Type I Spinal Muscular Atrophy (SMA), also known as Werdnig-Hoffmann Disease, is a rare genetic disorder characterized by the degeneration and loss of specialized nerve cells called motor neurons in the spinal cord and brainstem. This disorder primarily affects the lower motor neurons responsible for controlling voluntary muscle movements, leading to progressive muscle weakness, muscle atrophy (wasting), and a diminished ability to move.
Type I SMA is considered the most severe subtype and typically manifests within the first few months of life, often before six months of age. Infants with Type I SMA typically present with weak muscle tone (hypotonia) and impaired motor skills, such as difficulties in holding up the head, sitting, or rolling over. As the condition progresses, the muscle weakness worsens, affecting the ability to swallow, cough, and breathe independently.
This form of SMA is caused by mutations in the survival motor neuron 1 gene (SMN1) and is inherited in an autosomal recessive manner. The absence or dysfunction of the SMN protein, which is necessary for the survival and function of motor neurons, leads to their progressive degeneration.
Type I SMA has a high morbidity rate and can be life-threatening due to the weakened respiratory muscles, making respiratory complications a primary concern. However, recent advancements in gene therapy and supportive care have shown promising results in improving both survival and quality of life for individuals with Type I SMA.
