Understanding Spinal Muscular Atrophy (SMA)

Spinal muscular atrophy (SMA) is an inherited disorder that impacts the nervous system, specifically affecting the nerves responsible for voluntary muscle movements. When the nerve signals fail to reach the muscles, they weaken and waste away, resulting in muscle atrophy. The severity of impairment varies with age at onset; infants often experience the most significant weakness, while older individuals may retain more motor function.

SMA primarily results from mutations in the SMN1 gene, leading to insufficient production of the survival motor neuron (SMN) protein necessary for healthy motor neuron operation. This condition mainly targets proximal muscles such as shoulders, hips, thighs, and upper back, causing issues like spinal curvature, swallowing difficulties, and breathing problems. Importantly, SMA does not affect sensory or cognitive functions.

SMA classification includes types 1 through 4, corresponding to age and motor abilities, with type 1 affecting infants and types 2-4 affecting older children and adults, respectively. The condition is inherited when both copies of the mutated SMN1 gene are present, often with parents being carriers without symptoms. Rare cases involve new mutations occurring during egg or sperm formation or early embryonic development.