Drug treatment for spinal muscular atrophy types II and III

Spinal muscular atrophy (SMA) is a neuromuscular disorder that results in progressive muscle weakness with onset in childhood and adolescence. There are three main types of SMA. Drug treatment for SMA type I is discussed in a separate Cochrane review. This review is of drug treatment for SMA types II and III. Both of these reviews were first published in 2009 and are now updated. The age of onset of SMA type II is between six and 18 months. Children with SMA type II will never be able to walk without support; they survive beyond two years and may live into adolescence or longer. The age of onset of SMA III, also known as Kugelberg-Welander disease, is after 18 months. Children with SMA type III develop the ability to walk at some time and their life expectancy is normal. From six randomised controlled trials, there is no evidence for a significant effect on the disease course when patients with SMA types II and III are treated with creatine (55 participants), phenylbutyrate (107 participants), gabapentin (84 participants), thyrotropin releasing hormone (9 participants), hydroxyurea (57 participants) or combination therapy with valproate and acetyl-L-carnitine (61 participants). The risk of bias of the included trials was systematically analysed and none of the studies were completely free of bias. Thus, there is still no known efficacious drug treatment for SMA types II and III.

Authors' conclusions: 

There is no proven efficacious drug treatment for SMA types II and III.

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Background: 

Spinal muscular atrophy (SMA) is caused by degeneration of anterior horn cells, which leads to progressive muscle weakness. Children with SMA type II do not develop the ability to walk without support and have a shortened life expectancy, whereas children with SMA type III develop the ability to walk and have a normal life expectancy. There are no known efficacious drug treatments that influence the disease course of SMA. This is an update of a review first published in 2009.

Objectives: 

To evaluate whether drug treatment is able to slow or arrest the disease progression of SMA types II and III and to assess if such therapy can be given safely. Drug treatment for SMA type I is the topic of a separate updated Cochrane review.

Search strategy: 

We searched the Cochrane Neuromuscular Disease Group Specialized Register (8 March 2011), Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 1), MEDLINE (January 1991 to February 2011), EMBASE (January 1991 to February 2011) and ISI Web of Knowledge (January 1991 to March 8 2011). We also searched clinicaltrials.gov to identify as yet unpublished trials (8 March 2011).

Selection criteria: 

We sought all randomised or quasi-randomised trials that examined the efficacy of drug treatment for SMA types II and III. Participants had to fulfil the clinical criteria and have a deletion or mutation of the survival motor neuron 1 (SMN1) gene (5q11.2-13.2) that was confirmed by genetic analysis.

The primary outcome measure was to be change in disability score within one year after the onset of treatment. Secondary outcome measures within one year after the onset of treatment were to be change in muscle strength, ability to stand or walk, change in quality of life, time from the start of treatment until death or full time ventilation and adverse events attributable to treatment during the trial period.

Data collection and analysis: 

Two authors independently reviewed and extracted data from all potentially relevant trials. Pooled relative risks and pooled standardised mean differences were to be calculated to assess treatment efficacy. Risk of bias was systematically analysed.

Main results: 

Six randomised placebo-controlled trials on treatment for SMA types II and III were found and included in the review: the four in the original review and two trials added in this update. The treatments were creatine (55 participants), phenylbutyrate (107 participants), gabapentin (84 participants), thyrotropin releasing hormone (9 participants), hydroxyurea (57 participants), and combination therapy with valproate and acetyl-L-carnitine (61 participants). None of these studies were completely free of bias. All studies had adequate blinding, sequence generation and reports of primary outcomes.

None of the included trials showed any statistically significant effects on the outcome measures in participants with SMA types II and III. One participant died due to suffocation in the hydroxyurea trial and one participant died in the creatine trial. No participants in any of the other four trials died or reached the state of full time ventilation. Serious side effects were infrequent.

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