Werdnig-Hoffmann disease is a type of spinal muscular atrophy (SMA), a rare form of motor neuron disease. It is the most common type of SMA and accounts for about 80% of individuals with this condition. There are 4 types of SMA. Werdnig-Hoffmann disease, also known as SMA1, is the most severe form. Infants with this condition experience severe muscle weakness with onset before 6 months of age and presenting symptoms include severe motor weakness, poor muscle tone, and lack of motor development.
Motor neuron disease is a condition that affects the anterior horn cells of the motor neurons. These are the neurons that control voluntary muscle control. These are rare conditions that are often very severe, and no cure is available. Examples of motor neuron diseases include amyotrophic lateral sclerosis (ALS), progressive muscular atrophy (PMA), SMA, progressive bulbar palsy (PBP), primary lateral sclerosis (PLS), etc., These conditions spare sensory nerves, and individuals do not have sensory involvement. Individuals often have a combination of upper and lower motor neuron symptoms.
SMA is a type of motor neuron disease. SMA presents four subtypes.
Werdnig-Hoffmann disease, also known as acute spinal muscular atrophy, is SMA 1.
SMA2, also known as intermediate SMA and chronic infantile SMA, has less severe symptoms than SMA1 and can sit without support but cannot stand or walk. SMA2 symptom onset is in infanthood.
SMA3, also known as Kugelberg-Welander disease, presents after the age of 1, and the child is able to walk initially but later has the regression of motor abilities. They often develop poor balance, falls, and scoliosis.
Individuals with SMA4 have minimal symptoms compared to the other forms, and symptom onset is after the age of 10 years. They usually have a normal lifespan. They usually have normal motor milestones and mobility.
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