Table 1.

Clinical classification of spinal muscular atrophy

SMA type	OMIM number	Age of onset	Highest achieved motor function	Natural age of death
0	-	Prenatal/ Foetal	Nil	<6 months
I	253300	<6 months	Sit with support only	<2 years
II	253550	6–18 months	Sit independently	>2 years
III	253400	>18 months	Stand and walk	Adulthood
IV	271150	Adult (2nd or 3rd decade)	Walk during adulthood	Adult

OMIM Online Mendelian Inheritance in Man