Haemophilia A resulting from de novo insertion of L1 sequences represents a novel mechanism for mutation in man

Abstract

L1 sequences are a human-specific family of long, interspersed, repetitive elements, present as approximately 10(5) copies dispersed throughout the genome. The full-length L1 sequence is 6.1 kilobases, but the majority of L1 elements are truncated at the 5' end, resulting in a fivefold higher copy number of 3' sequences. The nucleotide sequence of L1 elements includes an A-rich 3' end and two long open reading frames (orf-1 and orf-2), the second of which encodes a potential polypeptide having sequence homology with the reverse transcriptases. This structure suggests that L1 elements represent a class of non-viral retrotransposons. A number of L1 complementary DNAs, including a nearly full-length element, have been isolated from an undifferentiated teratocarcinoma cell line. We now report insertions of L1 elements into exon 14 of the factor VIII gene in two of 240 unrelated patients with haemophilia A. Both of these insertions (3.8 and 2.3 kilobases respectively) contain 3' portions of the L1 sequence, including the poly (A) tract, and create target site duplications of at least 12 and 13 nucleotides of the factor VIII gene. In addition, their 3'-trailer sequences following orf-2 are nearly identical to the consensus sequence of L1 cDNAs (ref. 6). These results indicate that certain L1 sequences in man can be dispersed, presumably by an RNA intermediate, and cause disease by insertional mutation.

Prevalence of small rearrangements in the factor VIII gene F8C among patients with severe hemophilia A

“…Such sequence alterations have been previously described for other genes coding for comparatively large protein molecules, exhibiting channel (SLC26A3 or CLD gene, involved in congenital chloride diarrhea) or receptor functions (LDL receptor gene involved in atherosclerosis) [Heath et al, 2001;Hoglund et al, 2001]. In the case of factor VIII, several gross complex rearrangements have been already reported for the gene [http://europium.csc.mrc.ac.uk ; Kazazian et al, 1988]. A very detailed description of a 316 bp deletion abolishing the acceptor splice site of exon 16 and insertion of 6 bp at the same position have been published by Tavassoli et al (1999).…”

Unusual expression of LINE-1 transposable element in the MRL autoimmune lymphoproliferative syndrome-prone strain

“…Pathogenic insertions of both non-autonomous and autonomous elements have been characterized (Kazazian, 1998) like an Alu insertion in human neurofibromatosis (Wallace et al, 1991) or an ETn insertion in murine myotonia (Steinmeyer et al, 1991). Similarly, LINE-1 insertion has been reported to suppress the expression of clotting factor VIII in a case of haemophilia (Kazazian et al, 1988) or of the dystrophin gene in Duchenne's muscular dystrophy (Holmes et al, 1994), to activate c-myc in tumours (Katzir et al, 1985;Morse et al, 1988), and to disrupt the APC gene in colorectal cancer (Miki et al, 1992).…”

Molecular analysis of an unstable genomic region at chromosome band 11q23 reveals a disruption of the gene encoding the α2 subunit of platelet-activating factor acetylhydrolase (Pafah1a2) in human lymphoma

“…This mechanism appears to play a role in some cases of gene rearrangement in somatic tissues (Strout et al, 1998). Insertion of LINE1 elements have been previously associated with human diseases, including hemophilia A and colorectal cancer, by disrupting the genes encoding factor VIII or APC, respectively (Kazazian Jr et al, 1988;Miki et al, 1992). However, since ORF1 is deleted and ORF2 is inactivated by several mis-sense mutations, the LPC line repeat does not belong to the active class of L1 recently described (Sassaman et al, 1997).…”