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At a glance

It is an autosomal recessive juvenile spinal muscular atrophy characterized by slowly progressive muscular weakness and atrophy of the upper and lower limbs. It is caused by the degeneration of anterior horn cells (spinal motor neurons). The onset of the disease is during childhood, particularly between the ages of 2 and 17 years. Early symptoms consist of atrophy and weakness of the proximal muscle of the extremities (mainly legs), followed by thoracic muscles. Should not be confused with muscular dystrophy syndromes.


Kugelberg-Welander Syndrome; Juvenile Type Muscular Atrophy Syndrome; Neurogenic Familial Girdle Muscular Atrophy, Type K-W; Spinal Muscular Atrophy Type III; Juvenile Spinal Muscular Atrophy.


This is a medical condition that belongs to a group of spinal cord muscular dystrophy classified into four types that are determined by the age at onset and clinical severity.

  • Spinal Muscular Atrophy Type 1 (SMA I; Werdnig-Hoffman Disease, Infantile Spinal Muscular Atrophy Syndrome): It is the most severe form of the disorder and is usually associated with death during childhood.

  • Spinal Muscular Atrophy Type 2 (SMA II; Intermediate Spinal Muscular Atrophy Syndrome): It is defined clinically as the intermediate form (between SMA I and III), which they designated SMA II, with an onset between 3 and 15 months and usually survival until adolescence even later. Proximal muscle weakness is the cardinal feature.

  • Spinal Muscular Atrophy Type 3 (SMA III; Juvenile Spinal Muscle Atrophy Syndrome; Wohlfart-Kugelberg-Welander Syndrome): It is defined as the juvenile form with an onset during childhood or adolescence.

  • Spinal Muscular Atrophy Type 4 (SMA IV; Adult Spinal Muscular Atrophy Syndrome): It is characterized by an adult-onset spinal muscular atrophy. The median age at onset is around 35 years with the first clinical signs of muscular atrophy by the age of 37 years. This is the most benign form with a symmetrical involvement of the proximal muscles. There is no atrophy of the distal musculature. It is believed to be inherited as an autosomal recessive inheritance.


Neurological disorder resulting from degeneration of anterior horn cells. Kugelberg-Welander Spinal Muscular Atrophy is the least severe of the three forms of spinal muscular atrophy.


It is believed at 1:15,000 live births in the general population. The genetic carrier prevalence is 1:80. Both sexes are affected with a more severe manifestation in males.

Genetic inheritance

Mostly autosomal recessive; some families with autosomal dominant inheritance; very rarely, X-linked transmission. Gene map location (usually) is 5q13.


Degeneration of anterior horn cells.


Blood DNA analysis, electromyography, and muscle biopsy.

Clinical aspects

Onset at the age of ...

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