Studies on high density lipoproteins in fish eye disease

A kindred with fish eye disease, corneal opacities, marked high-density lipoprotein deficiency, and statin therapy

A kindred affected with fish eye disease (FED) from Oklahoma is reported. Two probands with corneal opacification had mean levels of high-density lipoprotein (HDL) cholesterol (C), apolipoprotein (apo) A-I, and apoA-I in very large alpha-1 HDL particles that were 9%, 17%, and 5% of normal, whereas their parents and 1 sibling had values that were 61%, 77%, and 72% of normal. The probands had no detectable lipoprotein-X, and had mean low-density lipoprotein cholesterol (LDL-C) and triglyceride levels that were elevated. Their mean lecithin cholesterol acyltransferase (LCAT) activities, cholesterol esterification rates, and free cholesterol levels were 8%, 42%, and 258% of normal, whereas their parents and 1 sibling had values that were 55%, 49%, and 114% of normal. The defect was due to 1 common variant in the LCAT gene in exon 1: c101t causing a proline34leucine substitution and a novel mutation c1177t causing a threonine37methionine substitution, with the former variant being found in the father and 1 sibling, and the latter mutation being found in the mother, and both mutations being present in the 2 probands. FED is distinguished from familial LCAT deficiency (FLD) by the lack of anemia, splenomegaly, and renal insufficiency as well as normal or increased LDL-C. Both FLD and FED cases have marked HDL deficiency and corneal opacification, and FED cases may have premature coronary heart disease in contrast to FLD cases. Therapy, using presently available agents, in FED should be to optimize LDL-C levels, and 1 proband responded well to statin therapy. The investigational use of human recombinant LCAT as an enzyme source is ongoing.

In vitro normalization of cholesteryl ester content and particle size of fish eye disease high density lipoproteins

Isolated high density lipoprotein (HDL) from the two living fish eye disease patients have been incubated in vitro with autologous lipoprotein depleted plasma or with lipoprotein depleted plasma from domestic pig (Sus domesticus), with and without the presence of LCAT inhibitor for 24 hours at 0 and 37 degrees C. The lecithin:cholesterol acyltransferase (LCAT) activity in lipoprotein depleted pig plasma increased the abnormally low cholesteryl ester content of the fish eye disease HDL particles from about 20 to 100% and increased their exceptionally small mean particle size, probably by particle fusion, to a range which is representative of normal HDL3. Both esterification and particle enlargement were totally blocked by the LCAT inhibitor. Incubation of concentrated fish eye disease HDL with autologous lipoprotein depleted plasma for 24 hours at 37 degrees C resulted in a small increase in its cholesteryl ester percentage to 37%, without affecting the apparent HDL particle size. This finding confirms a deficiency of HDL lecithin:cholesterol acyltransferase activity (alpha-LCAT) in fish eye disease. The observed normalization of both HDL cholesteryl ester percentage and particle size by lipoprotein depleted pig plasma which contains virtually no cholesteryl ester transfer activity indicates that the latter is not a requisite for esterification of the free cholesterol of fish eye disease HDL.

Restriction enzyme analysis of the apolipoprotein A-I gene in fish eye disease and Tangier disease

Restriction enzyme analysis of the apolipoprotein A-I (apo A-I) gene was performed in two patients with fish eye disease and one with Tangier disease. Despite the marked deficiency of high density lipoprotein and concomitantly of apo A-I in these two conditions, no evidence was found for major deletions or insertions in the apo A-I gene.

Hypoalphalipoproteinemia resembling fish eye disease

A 16-year-old boy presented with bilateral arcus cornealis and markedly decreased plasma high density lipoprotein cholesterol. The plasma lipoprotein abnormalities, as well as decreased mass and activity of lecithin:cholesterol acyltransferase (LCAT), were similar to those described in patients with fish eye disease. Increased number of target cells and decreased osmotic fragility of the proband's erythrocytes were noted. The proband's father and one of his brothers showed intermediate plasma lipoprotein and LCAT alterations. The father's erythrocytes also showed abnormal osmotic fragility. The mother of the propositus had normal plasma lipoproteins and erythrocyte osmotic fragility, but her LCAT activity was also low. Many of these features suggest a disorder similar to fish eye disease which is clinically and biochemically distinct from other hypoalphalipoproteinemias.

Deficiency of hepatic lipase activity in post-heparin plasma in familial hyper-alpha-triglyceridemia

Hyper-alpha-triglyceridemia is a rare dyslipoproteinemia characterized by a pronounced increase in the concentration of triglycerides in the plasma high density lipoprotein (HDL) fraction. One case with this condition, an apparently healthy 61-year-old man, has been studied. Additional lipoprotein abnormalities were present, such as abnormally cholesterol-rich very low density lipoproteins (VLDL) with retarded electrophoretic mobility (beta-VLDL) and triglyceride enrichment of low density lipoproteins (LDL). The patient's plasma concentration of apolipoproteins A-I, A-II and B were normal and those of C-I, C-II, C-III and E were elevated. No abnormal forms of the soluble apolipoproteins of VLDL and high density lipoproteins (HDL) were found after analysis by isoelectric focusing. Lecithin:cholesterol acyltransferase activities, plasma cholesterol esterification rates and lipid transfer protein activities were normal. Post-heparin plasma activity of hepatic lipase was virtually absent and that of lipoprotein lipase was reduced by 50%. In plasma of this patient, HDL was almost exclusively present as large triglyceride-rich particles corresponding in size to particles of the HDL2 density fraction. The only brother of the patient also had hyper-alpha-triglyceridemia together with the other lipoprotein abnormalities described for the index case and deficiency of postheparin plasma activity of hepatic lipase. The findings presented below support the hypothesis that one primary function of hepatic lipase is associated with degradation of plasma HDL2. Deficiency of this enzyme activity thus causes accumulation of HDL2 in plasma leading to hyper-alpha-triglyceridemia. The results further suggest that the abnormal chemical and electrophoretic properties of VLDL and LDL in plasma from the patient, reminiscent of type III hyperlipoproteinemia, are secondary to the lack of the action of hepatic lipase on the HDL particles.

Paradoxical esterification of plasma cholesterol in fish eye disease

The activity of lecithin: cholesterol acyl transferase (LCAT), the enzyme which catalyses the esterification of human plasma cholesterol, has been measured by two independent methods in plasma from the two known living Swedish patients with fish eye disease. The enzyme activity was in both cases about 15% of that of normal plasma. Paradoxically, however, the percentage of plasma cholesterol which was esterified was almost normal in both patients. In addition, a normal spectrum of the fatty acids of the cholesteryl esters was present indicating a normal cholesterol esterification pathway in vivo. Incubation experiments in vitro of plasma from the two patients also yielded normal cholesterol esterification rates when measured by two different methods. These paradoxical results for cholesterol esterification are discussed on the basis of the present biochemical knowledge of fish eye disease and LCAT deficiency.

Evidence for deficiency of high density lipoprotein lecithin: cholesterol acyltransferase activity (alpha-LCAT) in fish eye disease

In a rare familial condition, fish eye disease, there is a low relative content of cholesteryl esters in the plasma high density lipoproteins (HDL) but a normal content of these lipids in the very low (VLDL) and low (LDL) density lipoproteins. Lecithin: cholesterol acyltransferase (LCAT) is the enzyme which mediates the esterification of free cholesterol in the plasma lipoproteins. In the present investigation, isolated HDL from our two fish eye disease patients were found to be excellent substrates during in vitro incubations with normal LCAT as present in lipoprotein depleted plasma from control subjects. Almost all free cholesterol of these HDL fractions became esterified and concomitantly the abnormally small fish eye disease HDL particles increased to a size in the range of that of normal HDL particles. Lipoprotein depleted plasma from fish eye disease, however, lacked the property of normal plasma to esterify the free cholesterol of HDL isolated from plasma of fish eye disease patients or control subjects. These results have led to the formulation of a new concept implying that two different LCAT activities exist in normal plasma. One of these activities, denoted alpha-LCAT, is specific for HDL (alpha-lipoproteins) and the other, beta-LCAT, is specific for VLDL-LDL (pre beta- and beta-lipoproteins). Fish eye disease according to this notion is classified as an alpha-LCAT deficiency in contrast to the classical LCAT deficiency which probably lacks both alpha- and beta-LCAT activities.

Different substrate specificities of plasma lecithin: cholesterol acyl transferase in fish eye disease and Tangier disease

Esterification of plasma free cholesterol is mediated by lecithin:cholesterol acyl transferase (LCAT). The free cholesterol of plasma high density lipoproteins (HDL) is considered to be the preferred substrate for LCAT. It therefore appeared as a paradox that plasma cholesterol esterification, both in vivo and in vitro, is normal in fish eye disease and Tangier disease, two familial conditions with extremely low plasma HDL levels. Fish eye disease plasma, however, was shown to have LCAT activity primarily acting on combined very low (VLDL) and low (LDL) density lipoproteins, denominated beta-LCAT, while it lacked LCAT activity esterifying HDL cholesterol (alpha-LCAT). Here we show that Tangier plasma, in contrast, has both alpha- and beta-LCAT. Thus, in both fish eye and Tangier diseases it is beta-LCAT that explains the apparent normal plasma cholesterol esterification. We also show that Tangier plasma, having alpha-LCAT activity, normalizes the low cholesteryl ester content as well as the abnormally small size of fish eye disease HDL particles during incubation.

Inhibitory effect of normal high density lipoproteins on lecithin:cholesterol acyltransferase activity in fish eye disease plasma

The lecithin:cholesterol acyltransferase (LCAT) activity of lipoprotein depleted normal and fish eye disease (FED) plasma was assayed in a modified Glomset-Wright incubation system where the enzyme was allowed to act on three different normal lipoprotein substrates consisting of an authentic mixture of very low (VLDL), low (LDL) and high (HDL) density lipoproteins to assay total LCAT activity, HDL to assay alpha-LCAT activity and combined VLDL and LDL to assay beta-LCAT activity, respectively. However, using normal plasma depleted of HDL, leaving its combined VLDL and LDL as enzyme substrate, resulted in a more than twofold increase in the LCAT activity of FED plasma from the two patients compared to the activity obtained with HDL present in the incubation mixture, indicating an inhibitory effect of HDL on the beta-LCAT activity present in FED plasma. This inhibitory effect of normal HDL could also be demonstrated by autoincubation of FED plasma mixed with isolated HDL2 or HDL3. Both these HDL subfractions had a pronounced inhibitory effect on the cholesteryl ester formation in FED plasma. The present study thus clearly demonstrates that normal HDL inhibits the beta-LCAT activity present in FED plasma, esterifying the free cholesterol of combined VLDL and LDL, derived from controls as well as from the two FED patients.

Evidence for the presence in human plasma of lecithin: cholesterol acyltransferase activity (beta-LCAT) specifically esterifying free cholesterol of combined pre-beta- and beta-lipoproteins. Studies of fish eye disease patients and control subjects

The present study was undertaken to test our hypothesis that two different lecithin: cholesterol acyltransferase (LCAT) activities exist in normal human plasma, one denoted alpha-LCAT esterifying the free cholesterol of high density lipoproteins (HDL) and the other denoted beta-LCAT acting on the free cholesterol of very low (VLDL) and low (LDL) density lipoproteins. Plasmas depleted of HDL were obtained by means of preparative ultracentrifugation. Incubation at 37 degrees C of these plasma fractions from control subjects and patients with fish eye disease resulted in esterification of the remaining free cholesterol of combined VLDL and LDL (pre-beta- and beta-lipoproteins) in the HDL depleted plasmas. The shapes of the cholesterol esterification rate curves were similar for whole and HDL depleted plasmas from both control subjects and fish eye disease patients. In crosswise mixed incubation experiments with isolated combined VLD and LDL and total lipoprotein depleted plasma from a control subject and a patient with fish eye disease, respectively, esterification of free cholesterol occurred. Incubation of isolated total lipoproteins in plasma from a patient with LCAT deficiency mixed with total lipoprotein depleted plasma from a fish eye disease patient as a source of LCAT caused cholesterol esterification but did not result in normalization of the LCAT deficiency HDL particles, while the amount of normal-sized LDL particles increased. The present results support the hypothesis that a beta-LCAT exists in normal human plasma.

Structural and functional properties of two mutants of lecithin-cholesterol acyltransferase (T123I and N228K)

Two naturally occurring mutants of human lecithin-cholesterol acyltransferase (LCAT), T123I and N228K, were expressed in COS-1 and Chinese hamster ovary cells, overproduced, and purified to homogeneity in order to study the structural and functional defects that lead to the LCAT deficiency phenotypes of these mutations. The mutants were expressed and secreted by transfected cells normally and had molecular weights and levels of glycosylation similar to wild type LCAT. The purified proteins (>98% purity) had almost indistinguishable structures and stabilities as determined by CD and fluorescence spectroscopy. Enzymatic activities and kinetic analysis of the pure enzyme forms showed that wild type LCAT and both mutants were reactive with the water-soluble substrate, p-nitrophenyl butyrate, indicating the presence of an intact core active site and catalytic triad. Both the T123I and N228K mutants had markedly depressed reactivity with reconstituted HDL (rHDL), but T123I retained activity with low density lipoprotein. To determine whether defective binding to rHDL was responsible for the low activity of both mutants with rHDL, the equilibrium binding constants were measured directly with isothermal titration calorimetry and surface plasmon resonance (SPR) methods. The results indicated that the affinities of the mutants for rHDL were only about 2-fold lower than the affinity of wild type LCAT (Kd = 2.3 x 10(-7) M). Together, the activity and equilibrium binding results suggest that the T123I mutant is defective in activation by apolipoprotein A-I, and the N228K mutant has impaired binding of lipid substrate to the active site. In addition, the kinetic binding rate constants determined by the SPR method indicate that normal LCAT dissociates from rHDL, on average, after one catalytic cycle.

Markedly accelerated catabolism of apolipoprotein A-II (ApoA-II) and high density lipoproteins containing ApoA-II in classic lecithin: cholesterol acyltransferase deficiency and fish-eye disease

Classic (complete) lecithin:cholesterol acyltransferase (LCAT) deficiency and Fish-eye disease (partial LCAT deficiency) are genetic syndromes associated with markedly decreased plasma levels of high density lipoprotein (HDL) cholesterol but not with an increased risk of atherosclerotic cardiovascular disease. We investigated the metabolism of the HDL apolipoproteins (apo) apoA-I and apoA-II in a total of five patients with LCAT deficiency, one with classic LCAT deficiency and four with Fish-eye disease. Plasma levels of apoA-II were decreased to a proportionately greater extent (23% of normal) than apoA-I (30% of normal). In addition, plasma concentrations of HDL particles containing both apoA-I and apoA-II (LpA-I:A-II) were much lower (18% of normal) than those of particles containing only apoA-I (LpA-I) (51% of normal). The metabolic basis for the low levels of apoA-II and LpA-I:A-II was investigated in all five patients using both exogenous radiotracer and endogenous stable isotope labeling techniques. The mean plasma residence time of apoA-I was decreased at 2.08 +/- 0.27 d (controls 4.74 +/- 0.65 days); however, the residence time of apoA-II was even shorter at 1.66 +/- 0.24 d (controls 5.25 +/- 0.61 d). In addition, the catabolism of apoA-I in LpA-I:A-II was substantially faster than that of apoA-I in LpA-I. In summary, genetic syndromes of either complete or partial LCAT deficiency result in low levels of HDL through preferential hypercatabolism of apoA-II and HDL particles containing apoA-II. Because LpA-I has been proposed to be more protective than LpA-I:A-II against atherosclerosis, this selective effect on the metabolism of LpA-I:A-II may provide a potential explanation why patients with classic LCAT deficiency and Fish-eye disease are not at increased risk for premature atherosclerosis despite markedly decreased levels of HDL cholesterol and apoA-I.

Two different allelic mutations in the lecithin-cholesterol acyltransferase gene associated with the fish eye syndrome. Lecithin-cholesterol acyltransferase (Thr123----Ile) and lecithin-cholesterol acyltransferase (Thr347----Met)

We have elucidated the genetic defect in a 66-yr-old patient with fish eye syndrome (FES) presenting with severe corneal opacities and hypoalphalipoproteinemia. The patient's plasma concentration of high density lipoprotein (HDL) cholesterol was reduced at 7.7 mg/dl (35.1-65.3 mg/dl in controls) and the HDL cholesteryl ester content was 31% (60-80% in controls); however, total plasma cholesteryl esters were similar to normal (60% of total cholesterol vs. a mean of 66% in controls). The patient's plasma cholesterol esterification rate was slightly reduced at 51 nmol/ml per h (control subjects: 61-106 nmol/ml per h), whereas lecithin-cholesterol acyltransferase (LCAT) activity, assayed using a HDL-like exogenous proteoliposome substrate, was virtually absent (0.9 nmol/ml per h vs. 25.1-27.9 nmol/ml per h in control subjects). DNA sequence analysis of the proband's LCAT gene revealed two separate C to T transitions resulting in the substitution of Thr123 with Ile and Thr347 with Met. The mutation at codon 347 created a new restriction site for the enzyme Nla III. Analysis of the patient's polymerase chain reaction-amplified DNA containing the region of the Thr347 mutation by digestion with Nla III confirmed that the proband is a compound heterozygote for both defects. The patient's daughter, who is asymptomatic despite a 50% reduction of LCAT activity, is heterozygous for the Thr123----Ile mutation. Our data indicate that the regions adjacent to Thr123 and Thr347 of LCAT may play an important role in HDL cholesterol esterification, suggesting that these regions may contain a portion of the LCAT binding domain(s) for HDL.

A 'Fish-eye disease' familial condition with massive corneal opacities and hypoalphalipoproteinaemia: clinical, biochemical and genetic features

A Caucasian family of mediterranean origin comprising a patient whose parents were first cousins, his wife and their three children, and his two sisters have been studied. The patient and his two daughters were afflicted with the same corneal opacities and hypoalphalipoproteinaemia. The disease was shown to be transmitted as a non-sex-linked recessive trait. The corneal opacities develop at the end of the second decade of life and consist of numerous minute greyish dots in the entire corneal stroma that give the cornea a misty appearance. Vision slowly deteriorated from 40 years of age. At about 50 years of age, except in one of the two daughters who showed Marfanoid syndrome, the three patients had good general health and no symptoms of atherosclerosis. Biochemical investigations showed hypoalphalipoproteinaemia (with a faint fast-moving HDL band on polyacrylamide gel gradient electrophoresis and small arcs of HDL2 and HDL3 of low mobility determined by agarose gel immunoelectrophoresis), low total cholesterol (3.5-4.9 mmol l-1), slightly decreased cholesteryl ester/total cholesterol ratio (0.52-0.63), extremely low HDL cholesterol (0.20-0.21 mmol l-1), mild hypertriglyceridaemia (1.94-3.80 mmol l-1), and striking deficiency in apo A-I and apo A-II (0.45-0.72, 0.08-0.16 g l-1, respectively). The esterification of HDL cholesterol was low while that of LDL and VLDL was nearly normal. Other laboratory values were normal. The HDL subspecies and major apolipoprotein isoforms have been studied to differentiate FED from Tangier disease, LCAT deficiency, as Apo A-I, A-II, C-II, C-III deficiencies and variants.(ABSTRACT TRUNCATED AT 250 WORDS)

Normalization of high density lipoprotein in fish eye disease plasma by purified normal human lecithin: cholesterol acyltransferase

Plasma from a patient with fish eye disease has been enriched with autologous high density lipoproteins (HDL) and supplemented with highly purified normal human plasma lecithin:cholesterol acyltransferase (LCAT). Incubation of such plasma at 37 C in vitro resulted in normalization of its low HDL cholesteryl ester percentage, from 23% to 79%, associated with a two-fold increase in both the cholesteryl ester and triglyceride contents of the HDL fraction, as compared to incubation experiments with absent or heat-inactivated purified normal LCAT. The normalization of the HDL cholesteryl ester percentage induced by incubation with purified normal LCAT also was accompanied by an increase in the size of the original fish eye disease HDL particles, which had a mean mass of 115 kd, to HDL particle populations with mean particle masses ranging from 130-220 kd, depending on the concentration of purified LCAT in the incubate. Both HDL cholesterol esterification and particle enlargement were abolished completely by the LCAT inhibitor DTNB and by heat inactivation of the purified normal LCAT. The results give further evidence that fish eye disease is an alpha-LCAT deficiency.

Familial LCAT deficiency and fish-eye disease

Familial LCAT deficiency is due to deficiency of plasma lecithin-cholesterol acyltransferase. The plasma is rich in free cholesterol and lecithin while cholesterol ester and lysolecithin levels are reduced. Analysis of the abnormal lipoproteins has helped our understanding of plasma lipid and lipoprotein metabolism in normals and in patients with liver disease. Proteinuria and anaemia are common and there is marked corneal lipid deposition. Eventually renal function deteriorates and dialysis and/or renal transplantation may be necessary. The human LCAT gene has been sequenced and been shown to be present on chromosomal segment 16q22-the region predicted on the basis of recombination studies as the site of the LCAT deficiency gene. The gene defect has been identified in some cases, but the mechanism remains unclear as the mutations were not in the region presumed to be the enzyme's active site. Only three cases of fish-eye disease have been described; all were elderly and had obvious corneal opacities. They had fasting hypertriglyceridaemia and increased VLDL. IDL and LDL were increased and were triglyceride rich. HDL, reduced by 90%, was mainly HDL3--with a high free and low ester cholesterol. LCAT activity in fish-eye plasma was normal but when measured in an exogenous substrate it was only 10-15% of normal. Fish-eye HDL is a substrate for purified LCAT, but fish-eye LCAT does not esterify free cholesterol of HDL (normal or fish-eye), although it esterifies free cholesterol of VLDL and LDL. It has been suggested that one type of LCAT activity acts on HDL (alpha-LCAT) and another on VLDL and LDL (beta-LCAT)--and that fish-eye disease is due to alpha-LCAT deficiency, and classical familial LCAT deficiency due to lack of both components.

Net lipid transfer between lipoproteins in fish-eye disease plasma supplemented with normal high density lipoproteins

Native fish-eye disease plasma, which is deficient of both high density lipoproteins (HDL) and lecithin-cholesterol acyltransferase activity (alpha-LCAT), processing the free cholesterol of these lipoproteins, has been supplemented with normal isolated HDL2 or HDL3 and incubated in vitro at 37 C. After incubation for 0, 7.5 and 24 hr the very low density (VLDL) and low density (LDL) lipoproteins as well as HDL were isolated, and their contents of triglycerides, phospholipids and free, esterified and total cholesterol were quantified. The resulting net mass transfer of the different lipids revealed a functioning transfer of cholesteryl esters and all other analyzed lipids between the lipoproteins, although no de novo esterification of the HDL cholesterol by LCAT in this plasma occurred. In accordance with previous findings there was a functioning esterification process of the free cholesterol of the combined VLDL and LDL of fish-eye disease plasma. The present reports make it reasonable to conclude that the lack of HDL cholesterol esterification in this disease is not a result of a deficiency of cholesteryl ester transfer or lipid transfer activities.

Bile acids and plasma high density lipoproteins: biliary lipid metabolism in fish eye disease

Cholesterol in plasma high density lipoproteins (HDL) has been proposed to serve as preferential precursor for bile acid biosynthesis in the liver. Furthermore, a negative relationship between plasma levels of HDL cholesterol and biliary saturation with cholesterol has been reported in healthy females. We have performed metabolic studies on a female patient with fish eye disease, a familial condition where plasma HDL levels are reduced by 90% and the concentration of plasma triglycerides is moderately increased. Both the total production of bile acids and the net steroid 'balance' (reflecting total body cholesterol synthesis) were within the range seen in normolipidaemic as well as in hypertriglyceridaemic females. Also the biliary lipid composition and cholesterol saturation of bile were normal. A qualitative abnormality in the bile acid pattern was observed, however, in that the ratio between the synthesis of cholic acid and chenodeoxycholic acid was reduced. It is concluded that a low HDL cholesterol level is not necessarily associated with quantitative abnormalities of biliary lipid metabolism. The abnormal bile acid synthesis ratio may reflect changes in the hepatic precursor pools of cholesterol as the consequence of HDL deficiency, however.

Electron microscopic structure of serum lipoproteins from patients with fish eye disease

The structure and composition of lipoprotein fractions from two patients with fish eye disease were examined. The composition of very low density lipoproteins (VLDL) was normal, although total mass was greatly elevated. The mean particle sizes of the VLDL were 44.6 +/- 22.2 and 42.8 +/- 19.8 nm for Patients 1 and 2, respectively. Intermediate density lipoprotein (IDL) concentrations in patients were elevated and contained increased triglyceride content; particle sizes for Patients 1 and 2 were 29.4 +/- 3.5 nm and 28.0 +/- 4.1 nm, respectively. In both patients, the triglyceride/cholesteryl ester ratio in LDL was approximately tenfold higher than in normal individuals; however, the LDL particles were somewhat smaller in diameter (23.5 +/- 3.0 nm for Patient 1 and 23.3 +/- 3.8 nm for Patient 2) than those of controls (25.8 +/- 3.0 nm and 24.9 +/- 3.4 nm). In both patients, large vesicular structures were occasionally encountered in the LDL region. The high density lipoprotein (HDL) fraction of fish eye disease patients showed the greatest abnormalities. Not only was the total HDL concentration extremely low (approximately 10% of control levels), but unesterified cholesterol was increased relative to cholesteryl ester. Particle morphology was heterogeneous; the major HDL species was a small spherical particle with a diameter of 7.6 nm. Discoidal particles with a thickness of 4.4 nm and diameters between 17.4 and 20.8 nm were also present, together with large (40-90 nm) vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)