[Comparison and analysis of the molecular character of breakpoints in introns of deletion hotspots of dystrophin gene].
OBJECTIVE
To study the exons deletion mechanisms for dystrophin gene, the molecular characters of breakpoints of junction fragments for deletion-type Duchenne muscular dystrophy (DMD) patients with 46 and 51 exons deletion were compared and analyzed.


METHODS
Deletion-type DMD patients were detected by multiplex polymerase chain reaction(mPCR). The breakpoints of junction fragments with 46 and 51 exons deletions were cloned and sequenced respectively.


RESULTS
Analysis of sequences of deletion-junction fragment of exon 46 showed that the 5'breakpoint was located in AT-rich region of intron 45 and the 3' breakpoint was in medium reiteration repeats (MER1) sequence. There existed 2 bp(ta) junction homology between two breakages. No small insertion, small deletion or point mutation was located near the junction point. Similarly, analysis of sequences of deletion-junction fragment of exon 51 showed that the 5   breakpoint was located in transposon-like human elements (THE1) of intron 50 and the 3' breakpoint was in L2 sequence. There existed 3 bp(cta) junction homology between two breakages. No small insertion, small deletion or point mutation was located near the junction point. By analyzing the secondary structure of junction fragments with 46 and 51 exons deletions, it was demonstrated that all breakpoints of junction fragments were located at the non-matching regions of single-strand hairpin.


CONCLUSIONS
By comparing the junction fragments with 46 or 51 exons deletion, it was found that all of breakpoints were located in repeat sequences and the repeat sequences formed the single-strand hairpin which could make the introns instable and result in exon deletion.
Sheng
Wen-li
WL
Department of Neurology, the First Affiliated Hospital, Sun Yat-sen University, Guangzhou, Guangdong,510080 PR China. wenlisheng@hotmail.com
Chen
Jiang-ying
JY
Pan
Su-yue
SY
Zhang
Cheng
C
Liu
Zhuo-lin
ZL
D001483:Base Sequence; D004247:DNA / Q000737:chemistry / Q000235:genetics; D004252:DNA Mutational Analysis; D016189:Dystrophin / Q000235:genetics*; D005091:Exons / Q000235:genetics; D007438:Introns / Q000235:genetics*; D008969:Molecular Sequence Data; D020388:Muscular Dystrophy, Duchenne / Q000235:genetics*; D009690:Nucleic Acid Conformation; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics; D017384:Sequence Deletion
D016189:Dystrophin; D004247:DNA