Tangier disease is a rare familial disorder characterized by extremely low levels of apolipoprotein A-I (apoA-I) and high density lipoproteins (HDL). In normal subjects, proapoA-I is secreted into plasma and converted to mature apoA-I by the cleavage of the amino-terminal six amino acids with the major isoprotein in plasma being mature apoA-I. In contrast, in Tangier disease there is a marked relative increase of proapoA-I as compared with mature apoA-I. ProapoA-I and mature apoA-I were isolated from normal and Tangier disease subjects, radiolabeled, and autologous apoA-I isoproteins injected into normal and Tangier subjects. The in vivo catabolism and conversion of proapoA-I and mature apoA-I in normal and Tangier disease subjects were quantitated. A comparison of the rate of catabolism of apoA-I isoproteins from plasma revealed a significantly faster rate of catabolism of both isoproteins of apoA-I in Tangier subjects when compared with normal subjects. The fractional conversion rate of proapoAI to mature apoA-I was 3.9 d' in normal subjects and 3.6 d ' in Tangier subjects. The results indicate that (a) apoA-I enters plasma as the pro isoprotein in both normal and Tangier subjects, (b) Tangier disease subjects have a normal fractional rate of conversion of proapoA-I to mature apoA-I, (c) proapoA-I is catabolized at the same rate as mature apoA-I in Tangier subjects, and (d) Tangier subjects catabolize both pro and mature apoA-I at a much greater rate than do normal subjects. Therefore, the relative increase in proapoA-I in Tangier disease is due to a marked decrease in mature apoA-I resulting from rapid catabolism of both pro-and mature apoA-I and not to defective conversion of proapoA-I to mature apoA-I.

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To determine the impact of long-term immunosuppression on serum lipids in stable renal graft recipients we measured serum lipids and apolipoprotein B concentrations in 20 patients receiving therapy with cyclosporin (CsA) and low-dose prednisolone (CsA/P) and in 18 patients on therapy with azathioprine and maintenance steroids (Aza/P). The patients were matched for age, body mass index, primary renal disease and dose of prednisolone, but not for the duration in transplantation and serum creatinine concentration. Triglyceride concentrations were significantly higher in the CsA/P group than in Aza/P-treated patients: 2.62 +/- 0.35 vs 1.62 +/- 0.23 mmol/l (P less than 0.05). Similarly, total cholesterol (C) levels were significantly more elevated in the CsA/P recipients than in the other group: 7.44 +/- 0.32 vs 5.84 +/- 0.25 (P less than 0.02). CsA/P patients had higher serum levels of LDL-C (4.79 +/- 0.20 vs 3.43 +/- 0.19 mmol/l (P less than 0.001) and apolipoprotein B concentrations (191 +/- 13 vs 128 +/- 9 mg/dl: P less than 0.001). CsA/P and Aza/P recipients had similar concentrations of HDL-C (1.73 +/- 0.13 vs 1.52 +/- 0.09 mmol/l: NS). We conclude that in stable renal graft recipients with good transplant function long-term immunosuppression with CsA/P is associated with a more atherogenic lipid status than therapy with Aza/P.

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 Thr23 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 Thr, 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. (J.