Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) (synonyms: proximal spinal muscular atrophy; ICD-10-GM G12.-: Spinal Muscular Atrophy and Related Syndromes) is a genetic autosomal recessive muscle disease that manifests in utero up to 40 years of age, depending on severity. It is characterized by progressive decline of motor neurons within the anterior horn of the spinal cord. This results in muscle atrophy.

The severity of spinal muscular dystrophy can be divided into:

SMA type Synonyms/ICD-10-GM Start Motor skills Clinical findings Survival
0 neonatal form congenital reduced fetal (infantile) movements respiratory disturbances at birth Early lethal (fatal) if not ventilated immediately from birth
1 Acute infantile SMA; ICD-10-GM G12.0: Infantile spinal muscular atrophy, type I [Werdnig-Hoffmann type]. Within the first 6 months of life Unable to sit, stand or walk freely; Severe muscular hypotonia (“floppy infant”), powerless crying, weak/reduced coughing, dysphagia (dysphagia of swallowing) with pseudohypersalivation (here, there is no increased salivation due to increased saliva production, but an inability to swallow saliva effectively to required degree) Early death (due to respiratory insufficiency (respiratory failure due to failure of external (mechanical) breathing) and aspiration (entry of material (e.g., saliva/food) into the respiratory tract
2 Chronic infantile SMA; intermediate SMA; ICD-10-GM G12.1: other inherited spinal muscular atrophy 7-18 months of age Sitting freely is possible, but dependent on walking aids;standing and walking not possible Delayed motor development, poor thriving, fine-beat hand tremor (hand tremor), weak/reduced cough thrust, respiratory insufficiency (respiratory weakness) as it progresses;

Scoliosis (lateral curvature of the spine) and joint contractures (joint stiffness).

>10 years after onset of disease in 90%.
3 Kugelberg-Welander (juvenile SMA); ICD-10-GM G12.1: Other hereditary spinal muscular atrophy. > 18 months of age Free standing and walking is learned Variable expression of muscle weakness and atrophy; loss of walking ability is possible over time Life expectancy is not significantly reduced
3a < 3 years
3b > 3 years
4 Adult SMA; ICD-10-GM G12.1: other inherited spinal muscular atrophy. <30 years of age Free standing and walking is learned Mild course with usually preserved ability to walk Life expectancy not reduced

Sex ratio: slightly more common in boys than in girls.

The prevalence (disease incidence) is estimated at about 1: 80,000 and the annual incidence at about 1: 10,000.SMA type 1: 1-9/100,000; SMA type 3: 1-9/100,000.

In Germany, approximately one in 6,500 newborns is affected (mutation in the SMN1 gene).

The incidence (frequency of new cases) is about 13 cases per 100,000 population per year.

Course and prognosis: see table above

Lethality: see table above

Comorbidities: orthopedic complications due to bone and joint problems (types 1, 2), muscle weakness (types 1, 2), joint contractures/joint stiffness (types 1, 2), ankylosis (joint stiffness) of the mandible (types 1, 2, 3), and scoliosis/lateral curvature of the spine (type 3)