Mutation -59c-->t in repeat 2 of the LDL receptor promoter: reduction in transcriptional activity and possible allelic interaction in a south african family with familial hypercholesterolaemia

Abstract

The low-density lipoprotein receptor (LDLR) plays a major role in cholesterol homeostasis. Mutations in the regulatory region of the LDLR gene, although rare, have been shown to alter transcriptional activity of the gene and can cause familial hypercholesterolaemia (FH). In this study, a transition (c-->t) was identified at nucleotide position -59 within repeat 2 of the LDLR promoter in a South African FH patient of mixed ancestry. By screening 17 family members of the index case for this promoter mutation, two additional single base changes (-124c-->t and-175g-->t) were identified, located at recently described cis- acting regulatory sequences of the LDLR promoter. Both the-59c-->t and the-124c-->t transitions were identified in the normocholesterolaemic son of the index patient. Reporter plasmids containing the normal and mutant promoter fragments were constructed by directional cloning. Transcription studies using a luciferase reporter system demonstrated that the-59c-->t mutation significantly reduces promoter activity in both the presence and absence of sterols ( approximately 40% of normal activity), while the-124c-->t variant increases transcription ( approximately 160%) of the LDLR gene. The intra-familial phenotypic variability observed amongst individuals with the-59c-->t mutation can probably be ascribed to allelic interaction, suggesting that variation in the LDLR promoter region may contribute significantly to the phenotypic expression of FH-related mutations in populations where these mutations prevail.

Update and Analysis of the University College London Low Density Lipoprotein Receptor Familial Hypercholesterolemia Database

“…Variants that fall outside the regulatory elements also altered expression (Fig. 4b, c.− 217C >T & c.− 120C >T); however, c.− 268G >T which lies in FP2 has been reported as a non-FH variant present at polymorphic frequency in African subjects (Scholtz et al 1999). The finding that variants in the LDLR promoter region can reduce, elevate or have little effect on transcription, irrespective of whether or not the variant lies within one of the regulatory elements, emphasises the importance of in vitro expression studies for these variants.…”

“…In vitro expression reports were available for 8 variants (Fig. 4b); of these, 7 resulted in reduced expression from the LDLR promoter, whilst the variant c.− 217C >T (2bp away from 3 end of FP1), elevated expression to 160% of normal (Scholtz et al 1999). Variants that fall outside the regulatory elements also altered expression (Fig.…”

LDLR promoter variant and exon 14 mutation on the same chromosome are associated with an unusually severe FH phenotype and treatment resistance

“…Full-gene sequencing for LDLR uncovered two point variants (Table 1): a novel exon 14 mutation (2041T4G; Cys681Gly) and a promoter region variant (IVS1-217C4T) that has previously been linked to increased transcription of LDLR. 10 Gene dosage analysis of LDLR by multiplex ligation-dependent probe amplification did not reveal any large rearrangements in the gene. Similarly, the patient was negative for the two most common disease-causing mutations in APOB.…”

“…The IVS1-217C4T promoter variant has been shown in vitro to increase LDLR transcription to B160% of normal. 10 Because the promoter variant is in cis with the exon 14 mutation, there would be an expected increase in expression of the mutant Cys681Gly allele. Thus, enhanced transcription of the mutated receptor likely shifts the balance of expression to favor that of the mutant LDLR gene relative to the wild type, resulting in a gene-dosage effect leading to a unique phenotype that has features of both classic heterozygous and classic homozygous FH.…”

Analysis of polymorphisms in the 3' untranslated region of the LDL receptor gene and their effect on plasma cholesterol levels and drug response

“…Mutations in different coding regions of the LDLR gene reduce receptor activity and give rise to the clinical phenotype of heterozygous familial hypercholesterolemia that is characterized by increased plasma levels of total cholesterol (TC) and LDL-c, tendinous xanthomata, and premature CHD (1)(2)(3). In addition to mutations in coding regions, mutations in the 5' promoter regions of the LDLR gene have been identified in hypercholesterolemic patients (4)(5)(6)(7). These mutations compromise promoter activity and reduce LDLR expression (6,8).…”