Spinal muscular atrophy (SMA) is now among the disorders officially included in the Recommended Uniform Screening Panel (), which is used by state public health departments to screen newborns for genetic disorders.
Secretary of the Department of Health and Human Services Alex M. Azar II formally added SMA to the panel July 2 on the recommendation of the Advisory Committee on Heritable Disorders in Newborns and Children.
“Adding SMA to the list will help ensure that babies born with SMA are identified, so that they have the opportunity to benefit from early treatment and intervention,” according to a statement from the Muscular Dystrophy Association about the decision. “This testing can also provide families with a genetic diagnosis – information that often is required to determine whether their child is eligible to participate in clinical trials.”
Adding SMA to the RUSP does not mean states must screen newborns for the disorder. Each state’s public health apparatus decides independently whether to accept the recommendation and which disorders on the RUSP to screen for. Most states screen for most disorders on the RUSP. Evidence compiled by the advisory committee suggested wide variation in resources, infrastructure, funding, and time to implementation among states.
An estimated 1 in 11,000 newborns have SMA, a disorder caused by mutations in the survival motor neuron 1 (SMN1) gene. SMA affects motor neurons in the brain stem and spinal cord leading to motor weakness and atrophy. The only treatment for SMA had been palliative care until the Food and Drug Administration approved nusinersen () for the disorder in December 2016, although the drug’s approval has raised some ethical questions.1-3
After reviewing the evidence at their February 8, 2018, the advisory committee recommended the addition of spinal muscular atrophy screening to the RUSP in a March 8, 2018, letter from committee chair Joseph A. Bocchini Jr., MD, who is a professor and the chairman of the department of pediatrics at Louisiana State University Health in Shreveport.
Secretary Azar accepted the recommendation based on the evidence the committee provided; he also requested a follow-up report within 2 years “describing the status of implementing newborn screening for SMA and clinical outcomes of early treatment, including any potential harms, for infants diagnosed with SMA.”
The advisory committee makes its recommendations to the HHS on which heritable disorders to include in the RUSP after they have assessed a systematic, evidence-based review assigned by the committee to an external independent group., MPH, a professor of pediatrics at the Ohio State University and division chief of ambulatory pediatrics at Nationwide Children’s Hospital, both in Columbus, led the review group for SMA. Dr. Kemper is also deputy editor of the journal Pediatrics and a member of the U.S. Preventive Services Task Force.
According to Secretary Azar’s summary in his July 2, 2018, letter of acceptance, thesuggested that “early screening and treatment can lead to decreased mortality for individuals with SMA and improved motor milestones.”
Dr. Kemper elaborated in an interview that, “SMA can be detected through newborn screening, and treatment is now available that can not only reduce the risk of death but decrease the development of neurologic impairment. As with adding any condition to newborn screening, public health laboratories will need to develop strategies to incorporate the screening test. The current FDA-approved treatment, nusinersen, is delivered by lumbar puncture into the spinal fluid. In addition, there are exciting advances in gene therapy leading to new treatment approaches.”
Approximately 95% of SMA cases result from the deletion of exon 7 from both alleles of SMN1. (Other rarer cases are caused by mutations in different genes.) Without the SMN protein produced by SMN1, a person gradually loses muscle function.
A similar gene, SMN2, also can produce the SMN protein but in much lower amounts, typically less than 10% of what a person needs. People can, however, have multiple copies of SMN2, which can produce slightly more SMN protein for a slower disease process.
The five types of spinal muscular atrophy are determined according to symptom onset, which directly correlates with disorder severity and prognosis. Just over half (54%) of SMA cases are Type I, in which progressive weakness occurs over the first 6 months of life and results in early death. Only 18% of children with Type I live past age 4 years, and 68% die by age 2 years. Type 0 is rarer but more severe, usually causing fetal loss or early infant death.
Type II represents 18% of SMA cases and causes progressive weakness by age 15 months. Most people with Type II survive to their 30s but then experience respiratory failure and rarely reach their fourth decade. Individuals with Types III and IV typically have a normal lifespan and only begin to see progressive muscle weakness after 1 year old or in adulthood.
Dr. Kemper’s group focused on the three types diagnosed in infancy: types I, II, and III.
Dr. Kemper emphasized in an interview that “it will be critical to make sure that infants diagnosed with SMA through newborn screening receive follow-up shortly afterward to determine whether they would benefit from nusinersen. More information is needed about the long-term outcomes of those infants who begin treatment following newborn screening so we not only know about outcomes in later childhood and adolescence but treatment approaches can be further refined and personalized.”
Nusinersen works by altering the splicing of precursor messenger RNA in SMN2 so that the mRNA strands are longer, which thereby increases how much SMN protein is produced. Concerns about the medication, however, have included its cost – $750,000 in the first year and $375,000 every following year for life – and potential adverse events from repeated administration. Nusinersen is injected into the spinal canal four times in the first year and then once annually, and the painful injections require patient immobilization. Potential adverse events include thrombocytopenia and nephrotoxicity, along with potential complications from repeated lumbar punctures over time.2
Other concerns about the drug include its limited evidence base, lack of long-term data, associated costs with administration (for example, travel costs), the potential for patients taking nusinersen to be excluded from future clinical trials on other treatments, and ensuring parents have enough information on the drug’s limitations and potential risks to provide adequate informed consent.2
Yet evidence to date is favorable in children with early onset. Dr. Bocchini wrote in the letter to Secretary Azar that “limited data suggest that treatment effect is greater when the treatment is initiated before symptoms develop and when the individual has more copies of SMN2.”
Dr. Kemper’s group concluded that screening can detect SMA in newborns and that treatment can modify disease course. “Grey literature suggests those with total disease duration less than or equal to 12 weeks before nusinersen treatment were more likely to have better outcomes than those with longer periods of disease duration.”
“Presymptomatic treatment alters the natural history” of the disorder, the group found, although outcome data past 1 year of age are not yet available. Based on findings from a New York pilot program, they predicted that nationwide newborn screening would avert 33 deaths and 48 cases of children who were dependent on a ventilator among an annual cohort of 4 million births.
At the time of the evidence review, Massachusetts, Minnesota, Missouri, North Carolina, New York, Utah, and Wisconsin initiated pilot programs or whole-population mandated screening for SMA. Of the three states that reported costs, all reported costs at $1 or less per screen.
The research for the evidence review was funded by a Health Resources and Services Administration grant to Duke University, Durham, N.C. No disclosures were provided for evidence review group members.