GTR Home > Conditions/Phenotypes > Spinal muscular atrophy


Spinal muscular atrophy (SMA) is characterized by progressive muscle weakness resulting from degeneration and loss of the anterior horn cells (i.e., lower motor neurons) in the spinal cord and the brain stem nuclei. Onset ranges from before birth to adolescence or young adulthood. Poor weight gain, sleep difficulties, pneumonia, scoliosis, and joint contractures are common complications. Before the genetic basis of SMA was understood, it was classified into clinical subtypes; however, it is now apparent that the phenotype of SMA associated with disease-causing mutations of SMN1 spans a continuum without clear delineation of subtypes. Nonetheless, classification by age of onset and maximum function achieved is useful for prognosis and management; subtypes include: SMA 0 (proposed), with prenatal onset and severe joint contractures, facial diplegia, and respiratory failure; SMA I, with onset before age six months; SMA II, with onset between age six and 12 months; SMA III, with onset in childhood after age 12 months and ability to walk at least 25 meters achieved; and SMA IV, with adult onset. [from GeneReviews]

Associated genes

  • Also known as: SIP1, SIP1-delta, GEMIN2
    Summary: gem (nuclear organelle) associated protein 2

  • Also known as: SMNR, SPF30, TDRD16C, SMNDC1
    Summary: survival motor neuron domain containing 1

Go to complete MedGen record for Spinal muscular atrophy

Clinical resources

Practice guidelines

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