Screening for point mutations in the LDL receptor gene in Bulgarian patients with severe hypercholesterolemia

Abstract

Familial hypercholesterolemia (FH) is a common, autosomal dominant disorder of lipid metabolism, caused by defects in the receptor-mediated uptake of LDL (low-density lipoproteins) due to mutations in the LDL receptor gene (LDLR). Mutations underlying FH in Bulgaria are largely unknown. The aim of the present study was to provide information about the spectrum of point mutations in LDLR in a sample of 45 Bulgarian patients with severe hypercholesterolemia. Exons 3, 4, 6, 8, 9, and 14, previously shown to be mutational hot spots in LDLR, were screened using PCR-single-strand conformation polymorphism (SSCP). Samples with abnormal SSCP patterns were sequenced. Three different, hitherto undescribed point mutations (367T>A, 377T>A, 917C>A) and two previously described mutations (858C>A and 1301C>T) in eight unrelated patients were identified; four of the detected point mutations being missense mutations and one, a nonsense mutation. One of the newly described point mutations (917C>A) is a base substitution at a nucleotide position, at which two other different base substitutions have already been reported. Thus, all three possible base substitutions at this nucleotide position have been detected, making it a hot spot for point mutations causing FH. This is the first such mutational hot spot described in exon 6 of LDLR.

Increased Intima-Media Thickness in Carriers of the LDL-Receptor Defective Gene versus Noncarriers with Newly Detected Asymptomatic Severe Hypercholesterolemia

“…Using a study protocol as recommended by previous studies on establishing mutations in LDL-R gene, we found 18% carriers of molecular defect. 6 This result is close to what we expected based on data in previous studies (13-40% in severe hypercholesterolemia). The current results are nearer the lower limit of the range because the patients were examined only for spot mutations and polymorphisms of LDL-R but not for major rearrangements.…”

“…[3][4][5] The incidence of spot mutations established in this study is lower than that reported by Ganev et al in patients with moderate to severe hypercholesterolemia (18%). 3,5,6 This may be accounted for by the fact that this finding was established only in patients with severe hypercholesterolemia (>8.5 mmol/L) whereas our study included hypercholesterolemic patients with total cholesterol above 7.5 mmol/L.…”

“…The current results are nearer the lower limit of the range because the patients were examined only for spot mutations and polymorphisms of LDL-R but not for major rearrangements. 4,6,7 The analysis of the distribution of some of protein domains-affecting mutations shows that 3 are located in the ligandconnecting domain (4b, 5, 6) and 10 in the epithelial growth factor precursor-homology domain. Literature data give 42% and 47% of all mutations to be located in those two domains of the LDL-R gene.…”

“…It is known that routine lipid parameters are little informative with respect to identifying carriers or noncarriers of LDL-R defects. [3][4][5][6] Severe hypercholesterolemia and family history of early vascular diseases are important determinants of the development of the intima-media complex of the common carotid artery (IMT CCA) and flow-mediated vasodilation (%FMD) in FH. [7][8][9][10][11][12] The data on the examination of early vascular alterations (functionalusing %FMD, and structural-by measurement of the IMT CCA in carriers of molecular defects of the LDL-R in comparison to noncarriers with severe hypercholesterolemia in the literature are controversial.…”

“…[12][13][14][15][16][17][18][19] Evidence on this issue could be used in developing the treatment algorithm of newly detected severe hypercholesterolemia. Most of the studies on severe FH are carried out in patients with manifested coronary artery disease, [3][4][5][6] data about patients with asymptomatic FH are scarce.…”