Not so long ago, the medical establishment
recognized four types of spinal
muscular atrophy (SMA) — Types 1, 2, 3, 4.
Today, most SMA-related organizations,
including Cure SMA and the Muscular
Dystrophy Association (MDA), recognize
five types.

Type 0 (Zero) is the most severe form of
SMA, according to the Cure SMA description
of the different types.

“Symptoms begin prior to birth and
is seen as decreased fetal movement in
the weeks prior to delivery,” the Cure
SMA Web site says. “At birth, the infant
has severe weakness and often difficulty
breathing, feeding, and may have joint
contractures and cardiac defects. These
infants typically require respiratory and
feeding support prior to confirming the
diagnosis. These infants may survive a few
months.”

Cure SMA notes that SMA Type 1,
sometimes called Werdnig-Hoffmann
disease, “is the most common (60 percent)
and severe form, usually diagnosed during
an infant’s first six months.… If not treated,
Type 1 can be fatal early on in life.”

Type 2 “is usually diagnosed after 6
months of age, but before 2 years of age,”
and while people with SMA Type 2 can
usually sit without support, “they are unable
to walk and will require a wheelchair.”

Type 3 is “usually diagnosed after 18
months of age, but before 3 years of
age” and can be diagnosed in a person’s
teens, Cure SMA said: “Individuals with
SMA Type 3 are initially able to walk, but
have increasingly limited mobility as they
grow, and eventually, many need to use a
wheelchair.”

Type 4, which Cure SMA says consists
of less than 1 percent of all cases, usually
presents after age 35 and results in “mild
motor impairment.”