Combined Newborn Screening for SMA and SCID in Italy Achieves 100% Positive Predictive Value Over Five Years
核心洞察
A five-year prospective pilot study in Liguria, Italy, screened 32,289 newborns for spinal muscular atrophy (搜索) (SMA) and severe combined immunodeficiency (搜索) (SCID) using a single dried blood spot and multiplex real-time PCR, achieving 99.8% uptake.
Ten confirmed diagnoses were made—five SMA and five immunodeficiency cases—with a positive predictive value of 100% and no false positives or false negatives reported during the study period.
All five SMA cases received early disease-modifying therapy; three presymptomatic newborns achieved favorable motor outcomes, while one SMA type 0 case had a poor outcome despite early intervention.
A landmark five-year prospective pilot study in Italy's Liguria region has demonstrated that combining newborn screening for spinal muscular atrophy (搜索) (SMA) and severe combined immunodeficiency (搜索) (SCID) using a single dried blood spot (DBS) is feasible, accurate, and clinically impactful. The program, which ran from September 4, 2021, to August 31, 2025, screened 32,289 newborns—achieving 99.8% uptake—and identified ten confirmed cases with a positive predictive value (PPV) of 100%.
The study, published in the European Journal of Human Genetics, represents Italy's first implementation of an integrated molecular newborn screening protocol for SMA and SCID. It was conducted by researchers at IRCCS Istituto Giannina Gaslini (搜索), the University of Genoa, the Liguria Regional Health Authority, and all ten regional birth centers.
A Streamlined Multiplex Workflow
The screening protocol employed a single 3.2 mm DBS punch obtained via heel prick at 48–72 hours of age. DNA was extracted and analyzed using the Eonis SCID-SMA kit (Revvity), a multiplex real-time PCR assay that simultaneously detects homozygous deletion of SMN1 (搜索) exon 7 (or exons 7 and 8) for SMA and quantifies T-cell receptor excision circles (TRECs) and kappa-deleting recombination excision circles (KRECs) for SCID and B-cell maturation defects. The RPP30 gene served as an internal control.
Population-based cutoffs were derived from the 1st percentile of the distribution in a reference cohort of 3,000 healthy newborns: 223 copies/10⁵ cells for TRECs and 108 copies/10⁵ cells for KRECs. Samples falling below these thresholds, or showing absent SMN1 (搜索) amplification, were considered screen-positive and underwent duplicate re-testing from the same DBS within 24–48 hours.
Of the 32,289 newborns screened, 654 (2.0%) had an initial screen-positive result—649 suspected SCID cases and 5 suspected SMA cases. Following duplicate re-testing, only 38 newborns (0.12%) required a second DBS sample. After analysis of the second sample, 28 suspected SCID cases were classified as screen-negative, while 10 newborns—5 SMA and 5 SCID cases—remained screen-positive and were referred for confirmatory evaluation. All ten were subsequently confirmed by diagnostic testing.
SMA Outcomes: Early Treatment, Divergent Trajectories
Among the five confirmed SMA cases, four received early disease-modifying therapy with favorable outcomes. The first case, diagnosed in November 2021, was a female newborn with SMA type 1 identified at 15 days of life. Genetic testing confirmed homozygous deletion of SMN1 (搜索) exons 7 and 8 with two SMN2 (搜索) copies. Gene therapy was initiated on day 26 without adverse effects, and follow-up assessments demonstrated normal developmental milestones, including independent walking by 17 months.
A third case, an asymptomatic male newborn with three SMN2 (搜索) copies identified in December 2023, began nusinersen therapy on day 14. Two additional female newborns, each harboring four SMN2 copies and identified in June 2024 and April 2025, started risdiplam therapy on days 25 and 13, respectively, while remaining asymptomatic.
However, the program also illustrated the limits of early intervention. In May 2022, a full-term female newborn with reduced spontaneous movements was diagnosed with SMA type 0, confirmed by homozygous SMN1 (搜索) deletion and a single SMN2 (搜索) copy. Despite early suspicion, the newborn died within days of birth. As the authors note, "the clinical course of the SMA type 0 case in our cohort highlights that for phenotypes with prenatal onset, even the most rapid postnatal risk-stratification and intervention may be insufficient to alter the disease trajectory."
Immunodeficiency Findings: Beyond SCID
The combined TREC/KREC assay identified two cases of adenosine deaminase (ADA)-related SCID, the primary target condition. One case, identified in August 2023, involved a female newborn recalled at 7 days with undetectable TREC and KREC levels. Genetic testing confirmed homozygosity for a pathogenic ADA variant, and a novel homozygous variant in CD3G was also identified—suggesting a rare dual molecular diagnosis. Enzyme replacement therapy was initiated on day 12. A fifth case, identified in October 2024, was a male newborn with compound heterozygous ADA variants; enzyme replacement therapy was started promptly and gene therapy was administered at 8 months.
The assay also detected three clinically significant secondary findings: one case of idiopathic T-cell lymphopenia, one case of DiGeorge syndrome (搜索) (confirmed by heterozygous deletion of TBX1 at 22q11.2), and one case of transient B-cell lymphopenia. The authors argue that identifying such non-SCID lymphopenias "holds substantial clinical utility, as it allowed for specialized immunological follow-up and the implementation of precautionary measures, such as the avoidance of live-attenuated vaccines."
Timeliness and Performance
The median age at clinical recall was 13 days (range 7–22). Positive results were communicated to clinical units within 24 hours, ensuring assessment within 24–48 hours. The median time from recall to genetic diagnosis was 14 days for immunodeficiencies (range 12–26). No false positives and no false negatives were reported during the five-year study period.
Region-specific birth prevalence was estimated at 1:6,433 live births for SMA and 1:16,084 for SCID, consistent with recent Italian and European studies.
Limitations and Future Directions
The authors acknowledge several limitations, including the single-region design, small sample size, lack of formal cost-effectiveness analysis, and short-term follow-up. They emphasize that while the program demonstrates clinical utility in identifying non-SCID lymphopenias, these should be managed as secondary findings rather than primary screening targets. "Future studies should evaluate national scale-up, harmonization of protocols, cost-effectiveness, long-term outcomes, and potential inclusion of additional treatable conditions," the researchers conclude.