A genetic disorder is a condition that’s caused by a change, called a mutation, in a gene. A disease-causing mutation generally interferes with the body’s production of a particular protein.

What is a gene?

Genes, made of the chemical known as DNA (deoxyribonucleic acid), are strings of chemicals that form a "rough draft" of the recipes (often called codes) for the thousands of proteins our bodies use to build cellular structures and carry out the functions of our cells. DNA is stored on strands called chromosomes, located mostly in the nucleus of each cell in the body.

How do genes lead to proteins?

A cell converts each gene (DNA sequence) into RNA in the nucleus. A fully processed copy of the gene's RNA moves out of the nucleus, where a protein is made from this RNA "recipe."

Proteins in nerve cells affect the way the cell receives and transmits signals, including those it sends to muscle fibers. Muscle fiber proteins affect muscle contraction and protect fibers from contraction-related damage.

The final copies of the protein recipes are actually carried in RNA (ribonucleic acid), a very close chemical cousin of DNA. The cell converts DNA to RNA in its nucleus. Each RNA recipe then leaves the cell's nucleus and becomes the instruction manual for the manufacturing of a protein outside the nucleus.

How do mutations in genes lead to problems in proteins?

A mutation in the DNA for any protein can become a mutation (error) in the RNA recipe and then an error in the protein made from those RNA instructions. Some mutations are worse than others for the cell.

Some mutations lead to production of a slightly abnormal protein, while others lead to a very abnormal protein or to the complete absence of a particular protein.

How do protein problems affect people?

The effects of a mutation in DNA in a person depend on many factors, among them exactly how the mutation affects the final protein (whether the protein is made at all and, if so, how close to normal it is), and how crucial that protein is in the body.

For example, some mutations in the gene for the protein dystrophin lead to relatively mild muscle weakness, while others lead to very severe weakness, depending on how much dystrophin is produced and how close it is to normal dystrophin.

The mutations leading to severe weakness ultimately threaten life because dystrophin is needed for cardiac and respiratory muscle functions. All this may seem like a lot of explanation, but it's the basis for how you and the professionals you consult can make decisions about any genetic disorder that may be in your family.

What do proteins do?

The functions of proteins include such things as sending or receiving signals to or from other cells, breaking down large molecules into smaller ones, combining smaller molecules to make larger ones, and producing energy for all cellular activities.

These activities ultimately result in functions like muscle contraction, digestion and metabolism of food, and regulation of blood pressure and temperature, as well as seeing, hearing, thinking and feeling.

What about the proteins in MDA-covered disorders?

The proteins involved in the genetic disorders that MDA covers are normally present in nerve cells or muscle cells. Proteins in nerve cells affect the way a nerve cell receives signals from other cells or transmits signals to other cells, including muscle cells.

Proteins in muscle cells affect the functions of the muscle cell, such as contraction (the action that moves muscles), the way in which the muscle cell receives signals from a nerve cell or the various mechanisms by which a muscle cell protects itself from the stresses of its own workload.

When genes for these nerve and muscle proteins are mutated, loss of or abnormalities in these proteins cause genetic neuromuscular disorders.