Spinal muscular atrophy, lower extremity, dominant 2 (SMALED2) is a genetic disorder that causes muscle weakness and loss of muscle tissue (atrophy) in the legs (lower extremities). SMALED2 mainly affects the lower extremity muscles that are further away from (distal) and close to (proximal) the center of the body. However, some affected children may have muscle weakness that affects their arms (upper extremities). Symptoms usually present in early childhood and slowly get worse with time (progress). Children with this condition have trouble walking well (unsteady gait) and may also be delayed in walking.
SMALED2 is caused by a change (mutation) to the BICD2 gene. This gene provides instructions for the body to produce a protein that is important to the cells that send signals from the brain to the muscles (motor neurons). When the BICD2 gene has a mutation, the motor neurons do not work properly, leading to the symptoms of SMALED2. As its name suggests, this disease is inherited in an autosomal dominant way. This means a mutation in only one of the two copies of the BICD2 gene a person has is enough to cause the condition.
SMALED2 is usually considered in a child who has muscle weakness in the legs that presents in early childhood. Genetic testing of the BICD2 gene is used to confirm the diagnosis. Muscle weakness seen in SMALED2 is similar to the muscle weakness seen in other genetic conditions. A doctor may collect and examine a small muscle sample (biopsy) to look for clues for the diagnosis. There is no cure for SMALED2, but physical therapy can be helpful in strengthening the affected muscles. If your child has been diagnosed with SMALED2, talk with their doctor about all current treatment options. Support groups can provide additional information and connect you with other affected families.