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GENATLAS PHENOTYPE
last update : 11/07/2008
Symbol SMA4
Location 5q13.2
Name spinal muscular atrophy, type 4
Corresponding gene SMN1 , SMN2
Main clinical features
  • onset >5 y, walks normally, life expectancy indefinite
  • adult-onset spinal muscular atrophy, median age at onset 35 years, relatively benign, with symmetrical proximal muscle involvement and preservation of the distal musculature
    • Genetic determination autosomal recessive
    Function/system disorder neuromuscular
    Type disease
    Remark(s) SMN1 is considered to be the primary disease causing gene ; SMN2 cannot fully compensate lack of SMN1 expression because most normal SMN2 transcripts lack exon 7; the SMN2 copy number influences disease severity
    Genotype/Phenotype correlations phenotypes in SMN1 mutations span a continuum without clear delineation of subtypes, which are classified by age of onset and maximum function achieved ; SMN2 may have a disease-modifying role in SMA, with a greater SMN2 copy number associated with later onset and better prognosis