Abnormal apolipoprotein B pre-mRNA splicing in patients with familial hypobetalipoproteinaemia.
BACKGROUND
Familial hypobetalipoproteinaemia (FHBL) is a codominant disorder characterised by fatty liver and reduced plasma levels of low-density lipoprotein (LDL) and its protein constituent apolipoprotein B (apoB). FHBL is linked to the APOB gene in some but not all known cases. In a group of 59 patients with FHBL genotyped for APOB gene mutations, we found three novel splice-site mutations: c.904+4A-->G in intron 8, c.3843-2A-->G in intron 24 and c.4217-1G-->T in intron 25.


OBJECTIVE
To assess the effects of these mutations on apoB pre-mRNA splicing.


METHODS
ApoB mRNA was analysed in the liver of one proband and in cells expressing APOB minigenes harbouring the mutations found in the other probands.


RESULTS
In the liver of the c.3843-2A-->G carrier, an apoB mRNA devoid of exon 25 was identified, predicted to encode a truncated peptide of 1260 amino acids. The analysis of minigene transcripts in COS-1 cells showed that the c.904+4A-->G mutation caused the formation of an mRNA devoid of exon 8, predicted to encode a short apoB of 247 amino acids. The minigene harbouring the c.4217-1G-->T mutation in intron 25 generated an mRNA in which exon 25 joined to a partially deleted exon 26, resulting from the activation of an acceptor site in exon 26; this mRNA is predicted to encode a truncated protein of 1380 amino acids. All these truncated apoBs were not secreted as constituents of plasma lipoproteins.


CONCLUSIONS
These findings demonstrate the pathogenic effect of rare splice-site mutations of the APOB gene found in FHBL.
Di Leo
Enza
E
Magnolo
Lucia
L
Lancellotti
Sandra
S
Crocè
Lory
L
Visintin
Luca
L
Tiribelli
Claudio
C
Bertolini
Stefano
S
Calandra
Sebastiano
S
Tarugi
Patrizia
P
D000328:Adult; D000818:Animals; D001055:Apolipoproteins B / Q000737:chemistry / Q000172:deficiency / Q000235:genetics* / Q000502:physiology; D019556:COS Cells; D002648:Child; D002522:Chlorocebus aethiops; D004252:DNA Mutational Analysis; D005234:Fatty Liver / Q000209:etiology / Q000378:metabolism; D005260:Female; D005813:Genes, Synthetic; D005838:Genotype; D006801:Humans; D052476:Hypobetalipoproteinemia, Familial, Apolipoprotein B / Q000097:blood / Q000150:complications / Q000235:genetics*; D007438:Introns / Q000235:genetics; D008055:Lipids / Q000097:blood; D008074:Lipoproteins / Q000097:blood; D008099:Liver / Q000378:metabolism / Q000473:pathology; D008297:Male; D012322:RNA Precursors / Q000235:genetics*; D022821:RNA Splice Sites / Q000235:genetics*; D012326:RNA Splicing / Q000235:genetics; D014162:Transfection
D001055:Apolipoproteins B; D008055:Lipids; D008074:Lipoproteins; D012322:RNA Precursors; D022821:RNA Splice Sites