Health Problem: Spinal muscular atrophy (SMA) is a recessive genetic disorder characterized by progressive proximal muscle weakness and atrophy. SMA is predominantly caused by deletions or mutations of survival motor neuron (SMN) SMN-1, which leads to degeneration of alpha motor neurons of the spinal cord anterior horn cells. This affects the proximal muscles, such as those of the legs, arms, and neck. There is no cure for SMA. Treatment consists of managing symptoms.
Technology Description: Since patients with SMA have a deleted or mutated SMN-1 gene, they produce no SMN-1 protein. The very low level of full-length SMN-2 protein is insufficient to sustain motor neurons and they degenerate. Nusinersen (Spinraza; Biogen) is an SMN-2 antisense oligonucleotide that modifies transcription of the SMN-2 gene to create more copies of full-length SMN protein.
Controversy: Nusinersen was recently approved by the Food and Drug Administration based on 2, small, randomized, sham-controlled trials that were terminated early due to the favorable effects of nusinersen on motor function and event-free survival. Because of the priority review of nusinersen, an orphan drug, the efficacy and safety of nusinersen and the ideal patient population for nusinersen treatment have not been fully evaluated.
Key Questions:
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Is nusinersen effective in treating SMA in infants and children?
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How does nusinersen compare with other treatments for SMA?
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Is treatment with nusinersen safe?
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Have definitive patient selection criteria been identified for nusinersen?
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