Skip to
  1. Homepage
  2. Rare diseases
  3. Search
Simple search

Simple search

(*) mandatory field


Other search option(s)

Proximal spinal muscular atrophy type 2

Synonym(s) Chronic infantile spinal muscular atrophy
Chronic spinal muscular atrophy
Intermediate spinal muscular atrophy
SMA type 2
SMA type II
Prevalence 1-9 / 100 000
Inheritance Autosomal recessive
Age of onset Infancy
  • G12.1
MeSH -
MedDRA -


Disease definition

Proximal spinal muscular atrophy type 2 (SMA2) is a chronic infantile form of proximal spinal muscular atrophy (see this term) characterized by muscle weakness and hypotonia resulting from the degeneration and loss of the lower motor neurons in the spinal cord and the brain stem nuclei.


Prevalence is estimated at around 1/70,000. The disease is slightly more frequent in males than in females.

Clinical description

Disease onset occurs between the ages of 6 and 18 months (usually around 15 months). Generally, affected children have difficulty sitting independently and are unable to stand and walk by the age of one year. The muscle weakness (almost always symmetrical) predominantly affects the legs and trunk muscles. Finger trembling is frequent. Respiratory failure, scoliosis, and fractures in response to minimal trauma, are common.


Similarly to the other forms of SMA, SMA2 is primarily caused by deletions in the SMN1 gene (5q12.2-q13.3) encoding the SMN (survival motor neuron) protein. Although there is some variation, disease severity in SMA is inversely correlated with the number of copies of the second SMN gene (SMN2; 5q13.2), with patients with MSA2 having on average three SMN2copies. Deletions of the NAIP (5q13.1) gene have also been identified in SMA2 patients and may play a role in modifying disease severity.

Diagnostic methods

he diagnosis is based on clinical history and examination, and can be confirmed by genetic testing. Electromyography and muscle biopsy may be necessary.

Differential diagnosis

Differential diagnoses include amyotrophic lateral sclerosis, congenital muscular dystrophies, congenital myopathies, primary lateral sclerosis, myasthenia gravis, and carbohydrate metabolism disorders (see these terms).

Antenatal diagnosis

Antenatal diagnosis is possible through molecular analysis of amniocytes or chorionic villus cells.

Genetic counseling

Transmission is autosomal recessive but around 2% of cases are caused by de novo mutations. Genetic counseling should be offered to affected families.

Management and treatment

Clinical trials are ongoing to identify potential drug treatments for SMA2, mainly targeted towards increasing the levels of the full length SMN protein. However, at present, management remains symptomatic, involving a multidisciplinary approach and aiming to improve quality of life. Respiratory support is necessary. Physiotherapy and occupational therapy are recommended. Noninvasive ventilation may be useful. Antibiotic therapy is required in case of pulmonary infection. The scoliosis may require a corset/back brace for support, or need surgical correction.


Life expectancy for patients with SMA2 is variable. With adapted treatment, particularly for respiratory insufficiency, the majority of patients survive up to adulthood, although they will never be able to walk independently.

Expert reviewer(s)

  • Dr Haluk TOPALOGLU

(*) Required fields.

Attention: Only comments seeking to improve the quality and accuracy of information on the Orphanet website are accepted. For all other comments, please send your remarks via contact us. Only comments written in English can be processed.

Captcha image

Detailed information

Summary information
Anesthesia guidelines
Review article
Guidance for genetic testing
Article for general public
Clinical genetics review
Get Acrobat Reader
The documents contained in this web site are presented for information purposes only. The material is in no way intended to replace professional medical care by a qualified specialist and should not be used as a basis for diagnosis or treatment.