The Five Types of SMA

holding a baby hand


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.”

This article originally appeared in the Nov/Dec 2021 issue of Mobility Management.

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