Spinal muscular atrophy type 1

Werdnig-Hoffmann disease, infantile spinal muscular atrophy, SMA type 1


Spinal muscular atrophy type 1( also known as Werdnig-Hoffmann disease, infantile spinal muscular atrophy, and SMA type 1) is a rare form of spinal muscular atrophy (SMA) presenting in infants. It is an autosomal recessive condition characterised by the degeneration of anterior horn cells, leading to profound symmetrical weakness and wasting of voluntary muscle . It is the second most common lethal autosomal recessive disease of white populations after cystic fibrosis.

 Spinal Muscular Atrophy type 1 describes a subset of SMA and is distinguished by:

The age at presentation (before 6 months).
Severity (death from respiratory failure, typically by the age of 2).

Symptoms - Spinal muscular atrophy type 1

During pregnancy:

  • Reduced fetal movements during the last trimester in 30%.

At birth:

  • Floppy baby (60%).
  • Prolonged cyanosis.


  • Severe weakness.
  • Respiratory difficulties.
  • Difficulty in sucking and/or swallowing.
  • Tongue fasciculations.
  • Poor head control.
  • Facial weakness.
  • Absent reflexes.
  • Congenital joint contractures.
  • Lack of normal motor movements.

Causes - Spinal muscular atrophy type 1

The survival motor neuron 1 (SMN1) gene is missing in 93% of all SMA patients and in 50% of cases there will also be absence of both homologues of the neighbouring gene - neuronal apoptosis inhibitory protein (NAIP).

Prevention - Spinal muscular atrophy type 1

Parents may wish to have genetic counselling before considering any further pregnancies. Prenatal testing has been available since 1998 for families who have had an affected child.

Diagnosis - Spinal muscular atrophy type 1

  • Serum creatine kinase levels - they are usually normal but may be raised.
  • Genetic studies.
  • Electromyogram (EMG) - may be difficult to interpret in young infants - may see evidence of denervation and reinnervation with normal conduction velocities.
  • Muscle biopsy.

Prognosis - Spinal muscular atrophy type 1

The outlook for children with spinal muscular atrophy type 1 is very poor:

  • Median survival is seven months and 95% of children with the disease have died by the age of 18 months.
  • Prognosticating for individual children is difficult however - several studies have cited individual cases where children have had onset of symptoms before the age of 6 months and not developed respiratory failure for years. The genetic basis of this phenotypic variability is not understood.
  • Non-invasive respiratory support and prompt treatment of respiratory complications also appear to prolong survival but not to alter the disease course.

Treatment - Spinal muscular atrophy type 1

No specific therapy is yet available for the treatment of spinal muscular atrophy type 1. Treatment is not disease-modifying. Affected children should be under the care of a multidisciplinary team with expertise in the management of type 1 SMA.


  • Support for the family throughout the lifetime of the child and beyond. Contact with other affected families can be helpful. Children's hospices can offer friendship and respite for affected families.
  • The child may benefit from physiotherapy and respiratory support for the relief of symptoms. How aggressive respiratory management should be is controversial: opinion and practice vary from offering no respiratory support to the use of tracheostomy and long-term invasive ventilation. Others occupy a middle position, suggesting measures such as the use of non-invasive ventilation. The ethical dilemma in deciding what is in the child, the family and society's best interest is great. Families need to be involved in these decisions and helped to understand the long-term implications of ventilation.
  • Only motor function is affected in these children. Sensation and intellect are normal, so encouraging physical contact and interaction is important, for the well-being of the child and parents.
Spinal Muscular Atrophy type 1 is an orphan disease. However, molecular genetics offer potential targets for drug therapy and the hope of gene therapy. A clinical trial network is being established.

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