SMA prevalence at birth lower than thought, US study says
The prevalence of spinal muscular atrophy (SMA) at birth in the U.S. is lower than the historic global SMA birth prevalence estimate, according to data from newborn screening programs from 30 U.S. states.
The findings were published as a research letter, “Newborn Screening and Birth Prevalence for Spinal Muscular Atrophy in the US,” in JAMA Pediatrics.
The researchers said the data “may be used to anticipate health care resource use for SMA and to plan future research in SMA care and treatment.”
Several studies have shown that starting SMA disease-modifying therapies as early as possible increases the chances of better outcomes, underscoring the need for prompt diagnosis.
Newborn screening programs to detect SMA at birth are in place in several countries. In the U.S., newborn screening was implemented in 2018 and is now available in 48 states. The procedure uses blood collected from a small heel prick, which is then used to extract DNA and screen for possible conditions with a genetic background, including SMA.
Faulty protein
SMA is caused by low levels of the survival motor neuron (SMN) protein due to mutations in the SMN1 gene. The SMN protein plays a vital role in maintaining the health and function of nerve cells responsible for controlling voluntary muscle movement, ultimately leading to their progressive degeneration.
A second gene, SMN2, also carries instructions to make this protein, although significantly less protein can be made. Still, SMN2 partly compensates for faulty SMN1 in people with SMA, and a higher number of copies equates to greater SMN production and less severe disease with a later onset.
U.S.-based patient advocacy organization Cure SMA, in collaboration with state public health laboratories, used data from newborn screening programs to estimate the birth prevalence of SMA in the U.S.
Data from public health laboratories of 30 of the 48 states conducting SMA newborn screening between January 2018 and December 2022 were included in the analysis.
This corresponded to a total of 6.24 million infants, 425 of whom were diagnosed with SMA, yielding an overall birth prevalence of approximately one SMA case per 14,694 births — lower than the historic global SMA birth prevalence estimate of approximately one in every 10,000 births.
Information on the number of SMN2 gene copies was provided by 21 states. Data from 240 infants showed that 5% had one copy and 49% had two copies. About a third (33%) had three copies, and 13% had four or more.
The authors noted several limitations in their study, including the collection of data at various points after the implementation of statewide SMA newborn screening, which resulted in minimum birth prevalence estimates and variability among states. Additionally, the different data collection time points made it difficult to accurately report the proportion of births covered in the analysis. And the calculation of birth prevalence was limited to data from states that reported the number of infants screened.
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