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Normolipidemia and hypercholesterolemia in persons heterozygous for the same 1592+5G→A splice site mutation in the low‐density lipoprotein receptor gene
Author(s) -
Jensen Hk,
Jensen Lg,
Holst Hu,
Andreasen Ph,
Hansen Ps,
Larsen Ml,
Kølvraa S,
Bolund L,
Gregersen N,
Færgeman O
Publication year - 1999
Publication title -
clinical genetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.543
H-Index - 102
eISSN - 1399-0004
pISSN - 0009-9163
DOI - 10.1034/j.1399-0004.1999.560506.x
Subject(s) - rna splicing , intron , exon , ldl receptor , microbiology and biotechnology , biology , familial hypercholesterolemia , mutant , splice site mutation , mutation , gene , splice , transfection , alternative splicing , genetics , rna , lipoprotein , endocrinology , cholesterol
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.