Understanding the Four Types of Spinal Muscular Atrophy (SMA)
This overview explains the four types of spinal muscular atrophy, highlighting their symptoms, onset, and genetic factors. Advances in research have improved survival rates, especially in severe forms like Type 1 SMA. Understanding these types helps healthcare providers tailor treatment and management strategies for affected individuals, from infancy to adulthood.
Understanding the Four Types of Spinal Muscular Atrophy (SMA)
Spinal muscular atrophy (SMA) is a rare genetic disorder impacting muscle control, affecting approximately one in 6,000 to 10,000 individuals. It stems from gene mutations, with variations in symptoms, onset, and progression. To aid healthcare providers, SMA is categorized into four types:
Type 1 SMA – Also called infantile SMA or Werdnig-Hoffmann disease, this most common form results from having only two copies of the SMN2 gene. Symptoms appear within the first six months, including weak crying, difficulty swallowing, breathing issues, hypotonia, and poor muscle control. Although historically fatal early on, advances have improved survival rates.
Type 2 SMA – Known as intermediate SMA, patients usually have at least one SMN2 gene. Symptoms emerge between 7-18 months with signs like difficulty standing, muscle weakness, scoliosis, coughing, and finger tremors. Many survive into adulthood, though it can shorten lifespan.
Type 3 SMA – Often called late-onset or mild SMA, individuals typically have 4-8 copies of SMN2. Symptoms start after 18 months, around age 3, including challenges in standing, balance issues, scoliosis, and trouble climbing stairs. Life expectancy usually remains unaffected, but obesity risk can increase.
Type 4 SMA – The adult-onset form occurs after age 35, with 4-8 SMN2 copies. Symptoms include hand and foot weakness, difficulty walking, and muscle twitching, making it the rarest version of SMA.
