Lecithin cholesterol acyltransferase deficiency

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Lipid Disorders Main Page

Overview

Causes

Classification

Abetalipoproteinemia
Hypobetalipoproteinemia
Familial hypoalphalipoproteinemia
LCAT Deficiency
Chylomicron retention disease
Tangier disease
Familial combined hypolipidemia

Differential Diagnosis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Aravind Kuchkuntla, M.B.B.S[2]

Synonyms and keywords: LCAT deficiency, dyslipoproteinemic corneal dystrophy, fish eye disease, Norum disease, partial LCAT deficiency

Overview

Historical Perspective

  • In 1962, Glomset identified an enzyme (plasma fatty acid transferase) which transfers fatty acid onto free cholesterol to make a cholesterol ester. This helps in the formation of a mature HDL particle a crucial step in reverse cholesterol transport [1].
  • In 1967, Norum and Gjone described a disease for the first time in a patient from Norway with features of normochromic anemia, protienuria and corneal lipid deposits[2].
  • In 1967, Norum and Gjone reported that two sisters of the affected patient had similar presentation along with low levels of cholesterol esters and lysolecithin in the serum, with increased total body cholesterol, triglyceride and phospholipid. Foam cells in the bone marrow and glomerulus were demonstrated on microscopy. Patients had absent hepatomegaly and normal tonsils differentiating it from liver disease causing the defect in esterification and Tangier disease. Low serum cholesterol esters were attributed to the LCAT enzyme deficiency[3].
  • In 1986, McLean and colleagues reported the complete gene sequence and sites expression of Lecithin cholesterol acyl transferase gene(LCAT). The location of the gene is identified to be on q21-22 region of chromosome 16 [4] and is synthesized mainly in the liver.

Demographics, Natural History and Complications

Pathophysiology

Pathogenesis

LCAT Function

  • Majority of the enzyme is associated with HDL C, very small amount with LDL C[5].
 
 
 
LCAT synthesized in liver and released into circulation and is picked up by HDL C
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Apo A1 activates LCAT
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
LCAT cleaves fatty acid from phosphotidylcholine
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Transfers fatty acid to beta hydroxyl group of free cholesterol(FC) taken up by HDL C
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Results in the formation of cholesterol esters which help in maturation of HDL C and also forms lysophosphotidylcholine
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Esterification of FC taken up by HDL C, is Alpha LCAT activity. Esterification of FC associated with Apo B ( LDL C), is β-LCAT activity. This differntiation into alpha and beta is based on the HDL and LDL mobility on electrophoresis
 
 
 
  • LCAT helps in reverse cholesterol transport by:[6]
    • Cholesterol esters due to the hydrophobic nature occupy the core of the lipoprotien, which prevent the backflow of cholesterol into the cells.
    • LCAT promotes unidirectional efflux of free cholesterol from the cells via ABCA1 and scavenger receptor type B-I (SR-BI) by creating a concentration gradient.

LCAT Deficiency

 
 
 
Loss of LCAT function
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Loss of alpha function leads to failure HDL maturation resulting in elevated FC, phospholipids, Apo E and pre beta HDL and low Apo A1 and Apo A2 levels
 
 
 
Loss of beta function results in elevated FC, phospholipids and formation of cholesterol rich particle called Lipoprotien X [7], which are implicated in the development of glomerulopathy[8].

Genetics

  • Autosomal Recessive.
  • LCAT gene is on chromosome 16.
  • Expression of clinical features and severity of disease in homozygous patients depends on the type and locus of the mutation[9].

Microscopy

Classification

Severity of the disease is a direct result of the enzyme deficiency. Mutation can cause either a complete loss of function or a partial loss of function, based on which LCAT deficiency can be classified into:[10]

  • Familial LCAT deficiency: Complete loss of alpha and beta LCAT function.
  • Fish Eye Disease: Loss of alpha LCAT function and preserved beta fucntion.
Familial LCAT deficiency Fish Eye Disease
Enzyme Defect Complete loss Loss of alpha function only
Clinical Features Corneal opacities, anaemia

and progressive renal disease with protienuria

Corneal opacities only

Normal renal function

Microscopy Deposition of FC and phospholipids

in cornea and RBC membrane.

Lipoprotien-X deposition in the glomerulus.

Deposition of FC and phospolipids

in the cornea.

Laboratory findings Elevated Free cholesterol

Very low HDL C

Low Apo A1 and Apo A2

Elevated Apo E

Low LDL C

Elevated free cholesterol

Very low HDL C

Low Apo A1 and Apo A2

Elevated Apo E

Normal LDL and VLDL

Diagnosis

History and Symptoms

Laboratory Findings

Others

Treatment

Medical Therapy

Surgical Therapy

References

  1. GLOMSET JA (1962). "The mechanism of the plasma cholesterol esterification reaction: plasma fatty acid transferase". Biochim Biophys Acta. 65: 128–35. PMID 13948499.
  2. Norum KR, Gjone E (1967). "Familial serum-cholesterol esterification failure. A new inborn error of metabolism". Biochim Biophys Acta. 144 (3): 698–700. PMID 6078131.
  3. Gjone E, Norum KR (1968). "Familial serum cholesterol ester deficiency. Clinical study of a patient with a new syndrome". Acta Med Scand. 183 (1–2): 107–12. PMID 5669813.
  4. McLean J, Wion K, Drayna D, Fielding C, Lawn R (1986). "Human lecithin-cholesterol acyltransferase gene: complete gene sequence and sites of expression". Nucleic Acids Res. 14 (23): 9397–406. PMC 311966. PMID 3797244.
  5. Chen CH, Albers JJ (1982). "Distribution of lecithin-cholesterol acyltransferase (LCAT) in human plasma lipoprotein fractions. Evidence for the association of active LCAT with low density lipoproteins". Biochem Biophys Res Commun. 107 (3): 1091–6. PMID 7138515.
  6. Tall AR (1990). "Plasma high density lipoproteins. Metabolism and relationship to atherogenesis". J Clin Invest. 86 (2): 379–84. doi:10.1172/JCI114722. PMC 296738. PMID 2200802.
  7. Narayanan S (1984). "Biochemistry and clinical relevance of lipoprotein X." Ann Clin Lab Sci. 14 (5): 371–4. PMID 6476782.
  8. Ossoli A, Neufeld EB, Thacker SG, Vaisman B, Pryor M, Freeman LA; et al. (2016). "Lipoprotein X Causes Renal Disease in LCAT Deficiency". PLoS One. 11 (2): e0150083. doi:10.1371/journal.pone.0150083. PMC 4769176. PMID 26919698.
  9. Gotoda T, Yamada N, Murase T, Sakuma M, Murayama N, Shimano H; et al. (1991). "Differential phenotypic expression by three mutant alleles in familial lecithin:cholesterol acyltransferase deficiency". Lancet. 338 (8770): 778–81. PMID 1681161.
  10. McIntyre N (1988). "Familial LCAT deficiency and fish-eye disease". J Inherit Metab Dis. 11 Suppl 1: 45–56. PMID 3141686.


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