Journal
AMERICAN JOURNAL OF MEDICAL GENETICS PART A
Volume 130A, Issue 3, Pages 307-310Publisher
WILEY
DOI: 10.1002/ajmg.a.30251
Keywords
neuromuscular disorder; spinal muscular atrophy; SMN; discordant phenotype
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Funding
- NCRR NIH HHS [UL1 RR025764] Funding Source: Medline
- NINDS NIH HHS [NS41634] Funding Source: Medline
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Spinal muscular atrophy is a common autosomal. recessive neuromuscular disorder caused by the homozygous loss of the SMN1 gene. The absence of the SMN1 gene has been shown to occur in all types of SMA, childhood and adult forms. In rare cases, asymptomatic family members have also been found with homozygous mutations in the SMN1 gene, suggesting a role for phenotypic modifiers. We describe three unrelated asymptomatic individuals, with family histories of SMA, who were shown to have the homozygous SMN1 deletion. Quantitative studies indicated that the three individuals all had increased SMN2 copy numbers. These cases not only support the role of SMN2 in modifying the phenotype, but our data also demonstrate that expression levels consistent with five copies of the SMN2 genes maybe enough to compensate for the absence of the SMN1 gene. Lastly, in cases similar to the ones described, the measurement of the SMN2 gene copy number may provide valuable prognostic information. (C) 2004 Wiley-Liss, Inc.
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