Review article
Spinal muscular atrophy: untangling the knot?
Ivan Biros, Susan Forrest
The
Murdoch Institute, Royal Children's Hospital, Parkville 3052, Melbourne, Australia
Correspondence to: Dr Biros.
Spinal muscular atrophy (SMA), a clinically and genetically
heterogeneous group of neuromuscular diseases, is a disorder of motor
neurones characterised by degeneration of spinal cord anterior horn
cells and muscular atrophy.
SMA is an autosomal recessive disorder with a carrier frequency of
about 1/50. Three candidate genes, the survival motor neurone (SMN)
gene, the neuronal inhibitory protein (NAIP) gene, and the p44 (subunit
of basal transcription factor TFIIH) gene, have been considered as
genes involved in this condition. The region spanning these genes has a
complex organisation including duplications, repetitive sequences,
truncated genes, and pseudogenes, which makes molecular analysis of
this condition difficult. Although deletions have been found in the
majority of SMA patients, a few microrearrangements (like duplications,
missense mutations, microdeletions, and gene conversions) localised in
the telomeric form of the SMN gene have also been reported.
The function of the protein encoded by the SMN gene is still
not fully understood but recent studies have indicated that it is found
intracellularly in gems, novel nuclear structures. Its interaction with
other proteins suggests a role in mRNA processing and metabolism.
Whether the NAIP gene protein and other apoptosis associated proteins
are directly involved in the initial stages of neurone degeneration and
apoptosis, or acting downstream on the pathological pathway, has been
difficult to determine. Further studies will be required to elucidate
possible functional interactions between these proteins.
Keywords: SMA; SMN; NAIP
© 1999 by J Med Genet
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