Insertion of a 5' truncated L1 element into the 3' end of exon 44 of the dystrophin gene resulted in skipping of the exon during splicing in a case of Duchenne muscular dystrophy.

Abstract

We report here the second evidence of retrotransposition of L1, which was found inserted into the dystrophin gene of a patient, causing Duchenne muscular dystrophy (DMD). When the PCR was used to amplify a region of the dystrophin gene encompassing exon 44 from genomic DNA of two Japanese brothers with DMD, it was found to be -600 bp larger than expected. Both the normal and the abnormally large products were amplified from the DNA of their mother. However, the maternal grandparents did not have the abnormal allele, and the mutation must therefore have occurred in the mother. Analysis of nucleotide sequence of the amplified product from a patient disclosed that the insertion was present zero to two bases upstream from the 3' end of exon 44 and that two to four bases of the exon sequence were deleted from the insertion site. The insertion sequence was found to be composed of 606-608 bp and to be almost identical to the inverse complement of 3' portion of the Li retrotransposon consensus sequence. The dystrophin gene transcript from peripheral lymphocytes of one of the patients was analyzed by using reverse transcription/ semi-nested PCR. The size of the amplified product encompassing exon 42 to 46 was smaller than expected. Sequencing of the amplified product disclosed that the sequence of exon 43 was directly joined to that of exon 45. Exon 44 of the transcript was thus shown to be skipped during splicing. This novel mutation of the dystrophin gene has important implications regarding retrotransposition of an active Ll element and provides a new insight into the origins of mutations in the dystrophin gene. (J.

Mutation spectrum of the dystrophin gene in 442 Duchenne/Becker muscular dystrophy cases from one Japanese referral center

“…43 In our series, two retrotransposon insertions were found. 34 Their identification was because of the elongation of exon size, which made PCR amplification difficult, and could have resulted in misdiagnosis as a single-exon deletion. Therefore, we propose that supposed single-exon deletion cases should be examined in more detail.…”

“…Two insertions, which were 606 bp within exon 44 and 325 bp within exon 67, respectively, were found to be identical in DNA sequence to retrotransposons. 34 In one BMD case a splicing error was detected, although there was no mutation in the gDNA (KUCG no. 338 in Table 4).…”

L1 retrotransposition in nondividing and primary human somatic cells

“…To date, L1 retrotransposition has been detected only in germ cells (16,(28)(29)(30)(31)(32), transformed or immortalized cells (13,(33)(34)(35), and, most recently, in select rodent somatic cells (16), and it remained unclear whether cell division is required for L1 retrotransposition. Unfortunately, the inability to efficiently introduce engineered RC-L1s expressed from EBNA͞ori P-based plasmids into quiescent cells has made it difficult to answer this question unambiguously.…”

A transcription map of the minimally deleted region from 13q14 in B-cell chronic lymphocytic leukemia as defined by large scale sequencing of the 650 kb critical region

“…Genscan-predicted gene #6 shares homology with the ®rst ORF of the L1 element, and Genscan-predicted gene #9 shares homology with the second ORF of the L1 element. There are several reports in the literature describing the involvement of L1 element transpositions in genetic diseases, including human breast carcinoma and colon cancer (Kazazian et al, 1988;Morse et al, 1988;Miki et al, 1992;Narita et al, 1993;Holmes et al, 1994). It is more likely, however, Transcript map of B-CLL deletion E Kitamura et al that the L1 element predicted in the 312 kb contig is functionally inactive for several reasons.…”