Duchenne muscular dystrophy is a genetic disorder that primarily affects muscle strength and function. It is caused by changes in the DMD gene, which provides instructions for producing dystrophin, a protein that helps protect muscle fibers from damage. Because the DMD gene is located on the X chromosome.
Duchenne muscular dystrophy (DMD) is an inherited neuromuscular disorder characterized by progressive muscle weakness. It usually becomes noticeable during early childhood, when children may experience difficulty running, climbing stairs, jumping, or getting up from the floor. The condition results from alterations in the DMD gene, which is responsible for producing dystrophin. Without sufficient functional dystrophin, muscle fibers become more vulnerable to damage during normal movement and gradually deteriorate.
The primary cause of Duchenne muscular dystrophy is a disease-causing variant in the DMD gene. This gene is located on the X chromosome and is one of the largest known human genes. Different types of genetic changes can interfere with dystrophin production or result in a shortened or nonfunctional dystrophin protein.
Common genetic changes associated with DMD include:
Deletions: Sections of the DMD gene are missing. These account for a substantial proportion of disease-causing variants.
Duplications: Extra copies of sections of the gene are present and can interfere with normal dystrophin production.
Small genetic changes: Smaller alterations, such as changes in individual DNA building blocks, can also disrupt the gene's instructions.
New mutations: Some affected children inherit the genetic change from their mother, while others have a new genetic change that was not previously present in the family.
The absence or severe reduction of functional dystrophin makes muscle cells less stable. Repeated muscle activity can therefore contribute to progressive muscle fiber injury and replacement of damaged tissue with fat and connective tissue.
Duchenne muscular dystrophy follows an X-linked inheritance pattern. Males typically have one X chromosome and one Y chromosome. If their single X chromosome contains a disease-causing DMD variant, they generally develop the condition because they do not have another X chromosome carrying a functional copy of the gene.
Females generally have two X chromosomes. A female who carries a disease-causing DMD variant on one X chromosome is often described as a carrier. Many carriers have no major symptoms, although some can develop muscle-related or heart-related complications.
Important inheritance considerations include:
A carrier mother may pass the altered DMD gene to her children.
Sons who inherit the altered X chromosome are generally affected.
Daughters who inherit the altered X chromosome may become carriers.
A father with DMD does not pass his X chromosome to his sons, so he does not transmit the DMD variant directly to them.
A father with the disease passes his X chromosome to all of his daughters, meaning they may inherit the altered gene.
Genetic testing can identify disease-causing changes in the DMD gene and can help confirm a diagnosis. Testing may also be considered for family members when appropriate. Genetic counseling can provide information about inheritance patterns, reproductive considerations, and the potential implications for relatives.
Understanding the genetic basis of DMD is important because the condition can occur even when there is no known previous family history. A new genetic change or previously unrecognized carrier status may explain why a child is affected.
Overall, Duchenne muscular dystrophy is primarily caused by genetic changes affecting the DMD gene and dystrophin production. Its X-linked inheritance pattern explains why it predominantly affects males while females may carry the altered gene. Genetic evaluation and counseling can help families understand the diagnosis and possible inheritance patterns. Continued research into the DMD gene and dystrophin biology also contributes to the development and evaluation of different approaches to managing the condition.