whatever information you can give will be a great help – the more detail, no matter how trivial it may seem will aid them to get a better picture much sooner.
It is going to an emotional time so we advise that you make sure you ‘prepare’ for the appointment by:
- Get yourself a notebook, pen, camera – make sure you note everything down
- Think about your pregnancy – did your baby move, were you ill or have a high fever, use a jacuzzi or hot tub regularly? Did you have a bump or knock to the abdomen? Or other complications such as bleeding, amniotic leakage?
- Be a ‘detective’ and ask your close family members (mother, father, grandparents if you can) about their parents, siblings and others. Very often anecdotal evidence proves to be the best way to find out if there is a history of joint problems, clubfoot, etc.
- Don’t be afraid to ask questions – remember this is your opportunity to ask about what has happened – list them down and don’t worry that you don’t know the correct medical terms.
If you can, for the meeting with the genetic team, take someone with you to make notes. You will be given a lot of technical information and it is very easy to forget things once you are in the session - afterwards you will want to know more and do further research of your own, if only to give you peace of mind. Also, ask if your GP will be getting a letter that will be a summary of the main points from the discussion, this too can help.
For more advice and local support during a pregnancy contact The NCT (known as the National Childbirth Trust) Telephone: 0300 330 0772 or visit www.nctpregnancyandbabycare.com
If you do have to think about making a decision on screening and/or testing in pregnancy then contact Antenatal Results & Choices - ARC for help. Telephone 020 7631 0285 or visit www.arc-uk.org