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One of the most abundant and complex elements that contributes to who we are is our genes.

It is estimated that humans have between 20,000 to 25,000 of them.

To understand what causes Duchenne muscular dystrophy, a rare genetic disorder, it’s essential to understand what genes are and how changes or mutations to their makeup can cause a condition like Duchenne.

What is a gene?

DNA is the information that our body uses to build all the different types of cells and tells them how to function. DNA is made up of thousands of regions, which we call genes, wound up tightly into chromosomes. Each gene contains information for a particular role or function of the cell or body.

Image depicting breakdown of DNA, chromosomes, genes, cells and nucleus

What is a chromosome?

Chromosomes are made up of tightly wound ribbons (or coils) of DNA and as many as tens of thousands of genes. Most people have 46 chromosomes or 23 pairs of chromosomes in each cell, one inherited from mom and the other from dad. When all lined up, the first 22 pairs look like different sized pairs of socks as shown below. The 23rd pair are the sex chromosomes, and they are the only pair that do not match up because they differ between males and females. Males have one X and one Y chromosome, while females have two copies of the X chromosome.

Image depicting chromosomes

Since DNA is so important, it is kept in a protected region of the cell called the nucleus.

Image depicting cell, nucleus, and chromosome

Here, the DNA is kept away from substances and environments that could cause damage to the instructions it is intended to create. While cells normally work to prevent DNA from being changed, sometimes a mistake in the DNA can result from random errors, and this is called a mutation.

What is a genetic mutation?

When an error occurs, which we call a mutation, it might only be a minor change and there may not be any negative consequences. But in some cases, the mutation has a very negative effect, resulting in the cells or organs being unable to function the way they are supposed to. This is called a disease-causing (pathogenic) change. In Duchenne muscular dystrophy (DMD), there is a pathogenic change in the DMD gene (the gene responsible for making the protein dystrophin). It is a mutation in the DNA of this gene that is the root cause of all the symptoms we see in people living with Duchenne muscular dystrophy.

Click the button to learn more about the types of genetic mutations.

Most genes in the body, including the DMD gene, contain the instructions for making a protein. Proteins do most of the work in the cell. For example, they are responsible for building and growth, sending messages, causing chemical reactions, providing structure and a whole host of other functions. When a protein is not being made properly or is not made at all, there can be many negative effects on cells and the tissues they make up. In Duchenne, the mutation in the DMD gene prevents the production of the dystrophin protein.

Image depicting the breakdown of proteins in the muscle cell to help identify dystrophin

Click the button below to learn more about the role of dystrophin.

How is Duchenne passed on or inherited?

The dystrophin gene that causes Duchenne muscular dystrophy is found on the X chromosome and is the reason why Duchenne primarily effects males while females are called carriers. When a change alters the X chromosome, females have a second copy to make up for it. However, they can pass on their altered X chromosome to their children. However, Duchenne is not always inherited from a carrier mother. Approximately 70% of cases are caused from an inherited mutation from the mother while 30% of cases are a result of what is called a de novo mutation or spontaneous mutation.

Click the button below to learn more about what it means to be a carrier.