Primary hyperlipidemia is caused by various molecular defects in lipid metabolism. The Research Committee on Primary Hyperlipidemia organized by the Ministry of Health and Welfare of Japan (present: the Ministry of Health, Labour and Welfare) has investigated reported mutations in Japanese patients with primary hyperlipidemia and related disorders (including hypolipidemia), and has created a database based on the questionnaire sent to the members of council board of the Japan Atherosclerosis Society. Mutations in the following genes were investigated: low density lipoprotein receptor, lecithin: cholesteryl acyltransferase, lipoprotein lipase (LPL), hepatic lipase, apolipoproteins A-I, A-II, A-IV, B, C-II, C-III and E, microsomal triglyceride transfer protein, and cholesterol ester transfer protein (CETP). Until 1998, 922 patients with primary hyperlipidemia and related disorders has been registered with the Research Committee, and 190 mutations in 15 genes had been reported, showing a marked variation in Japanese patients with primary hyperlipidemia and related disorders. So-called "common mutations" have been described in Japanese patients with familial hypercholesterolemia, LPL deficiency and CETP deficiency. The genetic defect of familial combined hyperlipidemia (FCHL) is still unknown although FCHL is speculated to be the most prevalent genetic hyperlipidemia, and further investigations should be performed to elucidate the molecular mechanisms of FCHL
        
Title: A newly identified lipoprotein lipase (LPL) gene mutation (F270L) in a Japanese patient with familial LPL deficiency Takagi A, Ikeda Y, Takeda E, Yamamoto A Ref: Biochimica & Biophysica Acta, 1502:433, 2000 : PubMed
We have systematically investigated the molecular defects resulting in a primary lipoprotein lipase (LPL) deficiency in a Japanese male infant (proband SH) with fasting hyperchylomicronemia. Neither LPL activity nor immunoreactive LPL mass was detected in pre- or postheparin plasma from proband SH. DNA sequence analysis of the LPL gene of proband SH revealed homozygosity for a novel missense mutation of F270L (Phe(270)-->Leu/TTT(1065)-->TTG) in exon 6. The function of the mutant F270L LPL was determined by both biochemical and immunocytochemical studies. In vitro expression experiments on the mutant F270L LPL cDNA in COS-1 cells demonstrated that the mutant LPL protein was synthesized as a catalytically inactive form and its total amount was almost equal to that of the normal LPL. Moreover, the synthesized mutant LPL was non-releasable by heparin because the intracellular transport of the mutant LPL to the cell surface - by which normal LPL becomes heparin-releasable - was impaired due to the abnormal structure of the mutant LPL protein. These findings explain the failure to detect LPL activities and masses in pre- and postheparin plasma of the proband. The mutant F270L allele generated an XcmI restriction enzyme site in exon 6 of the LPL gene. The carrier status of F270L in the proband's family members was examined by digestion with XcmI. The proband was ascertained to be homozygous for the F270L mutation and his parents and sister were all heterozygous. The LPL activities and masses of the parents and the sister (carriers) were half or less than half of the control values. Regarding the phenotype of the carriers, the mother with a sign of hyperinsulinemia manifested hypertriglyceridemia (type IV hyperlipoproteinemia), whereas the healthy father and the sister were normolipidemic. Hyperinsulinemia may be a strong determinant of hypertriglyceridemia in subjects with heterozygous LPL deficiency.