Lecithin: cholesterol acyltransferase deficiency: identification of two defective alleles in fibroblast cDNA

Longitudinal analysis of clinical and laboratory biomarkers in a patient with familial lecithin: cholesterol acyltransferase deficiency (FLD) and accelerated eGFR decline: A case study

Familial lecithin:cholesterol acyltransferase (LCAT) deficiency (FLD) is an ultra-rare autosomal recessive disease characterized by very low high-density lipoprotein cholesterol (HDL-C) levels, corneal opacity, anemia, and progressive renal disease. The rate and severity of renal disease are variable across FLD patients and the biomarkers and risk factors for disease progression are poorly understood. Here we report a 30 year-long comparative analysis of the clinical and laboratory biomarkers in an FLD patient with accelerated renal decline, who underwent two kidney and one liver transplantations. Results show that elevated triglyceride and non-HDL-C levels may promote the formation of LpX and accelerate renal function decline, whereas markers of anemia may be early predictors. Conversely, corneal opacity progresses at a steady rate and does not correlate with lipid, hematologic, or renal biomarkers. Our study suggests that monitoring of markers of anemia may aid the early detection and timely management of kidney disease with conservative therapies. Furthermore, it suggests that controlling hypercholesterolemia and hypertriglyceridemia may help improve renal disease prognosis.

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.

Allele-specific enhancers mediate associations between LCAT and ABCA1 polymorphisms and HDL metabolism

For most complex traits, the majority of SNPs identified through genome-wide association studies (GWAS) reside within noncoding regions that have no known function. However, these regions are enriched for the regulatory enhancers specific to the cells relevant to the specific trait. Indeed, many of the GWAS loci that have been functionally characterized lie within enhancers that regulate expression levels of key genes. In order to identify polymorphisms with potential allele-specific regulatory effects, we developed a bioinformatics pipeline that harnesses epigenetic signatures as well as transcription factor (TF) binding motifs to identify putative enhancers containing a SNP with potential allele-specific TF binding in linkage disequilibrium (LD) with a GWAS-identified SNP. We applied the approach to GWAS findings for blood lipids, revealing 7 putative enhancers harboring associated SNPs, 3 of which lie within the introns of LCAT and ABCA1, genes that play crucial roles in cholesterol biogenesis and lipoprotein metabolism. All 3 enhancers demonstrated allele-specific in vitro regulatory activity in liver-derived cell lines. We demonstrated that these putative enhancers are in close physical proximity to the promoters of their respective genes, in situ, likely through chromatin looping. In addition, the associated alleles altered the likelihood of transcription activator STAT3 binding. Our results demonstrate that through our approach, the LD blocks that contain GWAS signals, often hundreds of kilobases in size with multiple SNPs serving as statistical proxies to the true functional site, can provide an experimentally testable hypothesis for the underlying regulatory mechanism linking genetic variants to complex traits.

Sequential kidney-liver transplantation from the same living donor for lecithin cholesterol acyl transferase deficiency

BACKGROUND

Lecithin cholesterol acyl transferase (LCAT) deficiency is a rare autosomal recessive disorder of lipoprotein metabolism that results in end-stage renal disease (ESRD) necessitating transplantation. As LCAT is produced in the liver, combined kidney and liver transplantation was proposed to cure the clinical syndrome of LCAT deficiency.

METHODS

A 29-year-old male with ESRD secondary to LCAT deficiency underwent a sequential kidney-liver transplantation from the same living donor (LD). One year following the kidney transplant, auxiliary partial orthotopic liver transplant (APOLT) of a left lateral segment from the same donor was performed.

RESULTS

At 5 years follow-up, there have been no major complications, readmissions, or rejection episodes. Serum lipid abnormalities recurred within the first year, but liver and kidney allograft function remains intact.

CONCLUSION

Few cases of sequential transplantation from the same LD have been performed in adults. This is the first APOLT and multi-organ transplant performed for LCAT deficiency. Sequential organ transplant from the same LD for ESRD secondary to a metabolic disorder of the liver is feasible in adults and should be further investigated.

Proteinuria in early childhood due to familial LCAT deficiency caused by loss of a disulfide bond in lecithin:cholesterol acyl transferase

INTRODUCTION

Familial lecithin:cholesterol acyltransferase (LCAT) deficiency (FLD) is a rare recessive disorder of cholesterol metabolism characterized by the absence of high density lipoprotein (HDL) and the triad of corneal opacification, hemolytic anemia and glomerulopathy.

PATIENTS

We here report on FLD in three siblings of a kindred of Moroccan descent with HDL deficiency. In all cases (17, 12 and 3 years of age) corneal opacification and proteinuria were observed. In the 17-year-old female proband, anemia with target cells was observed.

RESULTS

Homozygosity for a mutation in LCAT resulted in the exchange of cysteine to tyrosine at position 337, disrupting the second disulfide bond in LCAT. LCAT protein and activity were undetectable in the patients' plasma and in media of COS7 cells transfected with an expression vector with mutant LCAT cDNA. Upon treatment with an ACE inhibitor and a thiazide diuretic, proteinuria in the proband decreased from 6g to 2g/24h.

CONCLUSION

This is the first report that FLD can cause nephropathy at a very early age.

Do mutations causing low HDL-C promote increased carotid intima-media thickness?

BACKGROUND

Although observational data support an inverse relationship between high-density lipoprotein (HDL) cholesterol and coronary heart disease (CHD), genetic HDL deficiency states often do not correlate with premature CHD.

METHODS

Carotid intima-media thickness (cIMT) measurements were obtained in cases comprising 10 different mutations in LCAT, ABCA1 and APOA1 to further evaluate the relationship between low HDL resulting from genetic variation and early atherosclerosis.

RESULTS

In a 1:2 case-control study of sex and age-related (+/-5 y) subjects (n=114), cIMT was nearly identical between cases (0.66+/-0.17 cm) and controls (0.65+/-0.18 cm) despite significantly lower HDL cholesterol (0.67 vs. 1.58 mmol/l) and apolipoprotein A-I levels (96.7 vs. 151.4 mg/dl) (P<0.05)

CONCLUSIONS

Genetic variants identified in the present study may be insufficient to promote early carotid atherosclerosis.

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.

Apolipoprotein A-I(Zavalla) (Leu159-->Pro): HDL cholesterol deficiency in a kindred associated with premature coronary artery disease

We investigated the molecular defect causing high density lipoprotein cholesterol (HDL-C) deficiency in a male proband and his family members. Amplification and sequencing of genomic DNA disclosed a novel base-pair substitution at residue 159 in the apolipoprotein (apo) A-I gene. This substitution resulted in the loss of an AviII restriction site and a predicted substitution of leucine with proline at residue 159. Restriction enzyme analysis demonstrated absence of the AviII site in 19 of 40 biological family members. Compared with familial controls, subjects with the apoA-I(Zavalla) variant had reduced HDL-C (1.16 versus 0.27 mmol/L, P<0.0001), apoA-I (38.7 versus 124.4 mg/dL, P<0.0001), and apoA-II (14.3 versus 19.0 mg/dL, P<0.0001) levels. Two subjects who have developed coronary artery disease to date possess additional cardiovascular risk factors. Other heterozygotes for apoA-I(Zavalla) are presently without symptomatic coronary artery disease. This study identifies a monogenic cause of hypoalphalipoproteinemia, with the single base-pair substitution having a dominant effect on the low HDL-C phenotype. In addition, it extends recent observations that HDL-C deficiency states may be more prone to the development of premature coronary artery disease when accompanied by additional cardiovascular risk factors.

Alternative splicing in lecithin:cholesterol acyltransferase mRNA: an evolutionary paradigm in humans and great apes

Lecithin:cholesterol acyltransferase (LCAT), an important enzyme affecting reverse cholesterol transport, is expressed in liver and cultured fibroblasts. Sequencing of LCAT cDNA clones demonstrated the coexistence of two mRNA products. In addition to the normal transcript, we identified an alternate message with a splice-mediated insertion of a 95 bp Alu cassette at the junction of exons 5 and 6. In humans, the alternate transcript represents 5-20% of the complete LCAT message in cultured fibroblasts and liver. It is present in humans and the great apes but not in lesser apes (gibbon, siamang) or lower-order primates (e.g., old or new world monkeys). Sequencing of intron 5 of the LCAT locus in several primates revealed a G-->A transition at the splice donor recognition site in the Alu repeat of the gibbon and a G-->A substitution in the last position of the 95 bp Alu sequence of the rhesus monkey, an old world monkey. Both substitutions have been associated with exon skipping in other genes. These results demonstrate that alternative splicing of LCAT mRNA is variant among primates and suggest a potential role of Alu elements in the evolutionary diversity of proteins.

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.