Table 1 Classification and prognosis of different types of autosomal recessive proximal spinal muscular atrophy[1, 2]

Ia

more severe

prenatal (30%) to 3-6 months

unable to roll over or sit

< 30 months = 100%

< 18 months = 95%

< 7 months = 50%

Ib

less severe

like Ia

like Ia

2.5 - 20 years *

II

intermediate

birth -18 months

sitting

2.5 - 30 years *

IIIa

mild, retarded motor development

to 3 years

walking

4th – 6th decade, usually normal

IIIb

mild, normal motor development

> 3 - 30 years

walking

IV

adult

> 30 years

walking

normal