(Juvenile SMA or Kugelberg-Welander disease)
Type 3 SMA varies in severity according to the age first diagnosed, though children tend to be diagnosed anywhere between 18 months of age and early adolescence. Most are diagnosed before the age of three.
Most children with SMA III can stand and walk but have trouble with motor skills, such as going up and down stairs; their varying degrees of muscle weakness may be so mild that medical attention is not sought for years. Early milestones are usually reached. Most will show difficulty walking at some stage, though toddlers and children will fall frequently, have difficulty getting up from a sitting position, or be unable to run, whereas others may be diagnosed in late adolescence or early adulthood. The lower extremities are often more severely affected than the upper extremities
Feeding and swallowing difficulties in this type of SMA are less common than type 2, though may occur. Muscle aches and symptoms of joint overuse are common. The disease progresses slowly, and the overall course is mild. Many patients have normal life expectancies.
(Adult Onset Spinal Muscular Atrophy)
Symptoms of type 4 are usually not noticed until early to late adulthood (mid 30’s ).
Symptoms include generalized weakness and muscle wasting with muscle twitches common, atrophy of distal leg muscles, thigh muscle weakness, distal arm muscle weakness, impaired vibratory sense, variable diminished leg deep tendon reflexes, no cortical spinal tract dysfunction. The bulbar muscles used for swallowing and respiratory function are rarely affected in SMA-4.
In many ways, the disease mimics the symptoms of type III, with the progression of muscle weakness getting worse over time.
Loss or reduced function in the limbs is usually mild and respiratory or gastrointestinal problems are rare. People with type 4 have a normal lifespan, and only a small proportion of people will need wheelchair assistance.