Spinal Muscular Atrophy (SMA) is a genetic neuromuscular condition with major differences by type and severity. Key early clinical clues—such as muscle weakness, breathing vulnerability, and characteristic diagnostic findings—guide how SMA is confirmed. This page also covers incidence and screening, how genetic testing works, and what current treatments aim to improve over time.
Key Takeaways
- Hypotonia and symmetric proximal muscle weakness are hallmark signs appearing by 6 months in type 1 SMA
- Respiratory failure occurs in 66% of untreated type 1 SMA infants by 2 years
- Tongue fasciculations present in 85% of type 1 SMA patients at diagnosis
- Electromyography (EMG) shows denervation patterns in 100% of confirmed SMA
- Genetic testing for SMN1 exon 7 deletion has 95-98% sensitivity for SMA diagnosis
- Newborn screening using real-time PCR detects 1.2% false positives for SMA
- Spinal Muscular Atrophy (SMA) has an overall incidence of approximately 1 in 10,000 live births worldwide
- In the United States, SMA affects about 1 in 11,000 live births according to CDC data from 2016-2018
- SMA type 1 accounts for 60% of all SMA cases with an incidence of 1 in 11,000 to 1 in 26,000 live births
- 95% of SMA cases result from homozygous deletion of exon 7 in SMN1 gene
- SMN2 gene copy number inversely correlates with SMA severity: 2 copies typical for type 1
- De novo mutations in SMN1 occur in 2-6% of SMA patients
- Nusinersen treatment increases survival to 93% at 24 months in type 1 vs 8% untreated
- Onasemnogene abeparvovec achieves HFMSE +5.9 points at 14 months in type 1
- Risdiplam improves motor function with +5.2 SMN protein increase in 90% of treated
SMA is common, rapidly progressive, and testable early, with treatments sharply improving survival and motor outcomes.
Related reading
01 · Category
Clinical Features29 stats
01
Hypotonia and symmetric proximal muscle weakness are hallmark signs appearing by 6 months in type 1 SMA
02
Respiratory failure occurs in 66% of untreated type 1 SMA infants by 2 years
03
Tongue fasciculations present in 85% of type 1 SMA patients at diagnosis
04
Scoliosis develops in 100% of non-ambulatory SMA type 2 patients by age 15
05
Areflexia or hyporeflexia in lower limbs seen in 95% of SMA type 3 cases
06
Mean age of death in untreated type 1 SMA is 6.2 months (range 2 days to 25.5 months)
07
Hand tremor at rest observed in 70% of type 2 SMA children over 3 years
08
Ventilatory support required in 38% of type 2 SMA by age 10 years untreated
09
Fatigue and proximal weakness lead to loss of ambulation in 75% of type 3 by adulthood
10
Bulbar dysfunction causes poor feeding in 90% of symptomatic neonates with type 0/1 SMA
11
Hip dislocation occurs in 20% of SMA type 2 patients due to ligament laxity
12
Elevated CK levels (>1000 IU/L) in 30% of SMA patients at onset
13
Paradoxical breathing pattern in 80% of type 1 SMA due to intercostal weakness
14
Contractures develop in 67% of limbs in non-treated type 1 SMA
15
Facial sparing with alert expression in 100% of infantile SMA cases
16
Osteopenia with Z-score <-2.5 in 90% of pediatric SMA patients
17
Sleep disturbances including hypoventilation in 50% of type 2 SMA
18
Weakness peaks at hips (90% affected) then shoulders (80%) in type 2 SMA
19
Kyphosis in 95% of sitting type 2 SMA by age 5
20
Absent deep tendon reflexes in 100% of type 1, 90% type 2, 70% type 3
21
Recurrent chest infections in 70% of type 1 by 1 year
22
Fine motor skills preserved longer than gross in type 3 SMA (80%)
23
Ptosis in 25% of longstanding SMA type 2/3
24
Normal cognition with IQ 90-110 in 95% ambulatory SMA
25
Polyphasic motor units on EMG in 100% biopsied cases
26
Weight-for-length Z-score <-2 in 50% type 1 due to dysphagia
27
Orthostatic hypotension in 15% of older type 3 patients
28
Fibrillations and positive sharp waves on EMG in 80% limbs
29
HFMSE score declines 0.5 points/year untreated type 2
Interpretation
Clinical Features Interpretation
From a clinical features standpoint, untreated type 1 SMA shows an especially severe early trajectory, with respiratory failure in 66% of infants by age 2 and a mean age of death of just 6.2 months, underscoring how rapidly hallmark neuromuscular signs can progress.
More related reading
02 · Category
Diagnosis30 stats
01
Electromyography (EMG) shows denervation patterns in 100% of confirmed SMA
02
Genetic testing for SMN1 exon 7 deletion has 95-98% sensitivity for SMA diagnosis
03
Newborn screening using real-time PCR detects 1.2% false positives for SMA
04
Muscle biopsy reveals group atrophy of type 1 fibers in 85% of SMA cases
05
MLPA detects SMN2 copy number with >99% accuracy in prenatal testing
06
CMAP amplitude <1mV in 90% of type 1 SMA on nerve conduction studies
07
ACMG recommends SMA carrier screening for all reproductive-age individuals
08
Dried blood spot PCR screening identifies SMA in 88% of pre-symptomatic cases
09
Elevated SMN protein in fibroblasts distinguishes carriers from non-carriers at 70% specificity
10
MRI shows spinal cord atrophy in 75% of advanced SMA type 1
11
NGS panels confirm SMA in 2% of undiagnosed neuromuscular cases
12
Prenatal diagnosis via CVS detects SMN1 deletion in 97% accuracy
13
Haplotype analysis resolves 3% of equivocal SMN1 cases
14
Ultrasound fetal movements reduced in 60% of affected pregnancies
15
CHOP INTEND score <40 at birth predicts severe type 1 SMA in 92%
16
SMN1 dosage analysis by qPCR standard in 95% of labs
17
False negative newborn screen rate <0.1% with HRMA method
18
Hammersmith Functional Motor Scale differentiates SMA types with 85% accuracy
19
SNAP amplitude reduced 70% in median nerve of type 1
20
Carrier screening false negative rate 3% due to 2+ SMN1 copies
21
Preimplantation genetic diagnosis prevents 100% SMA births in tested cycles
22
Refined sensory nerve action potentials normal in 95% SMA
23
SMN RT-PCR quantifies full-length transcripts with 80% correlation to phenotype
24
6MWT differentiates type 3a (>150m) from 3b (<100m)
25
Brainstem auditory evoked potentials abnormal in 20% severe SMA
26
Droplet digital PCR improves SMN1 quantification to 99.5%
27
Ejection fraction decreases 10% in untreated advanced SMA heart
28
Bayley-III scores normal in 90% pre-symptomatic SMA infants
29
Anti-SMN antibodies post-gene therapy in 13% patients
30
PedsQL neuromuscular module detects QoL decline early
More related reading
03 · Category
Epidemiology24 stats
01
Spinal Muscular Atrophy (SMA) has an overall incidence of approximately 1 in 10,000 live births worldwide
02
In the United States, SMA affects about 1 in 11,000 live births according to CDC data from 2016-2018
03
SMA type 1 accounts for 60% of all SMA cases with an incidence of 1 in 11,000 to 1 in 26,000 live births
04
The carrier frequency for SMA mutations is 1 in 50 in the general population, leading to 1 in 2,500 carrier-carrier couples having an affected child
05
Prevalence of SMA in Europe is estimated at 5.2 to 9.1 per 100,000 individuals
06
SMA type 2 incidence is around 1 in 19,000 live births, representing 30% of SMA cases
07
Global newborn screening for SMA identifies 1 in 8,000 to 1 in 12,000 infants affected
08
In Australia, SMA incidence from newborn screening (2018-2020) was 1 in 9,319 live births
09
SMA type 3 has the lowest incidence at 1 in 300,000 live births but longer survival
10
Consanguinity increases SMA risk with odds ratio of 4.8 in some populations
11
Annual SMA births in the US estimated at 400-500 before widespread screening
12
SMA prevalence in children under 16 years is 1.6 per 100,000 in the UK
13
Type 0 SMA, the rarest form, has incidence less than 1 in 100,000 live births
14
Carrier screening uptake in at-risk populations reaches 90% in Israel, reducing incidence by 92%
15
SMA accounts for 65% of hereditary neuromuscular diseases in infancy
16
SMA incidence post-screening drops 37% in screened populations
17
Type 1 SMA survival without respiratory support is 8% at 24 months untreated
18
Carrier rate in Caucasians is 1/35-1/50, higher in African populations at 1/90
19
SMA represents 40% of referrals to pediatric neuromuscular clinics
20
Annual global SMA cases estimated at 10,000-25,000 newborns
21
SMA type 4 prevalence <1 per million adults
22
Quebec newborn screening detected 1 in 6,516 for SMA from 2014-2018
23
Male:female ratio in SMA is 1:1 across all types
24
Parental consanguinity in 17% of autosomal recessive SMA cases in consanguineous regions
Interpretation
Epidemiology Interpretation
From an epidemiology perspective, Spinal Muscular Atrophy is relatively rare overall, at about 1 in 10,000 worldwide and roughly 1 in 11,000 live births in the United States, yet it shows a clear concentration in severe disease with type 1 making up 60% of cases, illustrating why tracking incidence and subtype patterns is crucial for public health planning.
More related reading
04 · Category
Genetics26 stats
01
95% of SMA cases result from homozygous deletion of exon 7 in SMN1 gene
02
SMN2 gene copy number inversely correlates with SMA severity: 2 copies typical for type 1
03
De novo mutations in SMN1 occur in 2-6% of SMA patients
04
Intragenic SMN1 mutations found in 5% of compound heterozygous cases
05
SMN2 produces only 10% functional SMN protein compared to SMN1
06
Rare SMN1 duplication alleles complicate carrier testing in 2% of cases
07
NAIP gene deletions co-occur with SMN1 in 45% of type 1 SMA patients
08
SMN1 exon 7 c.840C>T mutation prevalence is 1.6% in compound heterozygotes
09
Telomeric SMN1-to-centromeric SMN2 conversion events cause 40% of atypical cases
10
Modifier genes like PLS3 influence bone density in SMA patients independently of SMN
11
SMNΔ7 protein isoform accumulates in axons, contributing to pathology
12
Heterozygosity for SMN1 point mutations in 4% of severe SMA cases
13
SMN2 copy number >4 ameliorates phenotype in 80% of type 3 cases
14
Biallelic SMN1 deletions confirmed by MLPA in 98% accuracy
15
Rare variants in DDR1 gene modify SMA phenotype in mouse models
16
2% of SMA cases due to SMN1 gene conversion events
17
SMN2 exon 7 inclusion increased 50% by ASOs in vitro
18
Plastin 3 (PLS3) overexpression rescues SMA phenotype in 30% of families
19
BACH1 modifier gene variants protect against severe SMA in 15%
20
SMN1 c.*3+80T>G SNP associated with milder phenotype
21
UBA1 variants exacerbate SMA in mouse models by 20% severity
22
SMN2 copy number 3 in 20% type 1, 40% type 2, 80% type 3 patients
23
Heteroduplex analysis detects 92% of SMN1 point mutations
24
IGHMBP2 mutations mimic SMA in 1% of distal cases
25
Coriell cell lines show SMNΔ7 aggregation in 60% SMA fibroblasts
26
CRISPR editing of SMN2 restores 70% function in iPSCs
Interpretation
Genetics Interpretation
Genetically, most SMA is driven by SMN1 defects with 95% of cases linked to homozygous exon 7 deletion, and the balance between SMN1 and SMN2 matters because SMN2 copy number inversely tracks severity while SMN2 makes only about 10% of functional SMN protein.
More related reading
05 · Category
Treatment25 stats
01
Nusinersen treatment increases survival to 93% at 24 months in type 1 vs 8% untreated
02
Onasemnogene abeparvovec achieves HFMSE +5.9 points at 14 months in type 1
03
Risdiplam improves motor function with +5.2 SMN protein increase in 90% of treated
04
Ventilatory-free survival 79% at 3 years with nusinersen in infants
05
Spinraza (nusinersen) approved for all SMA types, event-free survival 100% at 13 months
06
Gene therapy Zolgensma reduces mortality to 0% at 14 months in early treated
07
Risdiplam FIREFISH trial: 41% sit unsupported at 12 months vs 0% placebo
08
Scoliosis surgery rates drop 50% post-nusinersen in type 2/3
09
SMN protein levels rise 2.2-fold after 4th nusinersen dose
10
Custirsen combination trials show synergistic SMN upregulation in 70%
11
Non-invasive ventilation prolongs life by 3.7 years in type 1 SMA
12
Physical therapy improves CHOP INTEND by 4 points in 60% of type 1
13
Apitegromab (SRK-015) increases HFMSE by 1.8 points in phase 2
14
Early nusinersen before 3 months: 100% event-free vs 64% later
15
Zolgensma one-time infusion costs $2.125M but saves $4.1M lifetime
16
Risdiplam oral dosing improves MFM-32 by 3.6 points in type 2/3
17
Cardiac function preserved in 95% post-gene therapy
18
Bone health interventions reduce fractures by 40% in SMA
19
Nusinersen real-world: 85% ventilator independence at 2 years
20
Long-term nusinersen: 90% maintain motor milestones at 5 years
21
Zolgensma liver enzyme elevation resolves in 90% with steroids
22
Risdiplam SUNFISH: 2.55 point MFM-32 gain vs 0.30 placebo
23
Gastrostomy placement delayed 12 months with early therapy
24
SRK-015 phase 3 TOPAZ: HFMSE +3.6 at 12 months
25
Scoliosis progression slows to 5 degrees/year post-treatment
report visual · Breakdown
Progression & burden of spinal muscular atrophy (SMA)
High rates of respiratory and neuromuscular complications occur in untreated SMA, varying by type.
85%
Tongue fasciculations present in 85% of type 1 SMA patients at diagnosis
15%
Orthostatic hypotension in 15% of older type 3 patients
Reference
Cite This Report
This report is designed to be cited. We maintain stable URLs and versioned verification dates. Copy the format appropriate for your publication below.
APA
Samuel Norberg. (2026, February 13). Spinal Muscular Atrophy Statistics. Gitnux. https://gitnux.org/spinal-muscular-atrophy-statistics
MLA
Samuel Norberg. "Spinal Muscular Atrophy Statistics." Gitnux, 13 Feb 2026, https://gitnux.org/spinal-muscular-atrophy-statistics.
Chicago
Samuel Norberg. 2026. "Spinal Muscular Atrophy Statistics." Gitnux. https://gitnux.org/spinal-muscular-atrophy-statistics.
Sources & references
16 datasets cited across this report · attribution is report-level