What is the clinical evidence from this study?

Study design: Other. Population: Spinal muscular atrophy (SMA) Types I, II, and III. Primary outcome: Estimated number of prevalent cases of SMA Types I, II, and III in the US in 2016.

What does this research mean for the field?

Using indirect life table methods, the estimated number of people living with spinal muscular atrophy Types I, II, and III in the United States ranges from 8,526 to 10,333. Novelty: ClaimNovelty.SYNTHESIS. Consensus alignment: ConsensusAlignment.NEUTRAL.

November 28, 2017Open Access

Indirect estimation of the prevalence of spinal muscular atrophy Type I, II, and III in the United States

Key Result

Using indirect life table methods, the estimated number of people living with spinal muscular atrophy Types I, II, and III in the United States in 2016 ranges from 8,526 to 10,333.

Structured PICO

Population

United States population (infants born with an SMA genotype)

Outcome

Prevalence of spinal muscular atrophy (SMA) Types I, II, and III

Indirect estimation using life tables provides the first evidence-based estimates of the number of people living with SMA in the United States.

Limitations

Survival was assumed to be negligible after 25 years in patients with SMA Type I and 50 years in patients with SMA Type II
Survival expected for each year of life among those with SMA have not been reported, requiring an assumption of constant decline between reporting periods
Standard of care demonstrates great variability so that survival in different periods is probably not constant
Selection bias may be of concern in the published studies if patients receiving more aggressive care were more likely to participate

Abstract

BACKGROUND: Spinal muscular atrophy (SMA) is a progressive, devastating disease and a leading inherited cause of infant mortality. The limited population-based literature is confined to small regional studies. Estimates of prevalence are needed to characterize the burden of SMA and to understand trends in prevalence by disease type as new treatments become available. The reported estimates of SMA genotype prevalence at birth consistently range from 8.5-10.3 per 100,000 live births, with a mid-range estimate of 9.4 per 100,000. Among infants born with an SMA genotype, it is reported that ~58% will develop SMA Type I, 29% will develop Type II, and 13% will develop Type III, respectively. RESULTS: Using evidence from peer-reviewed literature for SMA birth prevalence, age at symptom onset, and SMA type-specific survival, and incorporating United States vital statistics, we constructed life tables to estimate prevalence for SMA Types I, II, and III in the United States. We estimated the number of prevalent cases in the US to be 8526, 9429, and 10,333 based on a birth prevalence of 8.5, 9.4, and 10.3, respectively (the lower, midpoint, and upper ends of the reported range). Assuming the midpoint of 9.4 and US-reported survival, the type-specific population prevalence estimates were 1610 for SMA Type I, 3944 for SMA Type II, and 3875 for SMA Type III. Evidence-based estimates of the number of people living with SMA in the United States in the published literature were previously unavailable. CONCLUSIONS: In the absence of a survey or other means to directly estimate prevalence in the US population, estimates can be calculated indirectly using a life table.

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