A fish-eye disease-like familial condition with massive corneal clouding and dyslipoproteinemia. Report of clinical, histologic, electron microscopic, and biochemical features

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.

LCAT, ApoD, and ApoA1 Expression and Review of Cholesterol Deposition in the Cornea

Lecithin:cholesterol acyltransferase (LCAT) is an enzyme secreted by the liver and circulates with high-density lipoprotein (HDL) in the blood. The enzyme esterifies plasma cholesterol and increases the capacity of HDL to carry and potentially remove cholesterol from tissues. Cholesterol accumulates within the extracellular connective tissue matrix of the cornea stroma in individuals with genetic deficiency of LCAT. LCAT can be activated by apolipoproteins (Apo) including ApoD and ApoA1. ApoA1 also mediates cellular synthesis of HDL. This study examined the expression of LCAT by epithelial cells, keratocytes, and endothelial cells, the cell types that comprise from anterior to posterior the three layers of the cornea. LCAT and ApoD were immunolocalized to all three cell types within the cornea, while ApoA1 was immunolocalized to keratocytes and endothelium but not epithelium. In situ hybridization was used to detect LCAT, ApoD, and ApoA1 mRNA to learn what cell types within the cornea synthesize these proteins. No corneal cells showed mRNA for ApoA1. Keratocytes and endothelium both showed ApoD mRNA, but epithelium did not. Epithelium and endothelium both showed LCAT mRNA, but despite the presence of LCAT protein in keratocytes, keratocytes did not show LCAT mRNA. RNA sequencing analysis of serum-cultured dedifferentiated keratocytes (commonly referred to as corneal stromal fibroblasts) revealed the presence of both LCAT and ApoD (but not ApoA1) mRNA, which was accompanied by their respective proteins detected by immunolabeling of the cultured keratocytes and Western blot analysis of keratocyte lysates. The results indicate that keratocytes in vivo show both ApoA1 and LCAT proteins, but do not synthesize these proteins. Rather, keratocytes in vivo must take up ApoA1 and LCAT from the corneal interstitial tissue fluid.

Clinical features and visual function in a patient with Fish-eye disease: Quantitative measurements and optical coherence tomography

Purpose

We describe a case of fish-eye disease (FED) where the clinical features and visual function were investigated using anterior segment optical coherence tomography (OCT) and quantitative measurements.

Observations

A 36-year-old Japanese woman with FED presented with bilateral corneal opacities and visual complaints. Both contrast sensitivity and straylight were measured and OCT imaging was performed. Contrast sensitivity and straylight measurements revealed remarkably decreased visual function, despite good visual acuity. OCT demonstrated homogenously hyper-reflective corneal opacification, and a normal total corneal thickness.

Conclusions and Importance

The findings from this case suggest that OCT is useful for analyzing the clinical features of FED, and that the quantitative measurement of visual function furthers the understanding of vision-related symptoms in FED, despite good visual acuity.

In vivo imaging of the cornea in a patient with lecithin-cholesterol acyltransferase deficiency

PURPOSE

To report high-resolution, in vivo imaging of the cornea in a patient with lecithin-cholesterol acyltransferase (LCAT) deficiency.

METHODS

A 60-year-old Ecuadorian woman with bilateral corneal opacities and confirmed LCAT deficiency was imaged with Fourier domain optical coherence tomography (FD-OCT) and noncontact Rostock confocal laser scanning microscopy.

RESULTS

The FD-OCT revealed a thinned epithelium, homogeneous hyperreflective stroma, and focal disruptions of Bowman's layer. Focal areas of hyperreflectivity with multiple dark striae and reduced and irregular keratocytes were seen throughout the stroma by noncontact Rostock module. The corneal endothelium was normal.

CONCLUSION

New anterior segment in vivo imaging technology permits high-resolutional visualization and monitoring of corneal pathology.

Corneal clouding: An infrequent ophthalmic manifestation of mitochondrial disease

Corneal clouding is uncommon in infants and children but when present in this age group, it is often associated with mucopolysaccharidoses or Fabry disease. This report describes the case of an 11-year-old male who demonstrated poor weight gain, short stature, segmental myoclonus, and learning problems from 5 years of age followed by general weakness and extremely poor balance. Corneal clouding was evident as a result of a blurred vision complaint at 9 years of age. Both urine metabolic screening for mucopolysaccharidoses and analysis of lysosomal enzymes displayed negative findings. Clinical conditions worsened, including ptosis, progressive weakness, and positive Gowers' sign. Oral glucose lactate stimulation test was positive, therefore a muscle biopsy was performed at 11 years of age. Light microscopy of muscle biopsy disclosed abundant ragged red fibers; electron microscopy revealed abnormal mitochondria in terms of tubular cristae, concentrated cristae, stacking cristae, and round granular patterns of inclusion bodies in the matrix. Thus mitochondrial disease was diagnosed. We conclude that mitochondrial disease should be added to the list of differential diagnosis of corneal clouding in children, especially in cases with normal urine metabolic screening for mucopolysaccharidoses or when assays of lysosomal enzymes appear normal.

Possible induction of renal dysfunction in patients with lecithin:cholesterol acyltransferase deficiency by oxidized phosphatidylcholine in glomeruli

To clarify the causes of renal dysfunction in familial lecithin:cholesterol acyltransferase (LCAT) deficiency, kidney samples from 4 patients with LCAT deficiency (3 homozygotes and 1 heterozygote) were examined immunohistochemically. All of the patients exhibited corneal opacities, anemia, renal dysfunction, deficiencies in plasma high density lipoprotein and LCAT activity and mass, and an increase in the ratio of plasma unesterified cholesterol to esterified cholesterol. Renal lesions began with the deposition of lipidlike structures in the glomerular basement membrane, and these structures accumulated in the mesangium and capillary subendothelium. By electron microscopy, 2 types of distinctive structure were found in glomerular lesions: vacuole structures and cross-striated, membranelike structures. The plasma oxidized phosphatidylcholine (oxPC) -modified low density lipoprotein (LDL) levels in LCAT-deficient subjects were significantly (P<0.01) higher than those in controls (1.30+/-0.82 versus 0.42+/-0.32 ng/5 microg LDL, respectively), and a significant (P<0.01) difference was observed even after adjustment for confounding factors by an analysis of covariance. The patient with the highest plasma oxPC-modified LDL had the most membranelike structures in the glomeruli and showed the greatest renal deterioration from a young age. In glomerular lesions, although there was an abundance of apoB and apoE, oil red O-positive lipids, macrophages, apoA1, and malondialdehyde were scarce. OxPC was found extracellularly in glomerular lesions, and although its distribution differed from that of apolipoproteins, it was quite similar to that of phospholipids. In conclusion, these results indicate that oxPC in plasma and glomeruli is distinctive for patients with LCAT deficiency. Therefore, oxPC may be a factor in the deterioration of kidneys in patients with familial LCAT deficiency.