Quantitative analyses of SMN1 and SMN2 based on real-time lightCycler PCR: fast and highly reliable carrier testing and prediction of severity of spinal muscular atrophy.
Spinal muscular atrophy (SMA) is a common autosomal recessive disorder in humans, caused by homozygous absence of the survival motor neuron gene 1 (SMN1). SMN2, a copy gene, influences the severity of SMA and may be used in somatic gene therapy of patients with SMA in the future. We present a new, fast, and highly reliable quantitative test, based on real-time LightCycler PCR that amplifies either SMN1 or SMN2. The SMN1 copies were determined and validated in 329 carriers and controls. The specificity of the test is 100%, whereas the sensitivity is 96.2%. The quantitative analysis of SMN2 copies in 375 patients with type I, type II, or type III SMA showed a significant correlation between SMN2 copy number and type of SMA as well as duration of survival. Thus, 80% of patients with type I SMA carry one or two SMN2 copies, and 82% of patients with type II SMA carry three SMN2 copies, whereas 96% of patients with type III SMA carry three or four SMN2 copies. Among 113 patients with type I SMA, 9 with one SMN2 copy lived <11 mo, 88/94 with two SMN2 copies lived <21 mo, and 8/10 with three SMN2 copies lived 33-66 mo. On the basis of SMN2 copy number, we calculated the posterior probability that a child with homozygous absence of SMN1 will develop type I, type II, or type III SMA.
Feldkötter
Markus
M
Institute of Human Genetics, University Clinic, Rheinische Friedrich-Wilhelms University Bonn, Bonn, Germany.
Schwarzer
Verena
V
Wirth
Radu
R
Wienker
Thomas F
TF
Wirth
Brunhilde
B
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000483:Alleles; D001483:Base Sequence; D002648:Child; D002675:Child, Preschool; D017362:Cyclic AMP Response Element-Binding Protein; D005260:Female; D018628:Gene Dosage; D020022:Genetic Predisposition to Disease / Q000235:genetics; D005820:Genetic Testing / Q000379:methods*; D006239:Haplotypes / Q000235:genetics; D006579:Heterozygote; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D009134:Muscular Atrophy, Spinal / Q000145:classification / Q000175:diagnosis* / Q000235:genetics* / Q000503:physiopathology; D009154:Mutation / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000235:genetics*; D016133:Polymerase Chain Reaction / Q000379:methods*; D011379:Prognosis; D016601:RNA-Binding Proteins; D015203:Reproducibility of Results; D055532:SMN Complex Proteins; D012680:Sensitivity and Specificity; D016019:Survival Analysis; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein; D013997:Time Factors
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