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

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.