Determination of SMN1 and SMN2 copy number using TaqMan technology.
Infantile spinal muscular atrophy (SMA) is a neuromuscular disease caused by homozygous deletion of the SMN1 gene in more than 90% of patients. Identification of carriers for the SMN1 deletion is important for diagnostic purposes and for genetic counseling. The current practical implications of SMN2 copy number determination are limited but may be important, for example, for future drug trials. Here we present a new rapid and reliable approach to determine the copy numbers of the SMN1 and SMN2 genes: For differentiation of the two genes, we developed a quantitative test on the basis of TaqMan technology using minor groove binder (MGB) probes. To evaluate the approach in respect to detection of SMN1 deletion carriers, we tested 40 putative carriers as well as 100 controls. We confirmed the carrier status in all individuals; furthermore, the distribution of SMN1 and SMN2 copies in the control cohort corresponded to that published previously. In total, a clear-cut differentiation between the different copy number ranges could be observed for both genes. This distinct differentiation is based on the exact specificity of MGB probes and the parallel analysis of an external reference locus that circumvents the problem of unavoidable deviations in DNA concentrations. The simplicity and reproducibility of the TaqMan assay presented here should facilitate its establishment in molecular diagnostic laboratories. Nevertheless, the applicability of quantitative analyses of SMN copy numbers requires knowledge about its options and limitations, based on the complex nature of the SMN region and the clinical variability of SMA. Therefore, determination of SMN1 and SMN2 copy numbers should only be offered after careful consideration in each case.
Anhuf
Dirk
D
Institute of Human Genetics, RWTH Aachen, Aachen, Germany. danhuf@ukaachen.de <danhuf@ukaachen.de>
Eggermann
Thomas
T
Rudnik-Schöneborn
Sabine
S
Zerres
Klaus
K
D017362:Cyclic AMP Response Element-Binding Protein; D005260:Female; D017353:Gene Deletion; D018628:Gene Dosage; D006580:Genetic Carrier Screening / Q000379:methods; D005817:Genetic Counseling / Q000379:methods; D006801:Humans; D008297:Male; D015335:Molecular Probes / Q000235:genetics; D009134:Muscular Atrophy, Spinal / Q000175:diagnosis / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000235:genetics*; D016601:RNA-Binding Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods*; D055532:SMN Complex Proteins; D014897:Spinal Muscular Atrophies of Childhood / Q000175:diagnosis / Q000235:genetics; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein; D019914:Taq Polymerase
D017362:Cyclic AMP Response Element-Binding Protein; D015335:Molecular Probes; 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; D019914:Taq Polymerase