A new Italian case of lipoprotein lipase deficiency: a Leu365- > Val change resulting in loss of enzyme activity

Pathogenic classification of LPL gene variants reported to be associated with LPL deficiency

BACKGROUND

Lipoprotein lipase (LPL) deficiency is a serious lipid disorder of severe hypertriglyceridemia (SHTG) with chylomicronemia. A large number of variants in the LPL gene have been reported but their influence on LPL activity and SHTG has not been completely analyzed. Gaining insight into the deleterious effect of the mutations is clinically essential.

METHODS

We used gene sequencing followed by in-vivo/in-vitro and in-silico tools for classification. We classified 125 rare LPL mutations in 33 subjects thought to have LPL deficiency and in 314 subjects selected for very SHTG.

RESULTS

Of the 33 patients thought to have LPL deficiency, only 13 were homozygous or compound heterozygous for deleterious mutations in the LPL gene. Among the 314 very SHTG patients, 3 were compound heterozygous for pathogenic mutants. In a third group of 51,467 subjects, from a general population, carriers of common variants, Asp9Asn and Asn291Ser, were associated with mild increase in triglyceride levels (11%-35%).

CONCLUSION

In total, 39% of patients clinically diagnosed as LPL deficient had 2 deleterious variants. Three patients selected for very SHTG had LPL deficiency. The deleterious mutations associated with LPL deficiency will assist in the diagnosis and selection of patients as candidates for the presently approved LPL gene therapy.

Identification of genetic variants in endothelial lipase in persons with elevated high-density lipoprotein cholesterol

BACKGROUND

Elevated high-density lipoprotein cholesterol (HDL-C) is associated with reduced risk of cardiovascular disease, and variation in HDL-C levels has been shown to be approximately 50% heritable. Overexpression of endothelial lipase (EL), a member of the lipoprotein lipase gene family, markedly reduces HDL-C levels in mouse models. We hypothesized that genetic variation in EL might be associated with elevated HDL-C.

METHODS AND RESULTS

All exons and 1.2 kilobase of promoter of the EL gene were sequenced in 20 unrelated human subjects with high HDL-C levels. A total of 17 variants were identified. Six of these were potentially functional and were confirmed by restriction enzyme analysis. Four variants result in amino acid changes (Gly26Ser, Thr111Ile, Thr298Ser, and Asn396Ser,) and 2 variants were in the promoter (-303A/C and -410C/G). The genotype frequencies of each variant were determined in 176 black controls, 165 white controls, and 123 whites with high HDL-C. The Thr111Ile variant was the most common, with an allele frequency of 10.3% in blacks, 31.2% in white controls, and 32.6% in the high HDL-C group. The remaining variants all had allele frequencies <5.0% but differed in frequency among the 3 groups. Interestingly, Gly26Ser, Thr298Ser, and -303A/C were found in the black and high HDL-C white cohorts but were absent in the control white group.

CONCLUSIONS

Six new potentially functional variants in EL were discovered through sequencing of the EL gene in subjects with high HDL-C levels. Differences in allele frequencies exist between blacks and whites and between control subjects and those with high HDL-C levels.

Lipoprotein lipase (LPL) deficiency: a new patient homozygote for the preponderant mutation Gly188Glu in the human LPL gene and review of reported mutations: 75 % are clustered in exons 5 and 6

We have investigated the lipoprotein lipase (LPL) gene of a 2-year-old patient presenting classical features of the familial LPL deficiency including undetectable LPL activity. DNA sequence analysis of exon 5 identified the patient as a homozygote for the Gly188Glu mutation, frequently involved in this disease. A review of cases of LPL deficiency with molecular study of the LPL gene showed a total number of 221 reported mutations involved in this disease. Gly188Glu was involved in 23.5 % of cases and 74.6 % of mutations were clustered in exons 5 and 6. Based on these observations, we propose a method of screening for mutations in this gene.

Molecular pathobiology of the human lipoprotein lipase gene

Lipoprotein lipase (LPL; E.C. 3.1.1.34) is a key enzyme in the metabolism of lipids. Many diseases, including obesity, coronary heart disease, chylomicronemia (pancreatitis), and atherosclerosis, appear to be directly or indirectly related to abnormalities in LPL function. Human LPL is a member of a superfamily of lipases that includes hepatic lipase and pancreatic lipase. These lipases are characterized by extensive homology, both at the level of the gene and the mature protein, suggesting that they have a common evolutionary origin. A large number of natural mutations have been discovered in the human LPL gene, which are located at different sites in the gene and affect different functions of the mature protein. There is a high prevalence of two of these mutations (207 and 188) in the Province of Québec, and one of them (207) is almost exclusive to the French-Canadian population. A study of these and other naturally occurring mutant LPL molecules, as well as those created in vitro by site-directed mutagenesis, indicate that the sequence of LPL is organized into multiple structural and functional units that act in concert in the normal enzyme. In this review, we discuss the interrelationships of LPL structure and its function, the molecular etiology of abnormal LPL in humans, and the clinical and therapeutic aspects of LPL deficiency.