Kugelberg-Welander disease

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Spinal Muscular Atrophy refers to a group of hereditary diseases that damages and kills specialized nerve cells in the brain and spinal cord (called motor neurons). Motor neurons control movement in the arms, legs, face, chest, throat, and tongue, as well as skeletal muscle activity including speaking, walking, swallowing, and breathing.

Cause

The most common form of SMA is caused by an abnormal or missing gene known as the survival motor neuron gene 1 (SMN1), which is responsible for the production of a protein essential to motor neurons.

Types

This form of SMA has four types:

Type l, also called Werdnig-Hoffman disease or infantile-onset SMA, is usually evident before 6 months of age. The most severely affected children will have reduced movement and chronic shortening of muscles or tendons (called contractures). Other children may have symptoms including reduced muscle tone, lack of tendon reflexes, twitching, skeletal abnormalities, and problems swallowing and feeding. Without treatment, many affected children die before age 2 years.

SMA Type ll is usually first noticed between the 6 and 18 months of age. Children can sit without support but are unable to stand or walk unaided. Children also may have respiratory difficulties. Life expectancy is reduced but most individuals live into adolescence or young adulthood.

SMA Type lll (Kugelberg-Welander disease) is seen after age 18 months. Children can walk independently but may have difficulty walking or running, rising from a chair, or climbing stairs. Other complications may include curvature of the spine, contractures, and respiratory infections. With treatment, most individuals can have a normal lfespan.

Individuals with SMA Type IV develop symptoms after age 21 years, with mild to moderate leg muscle weakness and other symptoms.

Treatment

There is no cure for SMA. Treatment consists of managing the symptoms and preventing complications.

The U.S. Food and Drug Administration has approved the drug nusinersen (Spinraza ™) to treat children and adults with spinal muscular atrophy. The drug is designed to increase production of the full-length SMN protein, which is critical for the maintenance of motor neurons.

In May 2019, the FDA approved onasemnogene abeparovec-xioi (Zolgensma ™) gene therapy for children less than 2 years old who have infantile-onset SMA. A safe virus delivers a fully functional human SMN gene to the targeted motor neurons, which in turn improves muscle movement and function, and also improves survival. In August 2020, the FDA approved the orally-administered drug risdiplam (Evrysdi) to treat patients age two months of age and older with SMA.

Supportive care

Physical therapy, occupational therapy, and rehabilitation may help to improve posture, prevent joint immobility, and slow muscle weakness and atrophy. Stretching and strengthening exercises may help reduce spasticity, increase range of motion, and keeps circulation flowing. Some individuals require additional therapy for speech, chewing, and swallowing difficulties. Applying heat may relieve muscle pain.

Assistive devices

Assistive devices such as supports or braces, orthotics, speech synthesizers, and wheelchairs may help some people retain independence. Proper nutrition and a balanced diet are essential to maintaining weight and strength Non-invasive ventilation at night can prevent apnea in sleep, and some individuals may also require assisted ventilation due to muscle weakness in the neck, throat, and chest during daytime.

Prognosis

The prognosis varies on the form and type of SMA. Some forms are fatal without treatment. People may appear to be stable for long periods, but improvement should not be expected without treatment. Some children with SMA die in infancy while others can live into adolescence or young adulthood. poor for babies with SMA Type I. Most die within the first two years. For children with SMA Type II, the prognosis for life expectancy or for independent standing or walking roughly correlates with how old they are when they first begin to experience symptoms - older children tend o have less severe symptoms Life expectancy is reduced but some individuals live into adolescence or young adulthood. With care, some affected individuals may have a normal lifespan.

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Classification	ICD-10: G12.0 -G12.1 ICD-9-CM: 335.0 -335.1 OMIM: 253300 Online Mendelian Inheritance in Man (OMIM) 253550 Online Mendelian Inheritance in Man (OMIM) 253400 Online Mendelian Inheritance in Man (OMIM) 271150 MeSH: D014897 DiseasesDB: 14093
External resources	MedlinePlus: 000996 GeneReviews: Spinal Muscular Atrophy

• Kugelberg-Welander disease at Curlie

• SMA at NINDS