Characterization of a new LCAT mutation causing familial LCAT deficiency (FLD) and the role of APOE as a modifier gene of the FLD phenotype

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.

Current Status of Familial LCAT Deficiency in Japan

Lecithin cholesterol acyltransferase (LCAT) is a lipid-modification enzyme that catalyzes the transfer of the acyl chain from the second position of lecithin to the hydroxyl group of cholesterol (FC) on plasma lipoproteins to form cholesteryl acylester and lysolecithin. Familial LCAT deficiency is an intractable autosomal recessive disorder caused by inherited dysfunction of the LCAT enzyme. The disease appears in two different phenotypes depending on the position of the gene mutation: familial LCAT deficiency (FLD, OMIM 245900) that lacks esterification activity on both HDL and ApoB-containing lipoproteins, and fish-eye disease (FED, OMIM 136120) that lacks activity only on HDL. Impaired metabolism of cholesterol and phospholipids due to LCAT dysfunction results in abnormal concentrations, composition and morphology of plasma lipoproteins and further causes ectopic lipid accumulation and/or abnormal lipid composition in certain tissues/cells, and serious dysfunction and complications in certain organs. Marked reduction of plasma HDL-cholesterol (HDL-C) and corneal opacity are common clinical manifestations of FLD and FED. FLD is also accompanied by anemia, proteinuria and progressive renal failure that eventually requires hemodialysis. Replacement therapy with the LCAT enzyme should prevent progression of serious complications, particularly renal dysfunction and corneal opacity. A clinical research project aiming at gene/cell therapy is currently underway.

Progression of chronic kidney disease in familial LCAT deficiency: a follow-up of the Italian cohort

Familial LCAT deficiency (FLD) is a rare genetic disorder of HDL metabolism, caused by loss-of-function mutations in the LCAT gene and characterized by a variety of symptoms including corneal opacities and kidney failure. Renal disease represents the leading cause of morbidity and mortality in FLD cases. However, the prognosis is not known and the rate of deterioration of kidney function is variable and unpredictable from patient to patient. In this article, we present data from a follow-up of the large Italian cohort of FLD patients, who have been followed for an average of 12 years. We show that renal failure occurs at the median age of 46 years, with a median time to a second recurrence of 10 years. Additionally, we identify high plasma unesterified cholesterol level as a predicting factor for rapid deterioration of kidney function. In conclusion, this study highlights the severe consequences of FLD, underlines the need of correct early diagnosis and referral of patients to specialized centers, and highlights the urgency for effective treatments to prevent or slow renal disease in patients with LCAT deficiency.

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.

Dysbetalipoproteinaemia: a mixed hyperlipidaemia of remnant lipoproteins due to mutations in apolipoprotein E

Atherosclerosis is strongly associated with dyslipoproteinaemia, and especially with increasing concentrations of low-density lipoprotein and decreasing concentrations of high-density lipoproteins. Its association with increasing concentrations of plasma triglyceride is less clear but, within the mixed hyperlipidaemias, dysbetalipoproteinaemia (Fredrickson type III hyperlipidaemia) has been identified as a very atherogenic entity associated with both premature ischaemic heart disease and peripheral arterial disease. Dysbetalipoproteinaemia is characterized by the accumulation of remnants of chylomicrons and of very low-density lipoproteins. The onset occurs after childhood and usually requires an additional metabolic stressor. In women, onset is typically delayed until menopause. Clinical manifestations may vary from no physical signs to severe cutaneous and tendinous xanthomata, atherosclerosis of coronary and peripheral arteries, and pancreatitis when severe hypertriglyceridaemia is present. Rarely, mutations in apolipoprotein E are associated with lipoprotein glomerulopathy, a condition characterized by progressive proteinuria and renal failure with varying degrees of plasma remnant accumulation. Interestingly, predisposing genetic causes paradoxically result in lower than average cholesterol concentration for most affected persons, but severe dyslipidaemia develops in a minority of patients. The disorder stems from dysfunctional apolipoprotein E in which mutations result in impaired binding to low-density lipoprotein (LDL) receptors and/or heparin sulphate proteoglycans. Apolipoprotein E deficiency may cause a similar phenotype. Making a diagnosis of dysbetalipoproteinaemia aids in assessing cardiovascular risk correctly and allows for genetic counseling. However, the diagnostic work-up may present some challenges. Diagnosis of dysbetalipoproteinaemia should be considered in mixed hyperlipidaemias for which the apolipoprotein B concentration is relatively low in relation to the total cholesterol concentration or when there is significant disparity between the calculated LDL and directly measured LDL cholesterol concentrations. Genetic tests are informative in predicting the risk of developing the disease phenotype and are diagnostic only in the context of hyperlipidaemia. Specialised lipoprotein studies in reference laboratory centres can also assist in diagnosis. Fibrates and statins, or even combination treatment, may be required to control the dyslipidaemia.

DNA methylation variations at CETP and LPL gene promoter loci: new molecular biomarkers associated with blood lipid profile variability

BACKGROUND

Recent findings suggest that DNA methylation, a well-known epigenetic mechanism, is involved in high-density lipoprotein cholesterol (HDL-C) metabolism and increased cardiovascular disease risk. The aim of this study was thus to assess whether DNA methylation within key genes of lipoprotein metabolism is associated with blood lipid profile variability.

METHODS AND RESULTS

Ninety-eight untreated familial hypercholesterolaemia patients (61 men and 37 women) were recruited for leucocyte DNA methylation analyses at the LDLR, CETP, LCAT and LPL gene promoter loci using bisulfite pyrosequencing. LPL DNA methylation was correlated with HDL-C (r = 0.22; p = 0.031) and HDL particle size (r = 0.47, p = 0.013). In both sex, CETP DNA methylation was negatively associated with low-density lipoprotein cholesterol levels (r < -0.32; p < 0.05). In men, CETP DNA methylation was associated with HDL-C (r = -0.36; p = 0.006), HDL-triglyceride levels (r = 0.59; p < 0.001) and HDL particle size (r = -0.44, p = 0.019). In visceral adipose tissue from 30 men with severe obesity, the associations between LPL DNA methylation, HDL-C (r = -0.40; p = 0.03) and LPL mRNA levels (r = -0.61, p < 0.001) were confirmed.

CONCLUSION

CETP and LPL DNA methylation levels are associated with blood lipid profile, suggesting that further studies of epipolymorphisms should most certainly contribute to a better understanding of the molecular bases of dyslipidemia.

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

BACKGROUND

A case of homozygous familial lecithin:cholesterol acyltransferase (LCAT) deficiency with a novel homozygous LCAT missense mutation (replacement of methionine by arginine at position 293 in the amino acid sequence of the LCAT protein) is reported.

METHODS AND RESULTS

The probable diagnosis was suggested by findings of marked high density lipoprotein (HDL) deficiency, corneal opacification, anemia, and renal insufficiency. The diagnosis was confirmed by two dimensional gel electrophoresis of HDL, the measurement of free and esterified cholesterol, and sequencing of the LCAT gene.

CONCLUSIONS

In our view the most important aspects of therapy to prevent the kidney disease that these patients develop is careful control of blood pressure and lifestyle measures to optimize non HDL lipoproteins. In the future replacement therapy by gene transfer or other methods may become available.

Two novel mutations of lecithin:cholesterol acyltransferase (LCAT) gene and the influence of APOE genotypes on clinical manifestations

Familial lecithin:cholesterol acyltransferase deficiency (FLD) is an autosomal recessive disorder characterized by corneal opacity, hemolytic anemia, low high-density lipoprotein cholesterol (HDL-C) and proteinuria. Two novel lecithin:cholesterol acyltransferase (LCAT) mutations[c.278 C>T (p.Pro69Leu); c.950 T>C (p.Met293Thr)] were identified in a 27-year-old man and in a 30-year-old woman, respectively. Both patients manifested corneal opacity, hemolytic anemia, low low-density lipoprotein cholesterol and HDL-C and proteinuria. Lipid deposits with vacuolar lucent appearance in glomerular basement membranes were observed in both cases. APOE genotype was also investigated: the first case results ϵ4/ϵ3, the second ϵ2/ϵ2; however, they shared a similar phenotype characterized by the presence of intermediate-density lipoproteins (IDL) remnant and the absence of lipoprotein-X. In conclusion, our findings suggest that APOE ϵ2/ϵ2 may not be the major determinant gene for the appearance of IDL in FLD patients.

Molecular analysis of a novel LCAT mutation (Gly179 → Arg) found in a patient with complete LCAT deficiency

Lecithin-cholesterol acyltransferase (LCAT) is an important enzyme involved in the esterification of cholesterol. Here, we report a novel point mutation in the LCAT gene of a 63-year-old female with characteristics of classic familial LCAT deficiency. The patient's clinical manifestations included corneal opacity, mild anemia, mild proteinuria and normal renal function. She had no sign of coronary heart disease. Her LCAT activity was extremely low. DNA sequencing revealed a point mutation in exon 5 of the LCAT gene: a G to C substitution converting Gly(179) to an Arg, located in one of the catalytic triads of the enzyme. In vitro expression of recombinant LCAT proteins in HEK293 cells showed that the mutant G179R protein was present in the cell lysate, but not the culture medium. LCAT activity was barely detectable in the cell lysate or medium of the cells expressing the G179R mutant. This novel missense mutation seems to cause a complete loss of catalytic activity of LCAT, which is also defective in secretion.

Marked HDL deficiency and premature coronary heart disease

PURPOSE OF REVIEW

Our purpose is to review recent publications in the area of marked human HDL deficiency, HDL particles, coronary heart disease (CHD), amyloidosis, the immune response, and kidney disease.

RECENT FINDINGS

Lack of detectable plasma apolipoprotein (apo) A-I can be due to DNA deletions, rearrangements, or nonsense or frameshift mutations within the APOA1 gene resulting in a lack of apoA-I secretion. Such patients have marked HDL deficiency, normal levels of triglycerides and LDL cholesterol, and can have xanthomas and premature CHD. ApoA-I variants with amino acid substitutions, especially in the region of amino acid residues 50-93 and 170-178, have been associated with amyloidosis. Patients with homozygous Tangier disease have defective cellular cholesterol efflux due to mutations in the adenosine triphosphate-binding cassette transporter A1, detectable plasma apoA-I levels and prebeta-1 HDL in their plasma. They have decreased LDL cholesterol levels and can develop neuropathy and premature CHD. Patients with lecithin: cholesterol acyltransferase deficiency have both prebeta-1 and alpha-4 HDL present in their plasma and develop corneal opacities, anemia, proteinuria, and kidney failure.

SUMMARY

Patients with marked HDL deficiency can have great differences in their clinical phenotype depending on the underlying defect.