. 2017 Jul 20;24(9):529–533. doi: 10.1038/gt.2017.52

Table 1. SMA clinical classification according to onset, achieved milestones, evolution and SMN2 genotype based on experience and previous reports^{29, 30, 31, 32}.

SMA type	Onset	Milestones achieved	Evolution / natural history	Typical SMN2 copy number
1 A (also referred as type 0)	Prenatal	None	Death in weeks, contractures, cardiopathy	1
1B	<3M	Poor or absent head control	Feeding and respiratory problems, linear decline. Death by second or third year of life	2
1C	>3M	Cephalic control	Feeding and respiratory problems. Plateau in first two years	3
2	>6M	Able to sit unaided	Scoliosis. Survival to adolescence/adulthood Weaker cases may lose sitting capability (2a) and stronger cases may stand with support (2b)	3
3a	Between 18 and 36 months	Walking unaided	Scoliosis Early loss of ambulation Normal lifespan	3
3b	>3 years	Walking unaided	Later loss of ambulation Normal lifespan	3–4
4	Second or third decade of life	Walking unaided	Ambulant until late in life Normal lifespan	4

Table 1. SMA clinical classification according to onset, achieved milestones, evolution and SMN2 genotype based on experience and previous reports 29, 30, 31, 32 .