Inverse correlation between SMN1 and SMN2 copy numbers: evidence for gene conversion from SMN2 to SMN1.
Most carriers of autosomal recessive spinal muscular atrophy (SMA) have only one copy of SMN1 because of SMN1 gene deletions or gene conversions from SMN1 to SMN2, which has only one base difference in coding sequence from SMN1. Using SMN gene dosage analysis, we determined the copy numbers of SMN1 and SMN2 in the general population as well as in SMA patients and carriers. Increased SMN1 copy number is associated with decreased SMN2 copy number in the general population; that is, SMN2 copy number was decreased to one or zero copies in 11 of 13 individuals with three or four copies of SMN1, whereas only 71 of 164 individuals with two copies of SMN1 had one or zero copies of SMN2 (P<0.01). SMN2 copy number was increased to three or four in a subset of SMN1 deletion/conversion carriers, and in most SMA patients with a milder phenotype. In conclusion, our data provide evidence that gene conversion from SMN2 to SMN1 occurs, and that SMN1 converted from SMN2 is present in the general population.
Ogino
Shuji
S
Department of Pathology, Brigham and Women's Hospital, Boston, MA 02115, USA. sogino@partners.org
Gao
Sizhen
S
Leonard
Debra G B
DG
Paessler
Michele
M
Wilson
Robert B
RB
D017362:Cyclic AMP Response Element-Binding Protein; D005785:Gene Conversion / Q000235:genetics*; D018628:Gene Dosage; D005820:Genetic Testing; D006801:Humans; D009134:Muscular Atrophy, Spinal / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000235:genetics*; D016601:RNA-Binding Proteins; D055532:SMN Complex Proteins; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein
D017362:Cyclic AMP Response Element-Binding Protein; D009419:Nerve Tissue Proteins; D016601:RNA-Binding Proteins; D055532:SMN Complex Proteins; C526471:SMN1 protein, human; C526477:SMN2 protein, human; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein