Eight novel mutations and functional impairments of the LDL receptor in familial hypercholesterolemia in the north of Japan

In the course of investigations of familial coronary artery disease in Hokkaido, the northland of Japan, we identified 13 families affected by familial hypercholesterolemia. Among them, we identified eight novel mutations of the low-density lipoprotein (LDL) receptor gene, four of which caused frameshifts: (1) a 7-bp deletion at nucleotide (nt) 578-584 (codon 172-174, exon 4); (2) a 14-bp insertion at 682nt (codon 207-208, exon 4); (3) a 49-bp deletion at nt 943-991 (codon 294-310, exon 7); and (4) a one-base insertion of C to a stretch of C3 at nucleotides 1687-1689 or codon 542. The others included (5) a T-to-C transition at nt 1072 causing substitution of Cys for Arg at codon 337 (C337R, exon 8); (6) a splice-site G-to-T substitution in intron 11; (7) a splice-site G-to-C substitution in intron 11; and (8) a G-to-T transition at nt 1731 causing substitution of Trp for Cys at codon 556 (W556C, exon 12). To disclose the functional consequences of novel mutations, we characterized each of these mutations by two assays in peripheral lymphocytes, i.e., uptake of fluorescently labeled LDL by LDL receptors, and measurement of cell surface-bound LDL receptor protein using specific monoclonal antibody against LDL receptor.