SMA carrier testing--validation of hemizygous SMN exon 7 deletion test for the identification of proximal spinal muscular atrophy carriers and patients with a single allele deletion.
To facilitate the detection of carriers of a hemizygous survival motor neuron (SMN) exon 7 deletion we have modified the quantitative SMN exon 7 assay described by McAndrew et al (1997). The major changes include quantitative analysis of the amount of SMN exon 7-specific fluorescently-labelled PCR product on an automated sequencer, and the monitoring of the completeness of a DraI digestion necessary to distinguish the PCR products of exons 7 of SMN and its copy gene. In our method the amount of SMN exon 7 PCR product is compared with the amount of a co-amplified PCR product of the retinoblastoma (RB1) exon containing a DraI restriction site. By co-amplification using the same primers of plasmids included in the reaction as internal standards containing SMN exon 7 with a 36-nucleotide deletion and RB1 exon 13 with a 19-nucleotide deletion, respectively, the relative amplification efficacy can be monitored. The assay has been validated in 63 ascertained carriers and 28 ascertained non-carriers. The sensitivity of the test is approximately 97%, the specificity approaches 100%. In four out of six SMA patients without a homozygous deletion we detected a hemizygous deletion. The implications of the use of this assay for carrier testing and for confirmation of the clinical diagnosis of SMA are discussed.
Scheffer
H
H
Department of Medical Genetics, University of Groningen, The Netherlands. h.scheffer@med.rug.nl
Cobben
J M
JM
Mensink
R G
RG
Stulp
R P
RP
van der Steege
G
G
Buys
C H
CH
D017362:Cyclic AMP Response Element-Binding Protein; D004247:DNA / Q000737:chemistry / Q000235:genetics; D004252:DNA Mutational Analysis; D005091:Exons / Q000235:genetics*; D005192:Family Health; D005260:Female; D006580:Genetic Carrier Screening; D006579:Heterozygote; D006801:Humans; D019656:Loss of Heterozygosity; D008297:Male; D009134:Muscular Atrophy, Spinal / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000235:genetics*; D010375:Pedigree; D016601:RNA-Binding Proteins; D055532:SMN Complex Proteins; D017384:Sequence Deletion
D017362:Cyclic AMP Response Element-Binding Protein; D009419:Nerve Tissue Proteins; D016601:RNA-Binding Proteins; D055532:SMN Complex Proteins; D004247:DNA