In this explainer episode, we’ve asked Ana Lisa Tavares, Clinical Lead for rare disease research at Genomics England, to explain what a rare condition is, in less than 10 minutes. You can also find a series of short videos explaining some of the common terms you might encounter about genomics on our YouTube channel If you’ve got any questions, or have any other topics you’d like us to explain, feel free to contact us on [email protected].   You can read the transcript below or download it here: https://files.genomicsengland.co.uk/documents/Podcast-transcripts/What-is-a-rare-condition.docx   Naimah: What is a rare condition? Today I’m joined by Ana Lisa Tavares, Clinical Lead for rare disease research at Genomics England, and she’s going to explain more. Ana Lisa: There are thousands of rare conditions. I hesitate to say a number as we’re learning all the time, so this keeps changing. There are estimated to be perhaps around 10,000 different rare conditions, as an order of magnitude. Many rare conditions start in childhood, 75% or three quarters affect children. A little over 10% affect adults, only adults, and some, around 20% can start in children or adults. Naimah: So, what makes a condition rare? Ana Lisa: A rare condition can be defined as affecting less than one in 2,000 people in the general population. This is a definition that’s used in Europe. Different parts of the world use slightly different numbers and definitions, so for example, the number of people with a rare condition living in that country, there isn’t one single universal definition. The important part I think is that this is a practical way to help shine a spotlight on rare conditions, which collectively affect a lot of people, and the particular challenges in making diagnoses and finding treatments for rare conditions. So together, it’s estimated 7% of people are affected by a rare disease in their lifetime, or one in 17, so that means that there are 3 and a half million people in the UK affected by a rare disease, and in the world, probably somewhere between 250 to 450 million people, so perhaps 350 million people, a really huge number. When you look into these numbers, there are rare conditions that are much more common than others. So, 80% of people with a rare condition have one of the 150 most commonly occurring rare conditions. Cystic fibrosis would be an example that many people will have heard of, and if you look at those numbers from a different angle, 85% of rare conditions affect less than one in a million people, so are very rare, and it’s important to bring together these different voices to solve some of the common challenges. Naimah: Can you explain to me how these differ from more common conditions? Ana Lisa: The simplest answer is that they are defined by the frequency, so how often they happen in the general population, and one reason for grouping together thousands of rare conditions is to highlight some of the particular challenges. This includes delays in getting a correct diagnosis that can often take years, an increased chance of a misdiagnosis before getting to an accurate diagnosis, and treatment challenges, as 95% of rare conditions don’t have a specific treatment. This is a very good question, and I would like to note that it’s also an artificial distinction to some extent. So, human conditions have a range of underlying causes that can be broadly grouped together, including genetic and environmental, such as a viral infection. However, it gets complicated, for example, a proportion of common conditions that may have many different causes will have a genetic component, so for example causing an early onset familial form of a condition, such as diabetes. And in fact, genetic causes may give or can give the clue or the key that’s necessary to develop a new drug therapy that can then help many people with the condition, so those that may have a rare genetic cause and those that have a more