Genetics Explained

About genes
Your genes are a set of instructions for the growth and development of every cell in your body. For example, they determine characteristics such as your blood group and the colour of your eyes and hair.

However, many characteristics aren't the result of genes alone – environment also plays an important role. For example, children may inherit "tall" genes from their parents, but if their diet doesn't provide them with the necessary nutrients, they may not grow very tall.

Chromosomes
Genes are packaged in bundles called chromosomes. In humans, each cell in the body contains 23 pairs of chromosomes – 46 in total.

You inherit one of each pair of chromosomes from your mother and one from your father. This means there are two copies of every gene in each cell, with the exception of the sex chromosomes, X and Y. The X and Y chromosomes determine the biological sex of a baby. Babies with a Y chromosome (XY) will be male, and those without a Y chromosome will be female (XX).

This means that males only have one copy of each X chromosome gene, rather than two, and they have a few genes found only on the Y chromosome that play an important role in male development. 

Occasionally, individuals inherit more than one sex chromosome. Females with three X chromosomes (XXX) and males with an extra Y (XYY) are normal, and most never know they have an extra chromosome.

The whole set of genes is known as the genome. Humans have about 21,000 genes on their 23 chromosomes, plus 37 genes in their mitochondria.

Mitochondria are small structures inside cells that allow the cell to get energy from sugar and fat, and they're only passed on within eggs. This means mitochondrial DNA is only inherited from mothers.

Genetics of vEDS by Duncan Baker, Lead Scientist for Musculoskeletal and Respiratory Genomics Specialist Services.

DNA

Genes are made up of deoxyribonucleic acid (DNA). DNA is a long molecule made up of a combination of four chemicals: adenine, thymine, cytosine and guanine, represented as letters A, T, C and G. These "letters" are ordered in particular sequences within your genes. They contain the instructions to make a particular protein, in a particular cell, at a particular time.


Proteins are complex chemicals that are the building blocks of the body. For example, keratin is the protein in hair and nails, while haemoglobin is the red protein in blood.


Collagen

Collagen is the major structural protein of connective tissue and therefore one of the most abundant structural proteins in our body. Collagen is a major structural component of blood vessel walls, the bowel, lungs uterus tendons and also our skin. In addition, collagen plays a large and fundamental role in wound healing after an injury to the skin.


COL3A1 gene is the instruction for making collagen type III a tough fibre-like protein that makes up a third of our body protein. When this gene is altered, it causes a lack or deficiency of this collagen making the connective tissue less effective, particularly in skin, lung, uterus, intestine and the vascular system.


Genes and medical conditions

As well as determining characteristics such as eye and hair colour, your genes can also directly cause or increase your risk of developing a wide range of medical conditions. Although not always the case, many of these conditions occur when a child inherits a specific altered (mutated) version of a particular gene from one or both of their parents. 


There are also many conditions that aren't directly caused by genetic mutations. These conditions can occur as the result of a combination of an inherited genetic susceptibility and environmental factors, such as a poor diet, smoking and a lack of exercise.


Genetic testing

A genetic test is usually done using a sample of your blood or saliva.


Genetic testing can be used to find out whether you're carrying a particular genetic mutation that causes a medical condition. This can be useful for a number of purposes, including:

 

  • diagnosing certain genetic conditions such as vascular EDS
  • predicting your likelihood of developing a certain condition
  • determining if any children you have are at risk of developing an inherited condition

 

Genetic testing can also be used to find out whether a foetus is likely to be born with a certain genetic condition. A sample of cells from the womb is extracted and tested.  

Genetic Testing

What is genetic testing?
Genetic testing – sometimes called genomic testing – finds changes in genes that can cause health problems. It's mainly used to diagnose rare and inherited health conditions such as vascular EDS.

Some people with vascular EDS are diagnosed on the basis of subtle signs in their physical appearance, together with their medical history and a genetic test. Many people who do not have vascular EDS can have some of these features as some are common in the general population. Also, not everyone with a confirmed diagnosis of vascular EDS has all of the typical features.

Who can have a genetic test on the NHS?
You need to be referred for genetic testing by a doctor. 

Talk to your hospital specialist about whether testing is right for you.

Is genetic testing free on the NHS?
Genetic testing is free on the NHS if you are referred for it by a hospital specialist.

You will generally only be referred if you have a suspected genetic health condition or if you have a particular type of cancer.

Having a genetic test
A genetic test is usually done using a sample of your blood or saliva, and in some cases a skin biopsy.

The sample of blood, saliva or body tissue is sent to a genetic testing laboratory to be analysed.

Getting the results
You'll be told when to expect the results of your test. Currently, it takes approximately 4 months and in some instances results are available sooner therefore we advise to stay with the NHS for genetic testing.

The results from the test may show:
  • you have a change in your genes which is known to cause a health condition
  • you do not have a change in your genes which is known to cause a health condition
  • it's not clear what the results mean for your health (but doctors may have a better understanding of the results in the future), this is referred to as a Variant of Uncertain Significance (VUS). 
After you get your results, you may be referred to a genetic counsellor to help you understand what they mean for you and your family.

Priority genetic testing
Priority testing is available for the most urgent clinical work if there is a suspicion of vascular EDS and the patient is:
  • pregnant women undergoing prenatal diagnosis;
  • where rapid genetic testing may alter clinical treatment or decision making regarding any planned surgical operation.
Diagnostic confirmation
If you receive a confirmed diagnosis of vascular EDS, you should contact us to let us know, we can provide you with all the resources available through the VEDS Support Programme.

We can also facilitate a referral to the EDS Service, a highly specialised service commissioned by NHS England for individuals and families who are suspected to have complex Ehlers-Danlos Syndrome (EDS). Established in 2009 the service runs two specialist clinics for patients based at Sheffield Northern General Hospital and the Northwick Park & St Mark's Hospitals in London.
Genetic Clinics

Can I have private genetic testing?

Private genetic testing involves the same genetic testing process, but you will have to pay for it instead of the NHS. It can often be delivered by clinicians who work both in the NHS and for a private practice, but not every clinician works for a private practice – there is a smaller pool of clinical expertise in private practice.


Many of the elements of the process are slow, and this is mostly not because of NHS resource problems, or waiting times, but because the process of making a genetic diagnosis takes time. You will probably be able to access genetic testing sooner, but you might not get as good an outcome.


In NHS Regional Genetics Services, patients suspected of vascular EDS might be referred to the EDS National Diagnostic Service who are experts in the rarer types of EDS, or your clinician might consult with them. If that expert does not provide private services, then you might lose out on that specific expertise by going privately.


There is also an issue with continuity. When it is working well, the NHS should function as a single complete system, where one clinician can refer you to the most appropriate clinician to treat them. Before entering into private genetic testing, you should make sure you understand what the next steps for you will be, and whether the NHS will continue your treatment.


Please note we do not have details of any private testing or consultants who offer appointments and medical services outside of the NHS.


What is direct-to-consumer genetic testing?

Direct-to-consumer genetic tests are genetic tests that are marketed directly to you as a consumer. You can order these online or by post, complete at home and then send away for analysis. Direct-to-consumer genetic tests can provide you with some information about your genetics but they are not tailored to you.


These tests are not designed to diagnose a medical condition and should not be used as a substitute for visiting your specialist if you are at all concerned about vascular EDS. It is also important to note that they are not designed for use on children.


If you have any concerns about vascular EDS speak to your specialist.

Genetic Counselling

Genetic Counselling
If you're offered a genetic test, you may be referred to a genetic counsellor to help you think through what the test means for you and your family.

A genetic counsellor can help you understand:
  • the risks and benefits of you having a genetic test
  • the potential results of your test and what they mean
  • how your family members may be affected if the test shows a serious health condition runs in your family
  • the risk of you and your partner passing on a health condition to your children
  • your options if you have a child with an inherited health condition and you do not want your next child to inherit it
A genetic counsellor can also direct you to relevant patient support groups.
What is the role of a Genetic Counsellor?
The role of a genetic counsellor includes analysing a patient's family history, assessing the chance of inheriting or passing on a condition, arranging genomic tests and communicating results, assisting with family communications, and managing the psychosocial impacts of genetic risk or results.

Genetic counsellors help people across a range of circumstances. For example, they may provide advice to couples who have a higher chance of passing on an inherited condition, support families where a child has been diagnosed with a condition or arrange predictive testing when someone is at high risk for disease based on their family history.

Increasingly, genetic counsellors are also working in a range of other roles. For example, as researchers, policy developers, educators of the wider healthcare workforce, or various subject experts.

In any of these settings, genetic counsellors use their skills as expert communicators and patient advocates to support the safe and effective delivery of genomic healthcare.

In the UK, there are approximately 300 genetic counsellors, the vast majority work in the NHS as part of a team alongside doctors, clinical laboratory scientists, nurses, midwives and other healthcare professionals. They also work very closely with clinical geneticists. Clinical geneticists are qualified to diagnose genetic conditions.

Last Updated: November 2024

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Vascular EDS is caused by a mutation in the COL3A1 gene.

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