Normolipidemia and hypercholesterolemia in persons heterozygous for the same 1592 + 5G --> A splice site mutation in the low-density lipoprotein receptor gene.
In the present study, we have characterized a unique splice donor G to A substitution in the moderately conserved + 5 position in intron 10 of the low-density lipoprotein (LDL) receptor gene. In two Danish families, carriers of the 1592 + 5G --> A mutation display a clinical phenotype ranging from healthy normocholesterolemic persons to classical heterozygous familial hypercholesterolemia (FH) patients. Reverse transcription-polymerase chain reaction (RT-PCR) of RNA from Epstein Barr virus (EBV)-transformed lymphoblasts obtained from members of both families demonstrated abnormal splicing generating two aberrant mRNAs due to either alternative splicing and skipping of exon 10 or activation of a cryptic splice site in intron 10 inserting 66 intronic base pairs. These abnormally spliced mRNAs were predicted to encode two abnormal receptor proteins containing an in-frame deletion of 75 amino acids and an insertion of 22 novel amino acids, respectively. Results obtained by immunofluorescence staining, flow cytometry, and confocal microscopy of transfected Chang and COS-7 cells expressing normal and mutant LDL receptors were compatible with nearly complete retention of the mutant proteins in the endoplasmic reticulum. Quantitative measurements of LDL receptor mRNAs from EBV-transformed lymphoblasts, however, did not reveal any significant differences in variant mRNA contents between mutation carriers in the families that could be related to degree of hypercholesterolemia.
Jensen
H K
HK
Department of Medicine and Cardiology, Aarhus Amtssygehus University Hospital, Denmark. hkjensen@dadlnet.dk
Jensen
L G
LG
Holst
H U
HU
Andreasen
P H
PH
Hansen
P S
PS
Larsen
M L
ML
Kølvraa
S
S
Bolund
L
L
Gregersen
N
N
Faergeman
O
O
D000328:Adult; D000818:Animals; D002460:Cell Line; D004252:DNA Mutational Analysis; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006579:Heterozygote; D006801:Humans; D006938:Hyperlipoproteinemia Type II / Q000097:blood / Q000235:genetics*; D008055:Lipids / Q000097:blood*; D008297:Male; D018613:Microscopy, Confocal; D010375:Pedigree; D017354:Point Mutation; D018807:Polymorphism, Single-Stranded Conformational; D012326:RNA Splicing; D011973:Receptors, LDL / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection
D008055:Lipids; D011973:Receptors, LDL