Homozygous lecithin:cholesterol acyltransferase (LCAT) deficiency due to a new loss of function mutation and review of the literature

A systematic review of the natural history and biomarkers of primary Lecithin:Cholesterol Acyltransferase (LCAT) 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.

Selective Correction of Genotype Yield by Probucol in HDL-Deficient Mice Propagation

Aim: Probucol is a controversial drug to inhibit ATP-binding cassette transporter A1 (ABCA1) and to exhibit some positive clinical effects such as regression of xanthomas. It reportedly rescues female infertility in scavenger receptor BI-deficient mice. Here, we investigated the effect of probucol on propagation in HDL-deficient mice as alternative models for impaired HDL-mediated cholesterol delivery.

Methods: Propagation of ABCA1-deficient (Abca1−/−) mice and lecithin: cholesterol acyltransferase (LCAT)-deficient (Lcat−/−) mice were quantitatively observed under the probucol treatment.

Results:Abca1−/− and Lcat−/− mice appear with negligible plasma HDL concentration. Upon backcrossing Abc1+/− with the Abc1−/− mice and cross-breeding between Abc1+/− mice, the numbers of Abc1−/− weaned pups were reduced to 54.7% and to 57.1% from those expected by Mendelian genetics, respectively. Similarly, Lcat-/-weaned pups decreased to 67.7% and to 35.9% but only in the male. Probucol severely reduced plasma HDL-cholesterol to 5% in the wild-type mice, but showed no effects on their propagation. Probucol corrected the deflections of the genotype distribution in the weaned pups recovery in the LCAT-deficient mice propagation but not in the ABCA1-deficient mice while plasma HDL was kept negligible. Probucol had no effect on cholesterol content in the steroidogenic organs of the HDL-deficient mice, while it somewhat increased plasma corticosterone and expression of adrenal cortex HMG-CoA reductase, StAR, cytochrome P450scc, and VKORC1 indicating increase in the synthesis of cholesterol and steroid hormones and in vitamin K turn-over. However, no evident mechanistic background was indicated.

Conclusions: Probucol corrected deflection of genotype distribution in propagation of the LCAT-deficient mice but not the ABCA1-deficient mice at the weaning stage, apparently not through normalization of hypoalphalipo-proteinemia.

Finding a very rare mutation in non-Caucasian LCAT patients from Southwest Asia for the first time

INTRODUCTION

Lecithin cholesterol acyltransferase (LCAT) deficiency is an autosomal recessive disorder occurred by different mutations in the LCAT gene that cause two extremely rare syndromes including familial LCAT deficiency (FLD) and fish-eye disease (FED). Unlike FED in FLD renal failure is the most important defect due to deposition of abnormal lipoproteins in the renal stroma. In this study, FLD patients from the North of Iran were investigated for mutations in the LCAT gene.

MATERIALS AND METHODS

Eight patients with corneal opacification and renal defect were analyzed for mutations in the LCAT gene by PCR sequencing.

RESULTS

Sequencing analysis revealed a missense pathogenic variation c.301 G>A in exon 2 of LCAT gene in all patients changing the amino acid aspartate to asparagine at the conserved position of amino acid 101 of LCAT protein.

CONCLUSION

In this study, a very rare variation was reported for the first time in this part of the world. Investigation of a larger number of LCAT patients in different parts of Iran can provide availability of mutations panel that is useful for phenotype prediction and also prenatal diagnosis programming in families with a previous history of the disease.

Genetic and secondary causes of severe HDL deficiency and cardiovascular disease

We assessed secondary and genetic causes of severe HDL deficiency in 258,252 subjects, of whom 370 men (0.33%) and 144 women (0.099%) had HDL cholesterol levels <20 mg/dl. We excluded 206 subjects (40.1%) with significant elevations of triglycerides, C-reactive protein, glycosylated hemoglobin, myeloperoxidase, or liver enzymes and men receiving testosterone. We sequenced 23 lipid-related genes in 201 (65.3%) of 308 eligible subjects. Mutations (23 novel) and selected variants were found at the following gene loci: 1) ABCA1 (26.9%): 2 homozygotes, 7 compound or double heterozygotes, 30 heterozygotes, and 2 homozygotes and 13 heterozygotes with variants rs9282541/p.R230C or rs111292742/c.-279C>G; 2) LCAT (12.4%): 1 homozygote, 3 compound heterozygotes, 13 heterozygotes, and 8 heterozygotes with variant rs4986970/p.S232T; 3) APOA1 (5.0%): 1 homozygote and 9 heterozygotes; and 4) LPL (4.5%): 1 heterozygote and 8 heterozygotes with variant rs268/p.N318S. In addition, 4.5% had other mutations, and 46.8% had no mutations. Atherosclerotic cardiovascular disease (ASCVD) prevalence rates in the ABCA1, LCAT, APOA1, LPL, and mutation-negative groups were 37.0%, 4.0%, 40.0%, 11.1%, and 6.4%, respectively. Severe HDL deficiency is uncommon, with 40.1% having secondary causes and 48.8% of the subjects sequenced having ABCA1, LCAT, APOA1, or LPL mutations or variants, with the highest ASCVD prevalence rates being observed in the ABCA1 and APOA1 groups.

A novel homozygous mutation causing lecithin-cholesterol acyltransferase deficiency in a proband of Romanian origin with a record of extreme gestational hyperlipidemia

A patient from Romania with extraordinarily high total cholesterol levels and clinical and biochemical features consistent with familial lecithin-cholesterol acyltransferase deficiency is reported. The genetic analysis performed on our proband showed a novel homozygous mutation on codon 119 of lecithin-cholesterol acyltransferase gene that causes the substitution of glycine by aspartate. The same mutation, also in homozygosis, was observed in her older sister, whereas his brother presented it in heterozygosis.

Diagnosis and treatment of high density lipoprotein deficiency

Low serum high density lipoprotein cholesterol level (HDL-C) <40 mg/dL in men and <50 mg/dL in women is a significant independent risk factor for cardiovascular disease (CVD), and is often observed in patients with hypertriglyceridemia, obesity, insulin resistance, and diabetes. Patients with marked deficiency of HDL-C (<20 mg/dL) in the absence of secondary causes are much less common (<1% of the population). These patients may have homozygous, compound heterozygous, or heterozygous defects involving the apolipoprotein (APO)AI, ABCA1, or lecithin:cholesterol acyl transferase genes, associated with apo A-I deficiency, apoA-I variants, Tangier disease , familial lecithin:cholesteryl ester acyltransferase deficiency, and fish eye disease. There is marked variability in laboratory and clinical presentation, and DNA analysis is necessary for diagnosis. These patients can develop premature CVD, neuropathy, kidney failure, neuropathy, hepatosplenomegaly and anemia. Treatment should be directed at optimizing all non-HDL risk factors.

A Systematic Investigation of Structure/Function Requirements for the Apolipoprotein A-I/Lecithin Cholesterol Acyltransferase Interaction Loop of High-density Lipoprotein

The interaction of lecithin-cholesterol acyltransferase (LCAT) with apolipoprotein A-I (apoA-I) plays a critical role in high-density lipoprotein (HDL) maturation. We previously identified a highly solvent-exposed apoA-I loop domain (Leu(159)-Leu(170)) in nascent HDL, the so-called "solar flare" (SF) region, and proposed that it serves as an LCAT docking site (Wu, Z., Wagner, M. A., Zheng, L., Parks, J. S., Shy, J. M., 3rd, Smith, J. D., Gogonea, V., and Hazen, S. L. (2007) Nat. Struct. Mol. Biol. 14, 861-868). The stability and role of the SF domain of apoA-I in supporting HDL binding and activation of LCAT are debated. Here we show by site-directed mutagenesis that multiple residues within the SF region (Pro(165), Tyr(166), Ser(167), and Asp(168)) of apoA-I are critical for both LCAT binding to HDL and LCAT catalytic efficiency. The critical role for possible hydrogen bond interaction at apoA-I Tyr(166) was further supported using reconstituted HDL generated from apoA-I mutants (Tyr(166) → Glu or Asn), which showed preservation in both LCAT binding affinity and catalytic efficiency. Moreover, the in vivo functional significance of NO2-Tyr(166)-apoA-I, a specific post-translational modification on apoA-I that is abundant within human atherosclerotic plaque, was further investigated by using the recombinant protein generated from E. coli containing a mutated orthogonal tRNA synthetase/tRNACUA pair enabling site-specific insertion of the unnatural amino acid into apoA-I. NO2-Tyr(166)-apoA-I, after subcutaneous injection into hLCAT(Tg/Tg), apoA-I(-/-) mice, showed impaired LCAT activation in vivo, with significant reduction in HDL cholesteryl ester formation. The present results thus identify multiple structural features within the solvent-exposed SF region of apoA-I of nascent HDL essential for optimal LCAT binding and catalytic efficiency.

Structural Insights into High Density Lipoprotein: Old Models and New Facts

The physiological link between circulating high density lipoprotein (HDL) levels and cardiovascular disease is well-documented, albeit its intricacies are not well-understood. An improved appreciation of HDL function and overall role in vascular health and disease requires at its foundation a better understanding of the lipoprotein's molecular structure, its formation, and its process of maturation through interactions with various plasma enzymes and cell receptors that intervene along the pathway of reverse cholesterol transport. This review focuses on summarizing recent developments in the field of lipid free apoA-I and HDL structure, with emphasis on new insights revealed by newly published nascent and spherical HDL models constructed by combining low resolution structures obtained from small angle neutron scattering (SANS) with contrast variation and geometrical constraints derived from hydrogen-deuterium exchange (HDX), crosslinking mass spectrometry, electron microscopy, Förster resonance energy transfer, and electron spin resonance. Recently published low resolution structures of nascent and spherical HDL obtained from SANS with contrast variation and isotopic labeling of apolipoprotein A-I (apoA-I) will be critically reviewed and discussed in terms of how they accommodate existing biophysical structural data from alternative approaches. The new low resolution structures revealed and also provided some answers to long standing questions concerning lipid organization and particle maturation of lipoproteins. The review will discuss the merits of newly proposed SANS based all atom models for nascent and spherical HDL, and compare them with accepted models. Finally, naturally occurring and bioengineered mutations in apoA-I, and their impact on HDL phenotype, are reviewed and discuss together with new therapeutics employed for restoring HDL function.

Familial lecithin:cholesterol acyltransferase deficiency: First-in-human treatment with enzyme replacement

BACKGROUND

Humans with familial lecithin:cholesterol acyltransferase (LCAT) deficiency (FLD) have extremely low or undetectable high-density lipoprotein cholesterol (HDL-C) levels and by early adulthood develop many manifestations of the disorder, including corneal opacities, anemia, and renal disease.

OBJECTIVE

To determine if infusions of recombinant human LCAT (rhLCAT) could reverse the anemia, halt progression of renal disease, and normalize HDL in FLD.

METHODS

rhLCAT (ACP-501) was infused intravenously over 1 hour on 3 occasions in a dose optimization phase (0.3, 3.0, and 9.0 mg/kg), then 3.0 or 9.0 mg/kg every 1 to 2 weeks for 7 months in a maintenance phase. Plasma lipoproteins, lipids, LCAT levels, and several measures of renal function and other clinical labs were monitored.

RESULTS

LCAT concentration peaked at the end of each infusion and decreased to near baseline over 7 days. Renal function generally stabilized or improved and the anemia improved. After infusion, HDL-C rapidly increased, peaking near normal in 8 to 12 hours; analysis of HDL particles by various methods all revealed rapid sequential disappearance of preβ-HDL and small α-4 HDL and appearance of normal α-HDL. Low-density lipoprotein cholesterol increased more slowly than HDL-C. Of note, triglyceride routinely decreased after meals after infusion, in contrast to the usual postprandial increase in the absence of rhLCAT infusion.

CONCLUSIONS

rhLCAT infusions were well tolerated in this first-in-human study in FLD; the anemia improved, as did most parameters related to renal function in spite of advanced disease. Plasma lipids transiently normalized, and there was rapid sequential conversion of small preβ-HDL particles to mature spherical α-HDL particles.

Case report: A novel apolipoprotein A-I missense mutation apoA-I (Arg149Ser)Boston associated with decreased lecithin-cholesterol acyltransferase activation and cellular cholesterol efflux

We report a novel heterozygous apolipoprotein A-I (apoA-I) missense mutation (c.517C>A, p.Arg149Ser, designated as apoA-IBoston) in a 67-year-old woman and her 2 sons, who had mean serum high-density lipoprotein (HDL) cholesterol, apoA-I, and apoA-I in very large α-1 HDL that were 10%, 35%, and 16% of normal, respectively (all P < .05). The percentage of HDL cholesterol in the esterified form was also significantly (P < .05) reduced to 52% of control values. Cholesteryl ester tranfer protein (CETP) activity was normal. The mean global, adenosine triphosphate (ATP)-binding cassette transporter A1 and scavenger receptor B type I-mediated cellular cholesterol efflux capacity in apoB-depleted serum from affected family members were 41%, 37%, 47%, 54%, and 48% of control values, respectively (all P < .05). lecithin-cholesterol acyltransferase (LCAT) activity in plasma was 71% of controls, whereas in the cell-based assay, it was 73% of control values (P < .05). The data indicate that this novel apoA-I missense is associated with markedly decreased levels of HDL cholesterol and very large α-1 HDL, as well as decreased serum cellular cholesterol efflux and LCAT activity, but not with premature coronary heart disease, similar to other apoA-I mutations that have been associated with decreased LCAT activity.