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Table 4 Adult phenotypes of spinal muscular atrophy

From: Health, wellbeing and lived experiences of adults with SMA: a scoping systematic review

Functional classificationaNon-sittersSittersWalkers
Traditional classificationbTypes I, II and some IIIaType II and some IIIaType IIIb, IV and some IIIa
Physical manifestationsVery severe weakness:
-Weakness of face and bulbar muscles
-Small movements of distal limb muscles
Very severe weakness:
-Distal arm movement
Pattern of weakness:
Reduced or absent reflexes in legs, may be normal in arms
Calf hypertrophy
No facial or bulbar weakness
Complications/ comorbidities-Severe restrictive respiratory disease
Ventilator support, Recurrent pneumonia/aspiration
-Severe scoliosis /spinal fusion
Respiratory disease
Non-invasive ventilation
Normal respiratory function
  1. a Functional classifications compiled from adult SMA descriptions in the literature [2, 22, 25,26,27]
  2. b Traditional SMA classifications: Type I - symptom onset < 6 months, unable to sit independently; Type II - symptom onset between 6 and 18 months, achieved ability to sit independently; Type IIIa - symptom onset < 3 years, achieved ability to walk independently; Type IIIb – symptom onset > 3 years, achieved ability to walk independently; Type IV - adult onset SMA