SNP Shot: Genomic Insights

Spinal muscular atrophy with lower extremity predominance (SMA-LED) is a condition marked by muscle weakness and atrophy primarily affecting the lower limbs. The quadriceps, located in the thighs, are typically the most affected muscles. The "D" in SMA-LED signifies its dominant inheritance pattern. This condition arises from the loss of motor neurons, which control muscle movement, leading to muscle atrophy in the legs. Individuals with SMA-LED often exhibit an unsteady, waddling gait and tend to walk on the balls of their feet. Activities such as rising from a seated position and climbing stairs can be challenging. Upper limb muscle weakness can also occur in some cases.

Joint contractures, or deformities, can develop in the hips, knees, feet, and ankles of individuals with SMA-LED. In more severe instances, these contractures may be present at birth and can hinder the ability to walk. Some individuals also experience joint rigidity, known as arthrogryposis, in their shoulders, elbows, and hands.

While muscle problems typically manifest during infancy or early childhood in most individuals with SMA-LED, approximately 25% of affected individuals do not experience muscle weakness until adulthood. Generally, the muscle weakness and associated health issues do not progressively worsen over time.

Inheritance:

SMA-LED follows an autosomal dominant inheritance pattern. This means that having only one copy of the mutated gene in each cell is enough to cause the disorder. The mutation can be inherited from one affected parent. However, in some cases, the mutation is new, arising spontaneously in the affected individual, even when there is no family history of SMA-LED.