A MUTATION (T-45C) IN THE PROMOTER REGION OF THE LOW-DENSITY-LIPOPROTEIN (LDL)-RECEPTOR GENE IS ASSOCIATED WITH A MILD CLINICAL PHENOTYPE IN A PATIENT WITH HETEROZYGOUS FAMILIAL HYPERCHOLESTEROLEMIA (FH)

We have identified a rare mutation (T-45C) in the low density lipoprot ein (LDL)-receptor gene in a Welsh patient with a clinical diagnosis o f heterozygous familial hypercholesterolaemia (FH). The mutation is in the proximal Sp1 binding site in repeat 3 of the 42 bp region of the promoter required for sterol-dependent regulation of transcription, bu t the substituted nucleotide is not a strongly conserved base in the c onsensus sequence for Sp1 binding. Normal and mutant promoter fragment s (from base -600 to -5) were linked to a luciferase reporter gene, an d transient expression in COS cells showed that the mutation reduced t ranscriptional activity to approximately 43% of normal in the presence , and 25% in the absence of sterols in the medium. Competitive gel-shi ft mobility assays showed that the mutation reduced the binding affini ty for transcription factor Sp1. Analysis of a neutral polymorphism in the LDL-receptor mRNA from the patient's lymphoblasts showed that exp ression of one allele was reduced. Since Southern blotting of genomic DNA and sequencing of the entire coding region of the LDL-R gene did n ot reveal any other potential defects, we infer that the T-45 C mutati on is the underlying cause of hypercholesterolaemia in the proband.