The science behind EB research

EB is a spectrum of diseases with symptoms that can be different from one person to the next. 

Different types of EB can be caused by changes in the genes for skin proteins like keratin and collagen. Within each type, symptoms can be more or less extreme and there are quite a few named sub-types of EB where a slightly different set of symptoms have been described by a researcher. In 2020 a DEBRA-funded expert consensus report was published that reclassified all genetic EB into one of four types:

This animation explains a bit about EB at the molecular level: 

The Genetic Alliance UK website provides information about genetic conditions in general.

Cells are living things that can be independent like bacterial cells, yeast cells or an amoeba or they can cluster together and take on different jobs to make a multi-cellular creature like a human, chicken, mushroom or tree.  

Within a multi-cellular creature, different cells exist that look very different (if you’ve got a good microscope) and do very different things. They’re about 1/100 to 1/10 of a millimetre in size so you can’t see individual cells with the naked eye. Skin cells look different to blood cells, red blood cells look different to white blood cells and there are different types of white blood cells that do different jobs as part of our immune system. Cells that look different through a microscope or that do different things are given different names by researchers. For example: macrophages are cells involved in inflammation and wound healing – they start off as monocytes, happily whooshing around in our blood, but when skin is wounded, they stick to the damaged area and become macrophages that can help fix the damage. Fibrocytes are skin cells that are involved in scarring (fibrosis) and making collagen. Keratinocytes are skin cells that make lots of keratin, a skin protein that doesn’t work properly for many people with epidermolysis bullosa simplex (EBS). Researchers call skin cells ‘epithelial cells’. These are the cells that are involved in making our skin and the layers that cover our internal organs and the insides of our breathing pipe (windpipe or trachea) and food pipe (oesophagus).

Some potential treatments for EB involve growing skin cells in a laboratory.

Researchers sometimes put new treatments directly onto cells grown in a laboratory to see how (or if) they might work before using them on an actual living creature. This is easier, cheaper, safer and reduces the use of animals in research. However, the results might not be quite as useful for patients because cells in a dish are often a little bit different to the ones inside us so may behave differently. It’s also easier to apply a treatment directly to cells in a dish than to get a medicine to them when they are part of a living human body so researchers must consider how their medicine will get to the right cells as part of developing a treatment that works.

Some potential EB treatments are based on stem cells. These are a specific type of cell that can transform itself into other types of cell. Treatments can use autologous stem cells which come from a person’s own body or allogeneic stem cells which come from somebody else. Stem cells are often taken from bone marrow but can come from other parts of the body.

Image credit: Stem cell differentiation, by Haileyfournier. Licensed under the Creative Commons Attribution-Share Alike 4.0 International license.

We think of protein as being a food group – meat and pulses – but this stuff called ‘protein’ is made up of lots of very different individual ‘molecules’. A molecule is what you get when lots of atoms – of carbon, hydrogen, oxygen, nitrogen and other elements – are stuck together. You can make models of different molecules using blobs of playdoh and straws or computer animation programs. Protein molecules are far too small to see with a microscope that would show us cells easily. They’re what cells are made out of; they make up the stuff that cells are glued together with and they are how cells communicate with each other. ‘Enzymes’ are a type of proteins that help chemical reactions to happen and are important in our bodies for things like digesting food. The specific 3D shape of each protein molecule is very important for how they stick to each other and carry out their specific jobs inside our bodies. Our skin is made from lots of different cells and proteins all sticking to each other. 

Protein molecules are long chains of amino acids (smaller molecules). When we eat protein, our digestive system breaks that delicious steak up into individual amino acids and takes them into our blood. Our bodies can then put the amino acids back together again in a different order to make the proteins we need – turning cow protein into human protein! 

There are 20 common amino acids, each slightly different, a bit like having 20 different types of Lego blocks.

When they are stuck together following specific instructions, we end up with a protein that can contain hundreds or thousands of amino acids (a big molecule). This might look like an impressive Lego sculpture… or a small part of one. Creating a protein is like following the Lego instructions. If one step is missing, or you accidentally turn over two pages at a time, the whole, beautiful protein at the end can be completely broken. Quite often, the final, working protein, is made up of many different smaller proteins, each one a separate chain of amino acids from a separate instruction booklet, all carefully linked together. When we talk about proteins like keratin and collagen, we are talking about huge protein structures that are put together from lots of different, smaller proteins, each one with its own instruction booklet (gene) and specific order of amino acids. These chains of amino acids twist around each other and stick together in specific ways to make lots of different versions with slightly different jobs within our bodies. Keratin and collagen are actually groups of proteins. There are lots of different types of keratin and lots of different types of collagen but they are both proteins that form long fibres by twisting chains of amino acids around each other. 

Image credits: 

Amino Acid Structure, by Techguy78. Licensed under the Creative Commons Attribution-Share Alike 4.0 International license.
Lego blocks, by Ypiyush22. Licensed under the Creative Commons Attribution-Share Alike 4.0 International license.
Collagentriplehelix-es, by Vossman, Modificado por Alejandro Porto. Licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

DNA is another type of molecule (like protein) made out of little molecules joined together. 

A chromosome is a DNA molecule that is so long it can be rolled and folded up so that it *is* big enough to see inside a cell’s nucleus with a microscope. We have 23 chromosomes that come in pairs: one copy of each chromosome from each of our parents.

Where proteins are long chains made with 20 different subunits (amino acids), DNA is a long chain made up of only four different subunits called ‘bases’ and named A, C, G and T. Every three letters (triplet) on a DNA chain, corresponds to one of the 20 amino acids or says STOP or START, so the DNA ‘code’ can be ‘read’ as a list of amino acids to join together in order to make a protein. This process happens inside our cells all the time with many different sorts of proteins being made from the DNA instructions on our chromosomes. 

Each chromosome is a single DNA molecule millions of bases long and a lot of the As, Cs, Gs and Ts don’t seem to do much. But the stretches that are instructions for making proteins are called genes. Each of our chromosome carries genes for hundreds of proteins. It’s all so complicated that it’s not surprising it sometimes goes wrong. If a single DNA letter is missing (deletion), the rest of the triplets will no longer code for the right amino acids and the protein that is made will not look at all like it should. 

Sometimes a single DNA letter is swapped giving us an A instead of a C, for example. This might only affect one Lego brick (or amino acid) in the final protein and might not make much difference…. Or it could mean that the protein can’t stick to the other proteins it needs to in order to work properly and cause symptoms in a family with that DNA change.

Image credits:

DNA-molecule3, by ynse from Poland. Licensed under the Creative Commons Attribution-Share Alike 2.0 Generic license.
Human karyotype (263 17) Karyotype Human, 45,XY t13-14, by Doc. RNDr. Josef Reischig, CSc. Licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
Effect of a mutation (13080960754), by Genomics Education Programme. Licensed under the Creative Commons Attribution 2.0 Generic license.

Genes are generally made up of exon sequences (where the As, Cs, Gs and Ts code for protein as described above) and intron sequences (that don’t spell out a protein).

The collagen gene involved with DEB (COL7A1) has over a hundred exons with introns in between. For the normal protein to be made, the genetic ‘recipe’ is read by jumping from exon to exon and ignoring the introns. If one of the exons contains a change that causes the whole protein to be broken, a type of therapy called ‘exon skipping’ might be used to make a protein that leaves out that exon along with the introns. The resulting protein is a bit shorter, but still works. This therapy has the potential to help people with EB and has been used in a different genetic condition called Duchenne Muscular Dystrophy, explained in this animation: 

We may think of our immune system as being just the antibodies and white blood cells that protect us from germs but there’s a lot more to it than that. Many researchers focus on small parts of the immune system that are particularly relevant to EB. This can be specific cells that are involved in wound healing or inflammation or specific proteins that tell different cells what to do when skin damage occurs. Researchers might first need to carefully look at what is going on before they can even think of ways to help with symptoms.

White blood cells (lots of different types with lots of different names!) are outnumbered in our blood by the red blood cells that have a different job of carrying oxygen and carbon dioxide around our bodies. As well as making antibodies and killing germs, white blood cells are involved in an important process in EB called inflammation.

Inflammation is what happens when our skin is damaged. We see swelling and redness and feel pain, warmth and itching. White blood cells are carried to the wound and stick there where some will become macrophages and help to protect the damaged area. Inflammation shouldn’t go on for longer than it needs to and should reduce over a day or two and lead to wound healing. In EB, inflammation can be ‘chronic’ rather than ‘acute’ meaning that it carries on after it has stopped being useful and may become a cause of symptoms rather than helping with healing.

How does the immune system work?

After our skin has been damaged and become inflamed, it can sometimes heal so well that it looks like there has never been an injury. But a more severe wound is repaired using a process called fibrosis that produces a scar. This process involves cells called fibrocytes and proteins like collagen to glue our skin back together. In epidermolysis bullosa, skin proteins like collagen might not be working properly so the process of wound healing might not happen in the way it is expected to. Understanding how wound healing and scarring are supposed to happen can help researchers to find out which parts of the process are affected in EB and find targets for treatments. 

Image credit: 417 Tissue Repair, by OpenStax College, Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013. Licensed under the Creative Commons Attribution 3.0 Unported license.

Cancer is what happens when our cells don’t die when they should but continue to divide and multiply to produce a lump or bump where there shouldn’t be one. Cancers don’t grow new functioning organs: skin cancer doesn’t grow you a new skin, lung cancer doesn’t grow you a new lung – because it is just one type of cell in a beautiful, complex, multicellular organ, that is multiplying when it shouldn’t. These lumps of cancer cells can get in the way of how our bodies are working by blocking tubes, squashing nerves and doing damage to our organs. If a cancer cell breaks away from the first cancer, it can spread around the body, stick somewhere else and grow a secondary cancer. The cells of our immune system can kill off some cancer cells but they have to be careful not to kill our own healthy cells so this is a tricky process. Understanding our immune system may help researchers to target cancer cells.

Our cells usually kill themselves when they are no longer needed but, every now and then, one doesn’t and becomes cancerous. This is more likely to happen if the DNA inside that individual cell has been damaged in some way, by UV light (sunburn) or by an inherited change to a gene that is involved in telling cells when to stay alive and when to kill themselves. Researchers try to understand the genes and proteins involved in cell suicide (apoptosis) because they may be targets for cancer therapies. 

For cancer cells to keep growing and dividing they need our blood to bring them more oxygen and nutrients in a process called inflammation. Inflammation is important for our bodies to react to a wound but long-term inflammation can support the development of cancer. Researchers try to understand how inflammation starts and stops and why it might not work properly to come up with new treatments for people with EB.

People with recessive dystrophic epidermolysis bullosa (RDEB) have an increased likelihood of developing a type of skin cancer called squamous cell carcinoma (SCC). This is a non-melanoma skin cancer with a lower likelihood of spreading to other parts of the body than melanoma (5% or 1 in 20). It starts in the top layer of skin (epidermis) where the multiplying cancer cells form a firm lump that may feel tender and bleed easily. 

Image credit: Squamous Cell Carcinoma, by BruceBlaus. Licensed under the Creative Commons Attribution-Share Alike 4.0 International license.

Our skin has an outer layer, called the epidermis, and a lower, thicker layer called the dermis. Between the epidermis and the dermis there’s a thin layer called the basement membrane that is made from proteins like collagen and laminin and glues the epidermis and dermis together. When the proteins of the basement membrane don’t work properly, the two layers are not held together strongly and the skin is easily damaged causing symptoms of EB.

The outermost layer of our skin (epidermis) is made out of keratin protein and the cells, called keratinocytes, that make keratin. New keratinocytes are made when cells near the basement membrane divide and they push the older keratinocytes up towards the surface of the skin. These cells make more and more keratin until they are full of it and die. Normal skin has a layer of dead cells and keratin as its surface and this flakes off to be replaced by more growing up from beneath. The protein keratin is made from lots of protein subunits, joined and twisted together in long chains, each one encoded by a different gene. Changes to genes involved in making keratin can cause epidermolysis bullosa simplex.

Beneath the epidermis is the dermis. This is made mostly out of collagen protein and contains cells like macrophages that protect against germs and fibroblasts that produce collagen. Like keratin, collagen protein is made from lots of collagen subunits, each encoded by a different gene. Changes to the COL7A1 gene cause dystrophic epidermolysis bullosa.

Other proteins that can be broken in EB include laminin which is used to make the basement membrane between the epidermis and the dermis as well as forming the ‘glue’ in between skin cells (the extracellular matrix) and integrin which fixes skin cells into position in the extracellular matrix. 

Anatomy and physiology of the skin

Image credit: 3D medical animation skin layer, by https://www.scientificanimations.com/. Licensed under the Creative Commons Attribution-Share Alike 4.0 International license.

EB is a genetic condition which means the symptoms are caused by changes to our DNA, sometimes called ‘mutations’. We can inherit these genetic changes from one or both parents or they can happen for the first time in the egg or sperm that made us, called a ‘spontaneous’ or ‘de novo’ mutation. 

Genetic conditions are not catching, they are ‘congenital’ which means they are something a person is born with. They are nobody’s fault and not due to anything anyone did or didn’t do – they are just down to chance. Copying our DNA each time a new cell is made is complicated and our bodies simply don’t get it right every single time. There will be DNA changes (mutations) in every individual person that don’t do any harm at all but sometimes they change the DNA instructions for making proteins in our skin and we get symptoms of EB. The changed DNA exists in all our cells including those that make our own eggs and sperm and can be passed on to our children. But different types of EB are inherited in different ways and the symptoms will not always be passed on.

Image credit: Egg and Sperm, by Christinelmiller. Licensed under the Creative Commons CC0 1.0 Universal Public Domain Dedication.

Sometimes only one copy of a gene is changed and may either make no protein at all or a broken protein that doesn’t work properly. If we can make enough fully working protein from the unchanged copy the person may have no symptoms and be described as a ‘carrier’. The genetic change might be described as ‘recessive’. 

When two parents are both ‘carriers’, their children have a 50% chance (1 in 2 – like flipping a coin and getting heads) of inheriting a broken copy from either parent which will make the child a carrier too. They have a 25% chance (1 in 4 – like flipping two coins at the same time and getting heads on both) of inheriting a broken copy from both parents. This will cause symptoms because the child won’t have any of the working protein and they will be born with EB. There’s also the same 25% chance (1 in 4) that a child will inherit the perfectly working copies from both mum and dad and be totally unaffected, not even a carrier. They will not pass on EB to their own children. 

Recessive genetic diseases have unaffected family members who are carriers of the broken gene without having symptoms themselves. 

People with symptoms of recessive EB have two broken copies of the affected gene so will pass on a broken one to all their children. If the other parent has two working copies, all the children will be carriers. If the other parent is a carrier there is a 50:50 (like tossing a coin) chance of the children being affected as they may either inherit the broken copy or the working copy.

Image credit: Autorecessive_en_01, by Kuebi (Armin Kübelbeck). Licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

Sometimes the broken protein made from a changed gene (mutation) gets in the way of the working protein from the other copy or having a reduced amount of the working protein is enough to cause symptoms. In these cases, people will have symptoms even if they have inherited a fully working gene from one of their parents. The genetic disease might be described as ‘dominant’ because everyone who has the changed gene will have symptoms. This means that an affected parent may pass on either their broken version of the gene or the perfectly working version. Their children may have a 50:50 (like tossing a coin) chance of inheriting the broken gene and the symptoms.  

Sometimes it’s not quite so simple and a ‘carrier’ may have very mild or slightly different symptoms while someone with two broken copies of a gene may have a very severe disease.

Image credit: Autodominant_en_01, by Kuebi (Armin Kübelbeck). Licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

Gene therapy is a way of treating genetic conditions that tries to correct the underlying genetic change that is responsible for symptoms rather than treating the symptoms themselves.

Gene therapy uses natural processes from viruses and bacteria to create working genes and deliver them into our cells. This can either be by taking a person’s cells into the laboratory to make genetic corrections then returning them (called ex vivo) or by treating a person with a method that allows the working gene to be delivered to the cells in their body that need it (called in vivo).

Some treatments are taken as tablets. This is called an ‘oral’ route of delivery or ‘by mouth’ and means the medicine gets swallowed into our stomachs and starts being digested before it gets into our blood. Once it’s in our blood it is circulated around our whole body and can affect every organ. This is called a ‘systemic’ treatment and is different to a ‘local’ or ‘topical’ treatment which might use a cream, spray, gel or dressing to put medication only onto one part of the body. 

This video explains how systemic medicines can work inside our bodies:

Some systemic treatments can be ‘targeted’ so that, although they are in our blood, they only act on injured areas. 

Some systemic treatments might be put directly into our blood as an ‘intra-venous (IV) transfusion’. This means they don’t need to pass through our stomach first and can start working more quickly after they are given. If a medicine might be damaged by going into our stomachs or can’t get from our guts into our bloodstream it can’t be taken as tablets and might have to be transfused.

Creams, gels and sprays can apply a treatment directly to an area of wounded skin and are called topical or local treatments. They don’t really pass into our bloodstream so don’t affect any other parts of the body. 

Topical treatments are made up of an inactive substance called the ‘base’ and an ‘active ingredient’ that has biological effects on the body. The base might be a greasy cream, a blobby gel or watery liquid for dropping or spraying and a small amount of an active ingredient may be mixed into the base. Some creams are beneficial on their own by providing a protective barrier or helping to keep skin flexible while it heals but a medicated cream contains an active ingredient at a specific dose and may need to be used a certain number of times per day to be effective and not more than this. Researchers need to find out how much of their active ingredient to mix in with the base, what sort of base to use, how runny or sticky it needs to be, whether it needs to be shaken before use to mix the active ingredient evenly through it or stored in the fridge or freezer to keep the active ingredient working. They may look at ways to reduce stinging or take away an unpleasant taste or smell.

Some researchers study the methods of drug delivery rather than the actual drugs themselves. To make the best medicines, the two groups of experts can work together.