DMD (Duchenne Muscular Dystrophy) and SMA (Spinal Muscular Atrophy) are both genetic disorders affecting muscles, but they differ in their cause, inheritance pattern, and the specific muscles primarily affected.
Duchenne Muscular Dystrophy (DMD)
Duchenne Muscular Dystrophy (DMD) is an X-linked recessive genetic disorder primarily affecting males. It is caused by mutations in the DMD gene, which provides instructions for making dystrophin. Dystrophin is a protein that is crucial for maintaining the structure and function of muscle fibers.
- Cause: Mutations (often deletions, but also duplications or smaller variants) in the DMD gene located on the X chromosome. These mutations prevent the body from producing functional dystrophin.
- Inheritance: X-linked recessive. This means males (who have one X and one Y chromosome) are more likely to be affected, as they only have one copy of the X chromosome. Females (who have two X chromosomes) are usually carriers, but can be affected in rare cases.
- Affected Muscles: Primarily affects skeletal muscles (muscles used for movement) and the heart (cardiac muscle).
- Symptoms: Muscle weakness that begins in early childhood (typically between ages 2 and 5), difficulty walking, frequent falls, and eventually progressive loss of muscle function. Cardiomyopathy (weakening of the heart muscle) is a common and life-threatening complication.
- Diagnosis: Genetic testing to identify mutations in the DMD gene, muscle biopsy, and elevated levels of creatine kinase (CK) in the blood.
Spinal Muscular Atrophy (SMA)
Spinal Muscular Atrophy (SMA) is an autosomal recessive genetic disorder that affects motor neurons, which are nerve cells in the spinal cord that control muscle movement.
- Cause: Most commonly caused by homozygous deletions or mutations in the SMN1 gene (Survival Motor Neuron 1). This gene provides instructions for making a protein called SMN, which is essential for the survival and function of motor neurons.
- Inheritance: Autosomal recessive. This means that both parents must be carriers of the mutated gene for a child to be affected.
- Affected Muscles: Primarily affects motor neurons in the spinal cord, leading to muscle weakness and atrophy (wasting away).
- Symptoms: Muscle weakness, hypotonia (floppy muscle tone), difficulty breathing and swallowing, and eventually paralysis. The severity of SMA varies depending on the type, with some forms being fatal in infancy.
- Diagnosis: Genetic testing to identify mutations or deletions in the SMN1 gene.
Summary Table
| Feature | Duchenne Muscular Dystrophy (DMD) | Spinal Muscular Atrophy (SMA) |
|---|---|---|
| Gene Affected | DMD | SMN1 |
| Inheritance Pattern | X-linked recessive | Autosomal recessive |
| Primary Tissue Affected | Muscle | Motor neurons |
| Protein Affected | Dystrophin | SMN (Survival Motor Neuron) |
In essence, DMD is a muscle disease caused by a lack of dystrophin, while SMA is a motor neuron disease caused by a deficiency of the SMN protein, both leading to muscle weakness and functional impairment.
