[Detection of homozygous deletions in spinal muscular atrophy with genomic DNA sequencing].
OBJECTIVE
To detect homozygous deletions of survival motor neuron (SMN) gene with genomic DNA sequencing, and to assess the value of genetic testing for the diagnosis of spinal muscular atrophy (SMA).


METHODS
Polymerase chain reaction (PCR) was used for amplifying SMN gene in 100 SMA patients and 110 controls. Four different bases (g.31957, g.32006, g.32154 and g.32269) between SMN1 and SMN2 within the amplified segments were identified with genomic DNA sequencing. Homozygous deletion of SMN1 or SMN2 was determined by the presence or absence of base peaks at such four sites. Multiplex ligation-dependent probe amplification (MLPA) was carried out to confirm the results of genomic DNA sequencing.


RESULTS
In the 100 SMA samples, only SMN2 specific base peaks were detected at the four sites, for which the copy numbers of SMN1 and SMN2 was 0:2 or 0:3, suggesting homozygous deletion of SMN1 gene. By contrast, only SMN1 specific base peaks were detected in 5 samples, for which the ratio of SMN1:SMN2 was 2:0, indicating homozygous deletion of SMN2. At four different sites, SMN1/SMN2 heterozygous peaks were detected in the remaining 105 samples, for which SMN1:SMN2was 2:2, suggesting non-deletion of SMN1 or SMN2. The results of sequencing were consistent with those of MLPA.


CONCLUSIONS
Genomic DNA sequencing is a rapid, accurate and economic method for the diagnosis of homozygous deletion of SMA.
Department of Medical Genetics, Capital Institute of Pediatrics, Beijing 100020, P. R. China. songf_558@263.net.
Yan-yan
YY
Cao
Yu-jin
YJ
Qu
Fang
F
Song
Jin-li
JL
Bai
Yu-wei
YW
Jin
Hong
H
Wang
Yan
Y
Li
Wen-hui
WH
Zhang
D001483:Base Sequence; D002681:China; D005260:Female; D005838:Genotype; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D009134:Muscular Atrophy, Spinal / Q000235:genetics*; D017422:Sequence Analysis, DNA; D017384:Sequence Deletion; D055533:Survival of Motor Neuron 1 Protein / Q000235:genetics; D055540:Survival of Motor Neuron 2 Protein / Q000235:genetics
C526471:SMN1 protein, human; C526477:SMN2 protein, human; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein