Deficiency of lecithin:cholesterol acyltransferase due to compound heterozygosity of two novel mutations (Gly33Arg and 30 bp ins) in the LCAT gene

A systematic review of the natural history and biomarkers of primary lecithin:cholesterol acyltransferase deficiency

Syndromes associated with LCAT deficiency, a rare autosomal recessive condition, include fish-eye disease (FED) and familial LCAT deficiency (FLD). FLD is more severe and characterized by early and progressive chronic kidney disease (CKD). No treatment is currently available for FLD, but novel therapeutics are under development. Furthermore, although biomarkers of LCAT deficiency have been identified, their suitability to monitor disease progression and therapeutic efficacy is unclear, as little data exist on the rate of progression of renal disease. Here, we systematically review observational studies of FLD, FED, and heterozygous subjects, which summarize available evidence on the natural history and biomarkers of LCAT deficiency, in order to guide the development of novel therapeutics. We identified 146 FLD and 53 FED patients from 219 publications, showing that both syndromes are characterized by early corneal opacity and markedly reduced HDL-C levels. Proteinuria/hematuria were the first signs of renal impairment in FLD, followed by rapid decline of renal function. Furthermore, LCAT activity toward endogenous substrates and the percentage of circulating esterified cholesterol (EC%) were the best discriminators between these two syndromes. In FLD, higher levels of total, non-HDL, and unesterified cholesterol were associated with severe CKD. We reveal a nonlinear association between LCAT activity and EC% levels, in which subnormal levels of LCAT activity were associated with normal EC%. This review provides the first step toward the identification of disease biomarkers to be used in clinical trials and suggests that restoring LCAT activity to subnormal levels may be sufficient to prevent renal disease progression.

LCAT deficiency: a systematic review with the clinical and genetic description of Mexican kindred

BACKGROUND

LCAT (lecithin-cholesterol acyltransferase) deficiency is characterized by two distinct phenotypes, familial LCAT deficiency (FLD) and Fish Eye disease (FED). This is the first systematic review evaluating the ethnic distribution of LCAT deficiency, with particular emphasis on Latin America and the discussion of three Mexican-Mestizo probands.

METHODS

A systematic review was conducted following the PRISMA (Preferred Reporting Items for Systematic review and Meta-Analysis) Statement in Pubmed and SciELO. Articles which described subjects with LCAT deficiency syndromes and an assessment of the ethnic group to which the subject pertained, were included.

RESULTS

The systematic review revealed 215 cases (154 FLD, 41 FED and 20 unclassified) pertaining to 33 ethnic/racial groups. There was no association between genetic alteration and ethnicity. The mean age of diagnosis was 42 ± 16.5 years, with fish eye disease identified later than familial LCAT deficiency (55 ± 13.8 vs. 41 ± 14.7 years respectively). The prevalence of premature coronary heart disease was significantly greater in FED vs. FLD. In Latin America, 48 cases of LCAT deficiency have been published from six countries (Argentina (1 unclassified), Brazil (38 FLD), Chile (1 FLD), Columbia (1 FLD), Ecuador (1 FLD) and Mexico (4 FLD, 1 FED and 1 unclassified). Of the Mexican probands, one showed a novel LCAT mutation.

CONCLUSIONS

The systematic review shows that LCAT deficiency syndromes are clinically and genetically heterogeneous. No association was confirmed between ethnicity and LCAT mutation. There was a significantly greater risk of premature coronary artery disease in fish eye disease compared to familial LCAT deficiency. In FLD, the emphasis should be in preventing both cardiovascular disease and the progression of renal disease, while in FED, cardiovascular risk management should be the priority. The LCAT mutations discussed in this article are the only ones reported in the Mexican- Amerindian population.

Lecithin: cholesterol acyltransferase--from biochemistry to role in cardiovascular disease

PURPOSE OF REVIEW

We discuss the latest findings on the biochemistry of lecithin : cholesterol acyltransferase (LCAT), the effect of LCAT on atherosclerosis, clinical features of LCAT deficiency, and the impact of LCAT on cardiovascular disease from human studies.

RECENT FINDINGS

Although there has been much recent progress in the biochemistry of LCAT and its effect on high-density lipoprotein metabolism, its role in the pathogenesis of atherosclerosis is still not fully understood. Studies from various animal models have revealed a complex interaction between LCAT and atherosclerosis that may be modified by diet and by other proteins that modify lipoproteins. Furthermore, the ability of LCAT to lower apoB appears to be the best way to predict its effect on atherosclerosis in animal models. Recent studies on patients with LCAT deficiency have shown a modest but significant increase in incidence of cardiovascular disease consistent with a beneficial effect of LCAT on atherosclerosis. The role of LCAT in the general population, however, has not revealed a consistent association with cardiovascular disease.

SUMMARY

Recent research findings from animal and human studies have revealed a potential beneficial role of LCAT in reducing atherosclerosis but additional studies are necessary to better establish the linkage between LCAT and cardiovascular disease.

High density lipoproteins (HDLs) and atherosclerosis; the unanswered questions

The concentration of high density lipoprotein-cholesterol (HDL-C) has been found consistently to be a powerful negative predictor of premature coronary heart disease (CHD) in human prospective population studies. There is also circumstantial evidence from human intervention studies and direct evidence from animal intervention studies that HDLs protect against the development of atherosclerosis. HDLs have several documented functions, although the precise mechanism by which they prevent atherosclerosis remains uncertain. Nor is it known whether the cardioprotective properties of HDL are specific to one or more of the many HDL subpopulations that comprise the HDL fraction in human plasma. Several lifestyle and pharmacological interventions have the capacity to raise the level of HDL-C, although it is not known whether all are equally protective. Indeed, despite the large body of information identifying HDLs as potential therapeutic targets for the prevention of atherosclerosis, there remain many unanswered questions that must be addressed as a matter of urgency before embarking wholesale on HDL-C-raising therapies as strategies to prevent CHD. This review summarises what is known and highlights what we still need to know.

Lecithin:cholesterol acyl transferase G30S: association with atherosclerosis, hypoalphalipoproteinemia and reduced in vivo enzyme activity

OBJECTIVES

A 69 yr old male was referred for assessment of a very low plasma HDL cholesterol and apolipoprotein AI concentration. At age 65, he had undergone triple vessel coronary bypass graft surgery. He had a strong family history of early coronary heart disease. We analyzed the molecular basis of his clinical and biochemical abnormalities.

DESIGN AND METHODS

We used DNA sequencing to determine whether mutations in LCAT were present. We also evaluated plasma biochemistry and LCAT activity.

RESULTS

DNA sequencing revealed that the patient was a heterozygote for the G30S mutation in the gene encoding lecithin:cholesteol acyl transferase (LCAT). His plasma was found to have half-normal LCAT activity.

CONCLUSIONS

The findings in this patient suggest that rare dysfunctional mutations in candidate genes, such as LCAT, can contribute to the spectrum of patients ascertained because of low HDL cholesterol.

Analysis of glomerulosclerosis and atherosclerosis in lecithin cholesterol acyltransferase-deficient mice

To evaluate the biochemical and molecular mechanisms leading to glomerulosclerosis and the variable development of atherosclerosis in patients with familial lecithin cholesterol acyl transferase (LCAT) deficiency, we generated LCAT knockout (KO) mice and cross-bred them with apolipoprotein (apo) E KO, low density lipoprotein receptor (LDLr) KO, and cholesteryl ester transfer protein transgenic mice. LCAT-KO mice had normochromic normocytic anemia with increased reticulocyte and target cell counts as well as decreased red blood cell osmotic fragility. A subset of LCAT-KO mice accumulated lipoprotein X and developed proteinuria and glomerulosclerosis characterized by mesangial cell proliferation, sclerosis, lipid accumulation, and deposition of electron dense material throughout the glomeruli. LCAT deficiency reduced the plasma high density lipoprotein (HDL) cholesterol (-70 to -94%) and non-HDL cholesterol (-48 to -85%) levels in control, apoE-KO, LDLr-KO, and cholesteryl ester transfer protein-Tg mice. Transcriptome and Western blot analysis demonstrated up-regulation of hepatic LDLr and apoE expression in LCAT-KO mice. Despite decreased HDL, aortic atherosclerosis was significantly reduced (-35% to -99%) in all mouse models with LCAT deficiency. Our studies indicate (i) that the plasma levels of apoB containing lipoproteins rather than HDL may determine the atherogenic risk of patients with hypoalphalipoproteinemia due to LCAT deficiency and (ii) a potential etiological role for lipoproteins X in the development of glomerulosclerosis in LCAT deficiency. The availability of LCAT-KO mice characterized by lipid, hematologic, and renal abnormalities similar to familial LCAT deficiency patients will permit future evaluation of LCAT gene transfer as a possible treatment for glomerulosclerosis in LCAT-deficient states.

High-density lipoprotein: gene-based approaches to the prevention of atherosclerosis

Although the atheroprotective role of high-density lipoprotein (HDL) has been well documented in epidemiological and animal studies, highly effective therapeutic approaches for the selective increase of plasma HDL levels or function are not yet available. Several mechanisms by which HDL exerts an atheroprotective effect have been proposed on the basis of experiments in vitro and in vivo. These mechanisms include directing excess cellular cholesterol from the peripheral tissues to the liver in 'reverse cholesterol transport', inhibiting oxidative modification or aggregation of LDL, and modulating inflammatory responses to favour vasoprotection. This review gives an overview of the genes regulating these mechanisms, such as those encoding apolipoprotein AI, lecithin:cholesterol acyltransferase (LCAT), scavenger receptor B1 (SR-BI), and the ATP-binding cassette transporter 1 (ABC1), and the potential to exploit them to develop gene-based therapeutic approaches to increase the level or function of HDL.

Lecithin-cholesterol acyltransferase: role in lipoprotein metabolism, reverse cholesterol transport and atherosclerosis

In the past several years significant advances have been made in our understanding of lecithin-cholesterol acyltransferase (LCAT) function. LCAT beneficially alters the plasma concentrations of apolipoprotein B-containing lipoproteins, as well as HDL. In addition, its proposed role in facilitating reverse cholesterol transport and modulating atherosclerosis has been demonstrated in vivo. Analysis of LCAT transgenic animals has established the importance of evaluating HDL function, as well as HDL plasma levels, to predict atherogenic risk.

Classical LCAT deficiency resulting from a novel homozygous dinucleotide deletion in exon 4 of the human lecithin: cholesterol acyltransferase gene causing a frameshift and stop codon at residue 144

Lecithin: cholesterolacyltransferase (LCAT) transacylates the fatty acid at the sn-2 position of lecithin to the 3beta-OH group of cholesterol forming lysolecithin and the majority of cholesteryl ester found in plasma. LCAT participates in the reverse cholesterol transport pathway in man where it esterifies tissue-derived cholesterol following efflux from peripheral cells into HDL. Only 38 unique mutations in the human LCAT gene have been reported worldwide. Our French female proband presented with corneal opacity and no detectable plasma LCAT activity using either endogenous or exogenous assays. Her total plasma cholesterol and HDL cholesterol were low (2.34 mmol/l and 0.184 mmol/l, respectively) with a very high cholesterol/cholesteryl ester molar ratio (10.9:1). Plasma triglycerides were 0.470 mmol/l with low apo B (40.5 mg/dl), apo A-I (14.7 mg/dl), apo A-II (6.8 mg/dl) and apo E (2.1 mg/dl) levels. Plasma lipoprotein analysis by ultracentrifugation showed very low HDL concentrations and a characteristic shift of the lipoprotein profile towards larger, less dense particles. No proteinuria, renal dysfunction or signs of atherosclerosis were noted at age 45. Sequence analysis of her LCAT gene showed a novel homozygous TG-deletion at residues 138-139 that resulted in a frameshift causing the generation of a stop codon and premature termination of the LCAT protein at amino acid residue 144. Western blotting of the patient's plasma using a polyclonal IgY primary antibody against human LCAT failed to demonstrate the presence of a truncated LCAT protein. A 53 bp mismatched PCR primer was designed to generate an Fsp 1 restriction site in the wild type sequence of exon 4 where the mutation occurred. The 155 bp PCR product from the wild type allele produced a 103 bp and 52 bp fragment with Fsp 1 and no cleavage products with the mutant allele thus permitting rapid screening for this novel mutation.

Remodelling of high density lipoproteins by plasma factors

Evidence that the high density lipoproteins (HDL) in human plasma are antiatherogenic has stimulated considerable interest in the factors which regulate their structure and function. Plasma HDL consist of a number of subpopulations of particles of varying size, density and composition. This structural heterogeneity is caused by the continual remodelling of individual HDL subpopulations by various plasma factors. One of the consequences of this remodelling is that the HDL subpopulations in plasma are functionally diverse, particularly in terms of their antiatherogenic properties. This review documents what is currently known about the interaction of HDL with plasma factors and presents an overview of the remodelling of HDL which occurs as a consequence of those interactions.

Familial lecithin:cholesterol acyltransferase deficiency: molecular analysis of a compound heterozygote: LCAT (Arg147 --> Trp) and LCAT (Tyr171 --> Stop)

Lecithin:cholesterol acyltransferase (LCAT) is responsible for the formation of the majority of plasma cholesteryl esters. Familial LCAT deficiency is associated with corneal opacity, anemia and proteinurea and typically results in renal failure in the 4-5th decade; this syndrome is equally characterized by the quasi-absence of plasma LCAT activity with variable enzyme mass and very low levels of plasma cholesteryl esters. In this study, we report detailed analyses of plasma lipids and lipoprotein profile in two sisters (CM and ML) presenting classical homozygous LCAT-deficiency; the younger sibling (CM) had proteinurea from an early age whereas the older sister (ML) has never exhibited renal dysfunction. We investigated the molecular defect in the 45 year-old woman (proband CM) exhibiting all clinical and biochemical features of familial LCAT deficiency: a plasma cholesterol level of 105 mg/dl, of which 95% was unesterified, an HDL-cholesterol of 6.5 mg/dl and an apo A-I level of 52 mg/dl. The proband (CM) displayed a plasma cholesterol esterification rate which corresponded to 2% of normal LCAT activity; plasma LCAT protein concentration was 0.56 microg/ml and equivalent to approximately 10% of normal LCAT mass. Analysis by single strand conformation polymorphism (SSCP) of the PCR products corresponding to exons 4 and 5 of the LCAT gene revealed a visible band shift. Sequence analyses of exons 4 + 5 revealed two separate single point mutations: a C --> T transition replacing Arg147 by Trp and a T --> G transition converting Tyr171 to a stop codon. The presence of these two point mutations was confirmed by restriction enzyme analyses: the C --> T transition abolished a MwoI site whereas the T --> G transition created an AvrII site. The Arg147 mutation was associated with a non-secreted protein. The Tyr171 mutation resulted in formation of a truncated protein lacking the catalytic site. In summary, we have identified an LCAT deficient patient corresponding to a compound heterozygote for the Arg147 --> Trp mutation and a new molecular defect involving a Tyr171 --> Stop mutation in the LCAT gene.