Siblings Day - Genetic or Hereditary?
Table of Contents
For Siblings Day, we'll be looking at whether you might share more than you think with your brothers and sisters (and we aren't talking about the things they "borrow" behind your back!). Do you know the difference between a genetic and a hereditary condition?
Today is the 10th of April, and also an internationally-recognised day: Siblings Day!
Whilst it’s not quite on the scale of Mother’s Day or Father’s Day, it’s still celebrated by people all over the world (so yes, you can use it as an excuse to get your brother or sister to run to the garage for a bar of chocolate. Because, y’ know, they’re blessed to have a sibling).
Like it or not, you share many things with your siblings (even if you don’t want to… or even know about it). When you have the same set of biological parents, you also share some DNA; around 50% to be exact. It’s all in your genes. However, there are some cases where one sibling inherits something from the parents where the others don’t. Is this genetic too? Or is it hereditary? For Siblings Day this year, we’re going to look at the difference between the two terms and why they’re so often confused.
Genetic and hereditary, is there a difference?
Yes! Although the two terms are often (and can sometimes) be used interchangeably, there is a slight difference between something that’s genetic and something that’s hereditary. However, hereditary conditions and diseases are often genetic in nature, so in many cases, there’s a large overlap between the terms.
What does hereditary mean?
Hereditary is defined in the Cambridge Dictionary as:
'(of characteristics or diseases) passed from the genes of a parent to a child'
Simply speaking, this means that a hereditary condition or disease is something that’s characteristically passed from one generation to another. Other hereditary traits include distinguishable family features, so if many members of your biological family have a similar nose etc., this might be classed as a hereditary feature.
When it comes to hereditary conditions, there’s no guarantee that something will be transferred from parent to child, but it does mean that there’s an increased risk of it happening. Let’s look at an example of a hereditary condition.
You might remember that a few weeks ago, we wrote about twins Molly and Ellie for rare disease day. Ellie has been diagnosed with cystinosis, a rare condition involving the amino acid, cysteine. Whilst it’s a hereditary condition, her twin sister Molly doesn’t suffer from it at all. But how can this be when both girls have the same parents?
Cystinosis is an autosomal recessive condition. This means that a child has a 1 in 4 chance of being born with the disease, as they have to inherit an affected gene from each parent, so where Ellie suffers from the condition, Molly is unaffected. However, due to the hereditary nature of the condition, there’s a 2 in 4 chance of her also being a carrier like both of her parents if she’s inherited one affected gene. You can read all about this condition on the rare disease day blog.
Another example of a hereditary condition is Marfan syndrome. Unlike cystinosis, Marfan syndrome is autosomal dominant. This means that only one affected gene is needed for a child to inherit the condition (in other words, only one parent needs to be diagnosed with it). According to the NHS, if one parent is diagnosed with Marfan syndrome, their children will have a 50% chance of inheriting the condition from them.
What does genetic mean?
Genetic conditions are characterised by a mutation or abnormality in an individual’s gene/s. As we inherit DNA from our parents, this is why many genetic conditions can also be hereditary, but this doesn’t mean that all genetic conditions are inherited from our parents, and Down’s syndrome is an example of this.
People with Down’s syndrome have an extra chromosome (usually having 3 copies of chromosome 21 rather than 2). In a vast majority of cases, this happens because of a one-off genetic change in either the sperm or the egg. Although the condition is determined before birth, it’s very rarely hereditary, as, in 99% of cases, neither of the parents of a child with Down’s syndrome have the condition themselves.
If my sibling has a condition, will I pass it on to my children?
This completely depends on the condition. If it’s an autosomal recessive condition like cystinosis, there’s a chance that you could be a carrier, and if you have a baby with another carrier, your child will have a 1 in 4 chance of developing the condition. However, with autosomal dominant conditions like Marfan syndrome, if you don’t have the condition yourself, it’s much less likely that you’ll pass the gene to your children.
If you’re worried about any genetic or hereditary condition that’s present within your family, we recommend making an appointment with your doctor, especially if you notice similar symptoms or you’re worried about any of your future children inheriting a disease.