Unmasking of Type III Hyperlipoproteinemia by Hypothyroidism: A Dramatic Illustration of Altered Lipoprotein Metabolism in a Postpartum Woman

ObjectiveTo illustrate the potential abnormalities in lipoprotein metabolism associated with type III hyperlipoproteinemia and the modulation of their clinical expression by thyroid hormone and estrogenic status.MethodsAn illustrative case, with associated clinical and laboratory data, is presented, and relevant clinical and pathophysiologic studies from the literature are reviewed.ResultsA 35-year-old woman, at 7 months after delivery of her first child, presented to her family physician with a complaint of painful eruptions on the palms of her hands. On evaluation, she was found to have new hypothyroidism and severe hypertriglyceridemia (> 1,569 mg/dL). Thyroxine replacement was initiated, and she was referred to the lipid clinic. When seen in the lipid clinic shortly thereafter, her triglyceride level had normalized, but her low-density lipoprotein (LDL) fraction was strikingly elevated (representing a combination of elevated intermediate-density lipoprotein and LDL cholesterol). On physical examination, palmar xanthomas were noted, suggestive of type III hyperlipoproteinemia. This diagnosis was further supported by homozygosity at the apolipoprotein E (apo E) gene locus for the apo E2 allele implicated in this condition. Ultimately, with attainment of euthyroidism in the subsequent weeks, the lipid profile normalized, with the LDL cholesterol concentration particularly reduced at 55 mg/dL.Conclusion: Clinical expression of type III hyperlipoproteinemia necessitates interaction between an underlying genetic defect of lipoprotein metabolism (apo E2 homozygosity) and a secondary metabolic insult such as, in the current case, hypothyroidism and possibly breast-feeding-mediated hypoestrogenemia. As such, in patients with type III hyperlipoproteinemia, it is essential to search for exacerbating factors, particularly because the amelioration of such factors may rectify the effects of the underlying dyslipidemia. (Endocr Pract. 2005;11:394-398)     

Presence of two forms of apolipoprotein B in patients with dyslipoproteinemia

Current information suggests that the major forms of the human B apolipoproteins, B-100 and B-48, are under separate genetic control and are synthesized by the liver and intestine, respectively. The apolipoprotein B composition of plasma lipoproteins has been determined in order to gain insight into the metabolic defects in patients with dyslipoproteinemias. Patients with type I and type V hyperlipoproteinemia can be separated into two groups based on apolipoprotein composition and triglyceride concentration. The first group had markedly elevated plasma triglycerides with B-48 in the 1.006 g/ml density fraction and only B-100 within IDL and LDL. The second group had plasma triglycerides less than 1200 mg % and only B-100 in all density fractions. Patients with type III hyperlipoproteinemia had B-48 in only the density less than 1.006 g/ml with B-100 in IDL and LDL; the type III hyperlipoproteinemic patient with apolipoprotein E deficiency, however, had B-48 in density less than 1.006 g/ml fraction, IDL, and LDL. Patients with type IIa, IIb, and IV hyperlipoproteinemia had only B-100 in all density fractions. These combined results are interpreted as indicating that B-48 is associated with triglyceride-rich lipoproteins synthesized by the intestine and that patients with phenotypes I, III, and V have defects in chylomicron remnant metabolism. In addition, in patients with types I and V hyperlipoproteinemia, mild hypertriglyceridemia appears to be associated with lipoprotein particles of liver origin.     

Apolipoprotein E3-Leiden. A new variant of human apolipoprotein E associated with familial type III hyperlipoproteinemia

Summary A variant of apolipoprotein E, denoted apo E3-Leiden, has been identified in a 41-year-old male suffering from type III hyperlipoproteinemia with xanthomatosis. Apo E3-Leiden focus in the E3 position. In contrast with normal apo E3, apo E3-Leiden is defective in binding to the low density lipoprotein (LDL) receptor and does not contain cysteine as evaluated by cysteamine treatment of very low density lipoprotein followed by isoelectric focusing and conventional protein staining and by amino acid analysis. On sodium dodecyl sulfate polyacrylamide gel electrophoresis, apo E3-Leiden displays an electrophoretic mobility intermediate to that of normal apo E3 and apo E2 (Arg₁₅₈Cys). The mother and four siblings of the proband also have apo E3-Leiden and hyperlipoproteinemia type III; three of them with xanthomatosis. Two siblings do not show apo E3-Leiden in their VLDL fraction and do not have hyperlipoproteinemia type III. In the VLDL fractions of all affected family members only the presence of apo E3-Leiden could be detected after cysteamine treatment and isoelectric focusing followed by conventional protein staining. However, isoelectric focusing of cysteaminetreated sera followed by immunoblotting, using anti-apo E antiserum as first antiserum, demonstrates the presence of low amounts of normal apo E3 in addition to apo E3-Leiden in serum of the affected family members. These results indicate that all affected family members are heterozygotes E3/E3-Leiden and suggest that in this family type III hyperlipoproteinemia is transmitted as a dominant trait.     

Human apolipoprotein E isoprotein subclasses are genetically determined.

In a recent communication, we showed that human very low density lipoprotein (VLDL) apolipoprotein E (Apo E) from different individuals appears upon two-dimensional gel electrophoretic analysis in either one of two complex patterns. These have been designated class alpha and class beta. Mixing of VLDL from different subjects revealed that not all alpha or beta apo E patterns were the same. In this manner, we identified three subclasses of class alpha (alpha II, alpha III, and alpha IV) and three subclasses of class beta (beta II, beta III, and beta IV). We report here the results of family studies that reveal that the subclasses (alpha II, alph III, and alpha IV and beta II, beta III, and beta IV) of apo E are determined at a single genetic locus with three common alleles, epsilon II, epsilon III, and epsilon IV. The class beta phenotypes (beta II, beta III, and beta IV) represent homozygosity for two identical apo E alleles (epsilon). In contrast, class alpha phenotypes (alpha II, alpha III, and alpha IV) represent heterozygosity for two different apo E alleles. The apo E subclasses and their corresponding genotypes are as follows: beta II = epsilon II/epsilon II; beta III = epsilon III; beta IV = epsilon IV/epsilon IV; alpha II = epsilon II/epsilon III; alpha III = epsilon III/epsilon IV; and alpha IV = epsilon II/epsilon IV. To estimate the frequencies of the apo E alleles in the general population, apo E subclasses were then investigated in 61 unrelated volunteers and the results were: beta II = 1 (2%), beta III = 30 (49%), alpha II = 9 (15%, alpha III = 13 (31%), and alpha IV = 2 (3%). Utilizing the frequencies of these phenotypes, the gene frequencies were calculated to be epsilon II = 11%, epsilon III = 72%, and epsilon IV = 17%. In addition, apo E subclasses were studied in a clinic for individuals with plasma lipid disorders and the apo E subclass beta IV was found to be associated with type III hyperlipoproteinemia. There was no association of any apo E subclass with type II, type IV, or type VI hyperlipoproteinemia or plasma HDL cholesterol levels. This study explains the genetic basis for the common variation in a human plasma protein, apo E. Since the apo E subclass beta IV is associated with type III hyperlipoproteinemia, a disease characterized by xanthomatosis and premature atherosclerosis, understanding the genetic basis of the apo E subclasses should provide insight into the genetics of type III hyperlipoproteinemia.     

The functional characteristics of a human apolipoprotein E variant (cysteine at residue 142) may explain its association with dominant expression of type III hyperlipoproteinemia.

Type III hyperlipoproteinemia typically is associated with homozygosity for apolipoprotein (apo) E2(Arg158----Cys). Dominant expression of type III hyperlipoproteinemia associated with apoE phenotype E3/3 is caused by heterozygosity for a human apoE variant, apoE3(Cys112----Arg, Arg142----Cys). However, this apoE3 variant was not separable from the normal apoE3 in these patients' plasma because the two proteins have identical amino acid composition, charge, and molecular weight. Therefore, to determine the functional characteristics of this protein, we used recombinant DNA techniques to produce this apoE variant in bacteria. We also produced a non-naturally occurring variant, apoE(Arg142----Cys), that had only the cysteine substituted at residue 142. These two apoE variants were purified from cell lysates of the transfected Escherichia coli by ultracentrifugal flotation in the presence of phospholipid, by gel filtration chromatography, and by heparin-Sepharose chromatography. Both Cys142 apoE variants bound to lipoprotein receptors on human fibroblasts with only about 20% of normal binding activity. Therefore, cysteine at residue 142, not arginine at residue 112, is responsible for the decreased receptor binding activity of the variants. Cysteamine treatment and removal of the carboxyl-terminal domain had little effect on the binding activity, whereas both modulate the receptor binding activity of apoE2(Arg158----Cys). The mutation at residue 142 decreased the binding activity of apoE to both heparin and the monoclonal antibody 1D7 (this antibody inhibits receptor binding of apoE), whereas apoE2(Arg158----Cys), which is associated with recessive expression of type III hyperlipoproteinemia, binds normally to both. The Arg112, Cys142 variant predominantes 3:1 over normal apoE3 in the very low density lipoproteins of plasma from an affected subject, as assessed by differential reactivity with the antibody 1D7. The unique combination of functional properties of the Arg112, Cys142 variant provides a possible explanation for its association with dominant expression of type III hyperlipoproteinemia.     

Anti-kappa elastin antibody titer in the sera of patients with hyperlipoproteinemia type II, III and IV]

Titre of antibodies against elastin degradation product (kappa-elastin) was measured in patients with atherogenic types of hyperlipoproteinemia. The hemagglutination technique was used. A significant decrease in titres of the tested antibodies was found. It was the most prominent in IIa, III and IIb types of hyperlipoproteinemia and rather mild in IV type. The authors attempted to explain causes of antibodies titres decrease in tested patients and relate their results with those of other authors.     

Apolipoprotein E Bethesda. Isolation and partial characterization of a variant of human apolipoprotein E isolated from very low density lipoproteins

A variant of apolipoprotein E, denoted E Bethesda, has been identified in the plasma of a 72-year-old woman with type III hyperlipoproteinemia. An offspring of the proband also has this variant and type III hyperlipoproteinemia. Apolipoprotein E Bethesda was isolated by preparative isoelectrofocusing followed by preparative SDS-polyacrylamide gel electrophoresis from the very low density lipoproteins of the proband's son. The purity and the identity of the preparation were analyzed by analytical SDS-polyacrylamide gel electrophoresis, two-dimensional gel electrophoresis and by immunochemical analysis. Apolipoprotein E Bethesda migrates in the E 1 position and its electrophoretic mobility is not affected by neuraminidase treatment. The protein is shifted to the E3 position after cysteamine treatment. The amino acid composition revealed the presence of two cysteine residues. These data support the concept that the apolipoprotein E Bethesda allele is derived from a mutation of the E2 or E2* allele.     

Inactivation of the murine Transferrin Receptor 2 gene using the Cre recombinase: loxP system

Transferrin Receptor 2 (TfR2) is a key molecule involved in the regulation of iron homeostasis. Mutations in TfR2 lead to type 3 hemochromatosis in humans. We have developed mice with a targeted deletion of TfR2. The Cre-recombinase:loxP system used to create the mice allows both full deletion and tissue-specific deletion of TfR2. The development of these mice will provide new models for type 3 hemochromatosis and assist in determining the role of TfR2 in iron metabolism.     

Plasma ferritin concentrations: their clinical significance and relevance to patient care.

In healthy persons the plasma ferritin concentration is a sensitive index of the size of body iron stores. It has been successfully applied to large-scale surveys of the iron status of populations. It has also proved useful in the assessment of clinical disorders of iron metabolism. A low plasma ferritin level has a high predictive value for the diagnosis of uncomplicated iron deficiency anemia. It is of less value, however, in anemia associated with infection, chronic inflammatory disorders, liver disease and malignant hematologic diseases, for which a low level indicates iron deficiency and a high level excludes it, but intermediate levels are not diagnostic. Measuring the plasma ferritin concentration is also useful for the detection of excess body iron, particularly in idiopathic hemochromatosis, but again it lacks specificity in the presence of active hepatocellular disease. If iron overload is suspected in these circumstances determination of the iron content of a percutaneous liver biopsy specimen is required. In families with idiopathic hemochromatosis the combined determination of the plasma ferritin concentration and the transferrin saturation is a sufficient screen to identify affected relatives; however, estimation of the hepatic iron concentration is required to establish the diagnosis.     

Apolipoprotein E phenotypes in patients with myocardial infarction

Summary The frequencies of genetic apo E isoforms E2, E3 and E4 were determined in 523 patients with myocardial infarction and compared to those in a control group (1031 blood donors). A significant difference in the frequency of apo E4 was noted between patients and controls (0.05> P>0.025). No differences in the frequencies of isoforms E3 and E2 were observed. In particular, there was no significant difference between the two groups in the frequency of apo E2 homozygosity. a condition that is associated with type III hyperlipoproteinemia. However, all E2 homozygote survivors of myocardial infarction had hyperlipoproteinemia type III (cholesterol 269±29 mg/dl; triglyceride 419±150 mg/dl; age 54±14 years; N=5). On the contrary, E2 homozygote controls (all apo E-2/2 blood donors and their apo E-2/2 relatives who were from the same age range as the patients) had primary dysbetalipoproteinemia but normal or subnormal plasma cholesterol concentrations (cholesterol 184±28 mg/dl; triglyceride 151±52 mg/dl; age 56±13 years; N=11). This indicates that E2 homozygotes with hyperlipoproteinemia type III who occur rarely in the population but comprise about 1% of myocardial infarction patients have a markedly increase risk for coronary atherosclerosis, whereas the risk for E2 homozygotes with normal or subnormal plasma cholesterol (=primary dysbetalipoproteinemia) may be considerably lower than for the general population. The data illustrate the complex relationship between apo E genes, lipid levels, and risk for atherosclerosis.     

Apolipoprotein E-1Harrisburg: a new variant of apolipoprotein E dominantly associated with type III hyperlipoproteinemia

Apolipoprotein E (apoE) is important in the modulation of the catabolism of chylomicron and very low density lipoprotein (VLDL) remnants. ApoE has three major genetically determined isoproteins in plasma, designated apoE-2, apoE-3 and apoE-4, with homozygosity for the allele coding for apoE-2 being associated with dysbetalipoproteinemia or type III hyperlipoproteinemia (HLP). We describe a new variant of apoE, apoE-1Harrisburg, which is, in contrast to apoE-2, dominantly associated with type III HLP. Five of twelve members of the affected kindred are heterozygous for the mutant form of apoE, and four of the five have type III HLP, while the fifth member has dysbetalipoproteinemia on diet therapy. Neuraminidase digestion, which removes charged sialic acid residues, did not alter the electrophoretic position of the apoE-1Harrisburg isoprotein, indicating that the altered charge of apoE-1Harrisburg was not due to sialic acid addition to the apolipoprotein. Cysteamine modification, which adds a positively charged group to cysteine, resulted in a shift of apoE-1Harrisburg from the E-1 to the E-2 isoform position, indicating that there is one cysteine in apoE-1Harrisburg as is the case for apoE-3. These results are consistent with apoE-1Harrisburg originating in the allele for apoE-3 with the mutation leading to a negative two-unit charge shift. The definitive identification of a kindred with an apoE variant, apoE-1Harrisburg, dominantly associated with dysbetalipoproteinemia and type III HLP provides a unique opportunity to gain important insights into the structure-function requirements of the E apolipoprotein as well as the mechanisms by which apoE modulates lipoprotein metabolism.     

Influence of lipid metabolism disorders on venous thrombosis risk

Background: To investigate the influence of lipid metabolism disorders on the risk of deep vein thrombosis. Methods: A total of 200 subjects participated in the study, 100 of whom experienced DVT with or without PTE, and 100 healthy subjects representing the control group. We classified patients and controls in terms of serum concentrations of chylomicrons, LDL, IDL, VLDL, and HDL particles, as those with or without hyperlipoproteinemia and in terms of serum Lp (a) lipoprotein levels, as those with hyperLp (a) lipoproteinemia (serum Lp (a) values >0.3 g/L) and those without hyperLp (a) lipoproteinemia (serum Lp (a) values <0.3 g/L). Based on the modified and supplemented Fredrickson classification, participants with verified existences of hyperlipoproteinemia were classified into subgroups based on the type of hyperlipoproteinemia. Unconditional logistic regression was used to calculate ORs with 95% CIS as a measure of the relative risks for venous thrombosis in participants with hyperlipoproteinemia compared with those without hyperlipoproteinemia. The analysis was adjusted for all potential confounders (age, sex, obesity) related to the functionality of the lipid metabolism, and at the same time, may have an impact on the risk of venous thrombosis. Results: The results of the comparison of the mean values of individual lipid status parameters between the patient group and the control group clearly indicate higher concentrations of total cholesterol (5.93 mmol/L vs. 5.52 mmol/L), total triglycerides (1.58 mmol/L vs. 1.50 mmol/L), and LDL-cholesterol (3.83 mmol/L vs. 3.44 mmol/L) in the patient group relative to the control group, with a statistically significant difference observed only in the case of LDL-cholesterol concentrations. We have found that type IIa hyperlipoproteinemia is associated with a nearly double increased risk for deep vein thrombosis (OR 1.99; Cl 1.01-3.90), while type IIb, IV, or hyperLp (a) lipoproteinemia did not influence the risk (OR 1.22; 95% Cl 0.79-1.84; OR 0.89; 95% Cl 0.52-1.54 OR 1.85; 95% CI 0.84-4.04). Conclusions: Hypercholesterolemia doubles the risk of deep vein thrombosis development.     

A study of the hypolipidemic effect of estrogen in type III hyperlipoproteinemia

Ethinylestradiol (1 microgram/kg/day during 15 days) resulted in a gradual decrease of serum cholesterol, serum triglycerides (TG), very low density lipoprotein (VLDL) cholesterol and VLDL-TG in 2 postmenopausal women and 2 men with type III hyperlipoproteinemia (HLP). The turnover rate of VLDL-TG did not change. These findings contrast with previous observations in normal subjects and patients with type IV HLP. Thus, the catabolism of VLDL and VLDL-remnants increased during treatment with estrogen in type III HLP, probably by direct degradation of VLDL-remnants because in the initial days of treatment no increase of LDL-cholesterol was observed.     

Apolipoprotein E2-Dunedin (228 Arg replaced by Cys): an apolipoprotein E2 variant with normal receptor-binding activity

Homozygosity for the apolipoprotein (apo) E variant apoE2(158 Arg----Cys) invariably gives rise to dysbetalipoproteinemia, and when associated with obesity or a gene for hyperlipidemia, results in type III hyperlipoproteinemia. The association of the E2/2 phenotype with type IV/V hyperlipoproteinemia rather than type III hyperlipoproteinemia in identical twin brothers led us to investigate the primary structure of their apoE. Lipoprotein electrophoresis on agarose gels confirmed the presence of increased very low density lipoproteins (VLDL) and chylomicrons but little, if any, beta-VLDL, indicating that these subjects did not have dysbetalipoproteinemia. When the apoE from these twins was subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis on a system that can distinguish apoE2(158 Arg----Cys) from all other known apoE variants, it gave rise to two components. One had the unique mobility of apoE2(158 Arg----Cys), and one migrated in the position of the other variants of apoE (and normal apoE3), indicating that the brothers were heterozygous for apoE2(158 Arg----Cys) and a second apoE2 isoform. Cysteamine modification and isoelectric focusing showed that, like apoE2(158 Arg----Cys), the second apoE2 isoform also contained two cysteine residues. The structural mutation in the second apoE2 isoform was determined by peptide sequencing. Like normal apoE3, this variant had arginine at position 158, but differed from apoE3 by the substitution of cysteine for arginine at position 228. Total apoE isolated from the brothers had the same receptor-binding activity in a competitive binding assay as a 1:1 mixture of normal apoE3 and apoE2(158 Arg----Cys).(ABSTRACT TRUNCATED AT 250 WORDS)     

Idiopathic hemochromatosis and chromosomal damage.

Spontaneous and radiation-induced chromosome damage in cultured lymphocytes was examined in a pilot study of 11 patients with idiopathic hemochromatosis and matched controls. Increased frequencies of chromosome breaks were found in the patients, both spontaneously and after exposure to ionizing radiation, but the differences between patients and controls were not statistically significant (p greater than 0.05) when individual data were analyzed. When pooled (group) data for patients and controls were compared, significant increases in spontaneous and radiation-induced chromosome breaks were found among the patients. The results suggest that iron overload may lead to chromosome damage in idiopathic hemochromatosis.     

Variable expression of hypercholesterolemia in Apolipoprotein E2* (Arg136 --> Cys) heterozygotes

In the process of population screening for apo E gene polymorphism with the PCR and subsequent restriction analysis, we identified a female who demonstrated heterozygosity for an unusual restriction fragment caused by the loss of a CfoI restriction site. Sequence analysis of the apo E gene was performed and a carrier of the mutant allele with C --> T substitution at cDNA position 3817 was identified, which caused an Arg136 --> Cys change. The first-line relatives have been screened for this rare mutation with PCR and restriction analysis of PCR products. The complete lipoprotein parameters have been determined in the probands family. In the family, only one child had the same mutant allele as his mother had. The proband (7.49 mmol/l) with her siblings had hypercholesterolemia and a high body mass index (BMI 31.6 kg/m2). By contrast, her son had a normal lipid spectrum with normal BMI. We described the mutation apo E2* (Arg136 --> Cys) in a family with elevated lipid levels, but there was no confirmation of the connection between this mutation and type III hyperlipoproteinemia or hyperlipoproteinemia at all. In the case of this mutation, other factors (mainly genetic) are important for the development of lipid metabolism disorders.     

Iron-independent specific protein expression pattern in the liver of HFE-deficient mice

Hereditary hemochromatosis type I is an autosomal-recessive iron overload disease associated with a mutation in HFE gene. The most common mutation, C282Y, disrupts the disulfide bond necessary for the association of HFE with beta-2-microglobulin and abrogates cell surface HFE expression. HFE-deficient mice develop iron overload indicating a central role of the protein in the pathogenesis of hereditary hemochromatosis type I. However, despite significant effort, the role of the HFE protein in iron metabolism is still unknown. To shed a light on the molecular mechanism of HFE-related hemochromatosis we studied protein expression changes elicited by HFE-deficiency in the liver which is the organ critical for the regulation of iron metabolism. We undertook a proteomic study comparing protein expression in the liver of HFE deficient mice with control animals. We compared HFE-deficient animals with control animals with identical iron levels obtained by dietary treatment to identify changes specific to HFE deficiency rather than iron loading. We found 11 proteins that were differentially expressed in the HFE-deficient liver using two-dimensional electrophoresis and mass spectrometry identification. Of particular interest were urinary proteins 1, 2 and 6, glutathione-S-transferase P1, selenium binding protein 2, sarcosine dehydrogenase and thioredoxin-like protein 2. Our data suggest possible involvement of lipocalins, TNF-alpha signaling and PPAR alpha regulatory pathway in the pathogenesis of hereditary hemochromatosis and suggest future targeted research addressing the roles of the identified candidate genes in the molecular mechanism of hereditary hemochromatosis.     

Idiopathic hemochromatosis: demonstration of homozygous-heterozygous mating by HLA typing of families

Summary In five families with idiopathic (hereditary) hemochromatosis, clinical and biochemical expression of the disease occurred in offspring of probands, suggesting an autosomal dominant mode of inheritance. However, HLA typing of subjects indicated that a homozygous-heterozygous mating almost certainly had occurred in four of the five families, resulting in homozygous offspring. Thus, in these families inheritance of the hemochromatosis trait was best explained in terms of an autosomal recessive or intermediate mode of inheritance. This study demonstrates the value of HLA typing in identifying homozygous-heterozygous matings in hemochromatosis families.     

Effect of compositional modification of coffee on certain indices of lipid metabolism in healthy volunteers and patients with hyperlipoproteinemia]

An effect of a 14-day drinking of coffee on some blood serum indices of lipid metabolism was investigated in 20 healthy volunteers and 20 patients with hyper lipoproteinemia (type IIb). The study was carried out in two subgroups: healthy volunteers or patients with hyperlipoproteinemia assigned to the first subgroup drank ordinary coffee and patients assigned to the second subgroup drank coffee deprived of irritant substances (4 glasses daily). It was found that ordinary coffee significantly increased total serum cholesterol and decreased serum HDL-cholesterol in healthy volunteers. Such effects were not seen in subgroup drinking coffee deprived of irritant substances. More significant increase in serum total cholesterol and decrease in serum HDL-cholesterol were found in patients with hyperlipoproteinemia. Drinking of modified coffee does not cause any significant changes in serum lipid metabolism. The authors concluded that drinking of the ordinary coffee should be restricted in patients with hyperlipoproteinemia and use of coffee deprived of irritant substances might be recommended to patients with this disease.     

Relation of cardiovascular risk factors to atherosclerosis in type III hyperlipoproteinemia

The familial lipoprotein disorder type III hyperlipoproteinemia (HPL) carries a marked increase in the risk of accelerated and premature atherosclerosis, but there is considerable variation among affected individuals in susceptibility to cardiovascular disease (CVD). We studied the influence of independent risk factors for atherosclerosis in 67 patients with clinically overt type III HPL and homozygosity for apolipoprotein (apo) E2. Among the different risk factors (lipid and lipoprotein levels, age, sex, body mass index, smoking status, hypertension, and diabetes mellitus) there was only a statistically significant difference in age between 25 patients with atherosclerosis and 42 patients without atherosclerosis. Serum lipoprotein (a), [Lp, (a)], levels were 30.6% higher in the atherosclerosis group, but this was not statistically significant. We conclude that (in contrast to familial hypercholesterolemia) elevated Lp (a) concentrations may not be regarded as a component of the clinical syndrome of type III HPL.