Plasma lipids, lipoproteins and apolipoproteins in two kindreds of hypobetalipoproteinemia

A variant form of hypobetalipoproteinaemia associated with ataxia, hearing loss and retinitis pigmentosa

A six-year-old Japanese boy had ataxia, mental retardation, peripheral neuropathy, proximal myopathy, hearing loss, retinitis pigmentosa and deficiencies in apolipoprotein AI, B, CII and CIII. His clinical features except for hearing loss resembled those of abetalipoproteinaemia or symptomatic hypobetalipoproteinaemia, but his apolipoprotein abnormalities were distinct from these disorders. He had apolipoprotein B-100 with a normal molecular weight. Although most of his neurological manifestations were compatible with those of vitamin E deficiency, their early onset and the presence of hearing loss was unusual for that condition. There has been slight deterioration of ataxia during two years follow-up despite high-dose vitamin E supplementation. Other abnormalities in lipid metabolism might be associated with the neurological damage in this case.

Immunoluminometric assays for the quantification of apolipoproteins A-I, B, C-II, apolipoprotein(a) and lipoprotein(a)

Immunoluminometric assays were developed for apolipoproteins A-I, B, C-II (as the apolipoprotein C-II: apolipoprotein B complex), apolipoprotein(a) and lipoprotein(a). The assays were evaluated clinically and methodologically. The results for apolipoprotein A-I, apolipoprotein B and lipoprotein(a) were compared with those obtained by turbidimetric assays. No comparison was possible for apolipoprotein C-II. Sample predilution was necessary for apolipoprotein A-I, apolipoprotein B, apolipoprotein(a) and lipoprotein(a). Not all antibody combinations gave rise to assays with acceptable recovery rates. This was especially the case for lipoprotein(a). These assays for apolipoprotein(a) and lipoprotein(a) had relatively low detection limit (< 5 mg/l) and measuring ranges up to 800 mg/l (using a 1:10 sample dilution), and were suitable for routine use, especially for longer series. Assay times were all less than 3 h, each assay using the streptavidin-biotin technique and being based on a coated-ball technology. The median intra-assay coefficients of variation for all assays lay between 2.9 and 5.9% in the range of interest, expressed in terms of precision profiles. Inter-assay (im)precision lay between 6.2 and 12.2%, calculated in the accepted way. Correlations between turbidimetric and immunoluminometric assays for apolipoprotein A-I and apolipoprotein B were statistically acceptable, although the correlation coefficients were mediocre (apolipoprotein A-I - r = 0.65, apolipoprotein B - r = 0.83) and the slope of the regression line differed from unity. This was most probably due to standardisation and differences in assay design (one-site competitive versus two-site immunometric assays).(ABSTRACT TRUNCATED AT 250 WORDS)

Receptor-dependent and -independent catabolism of low-density lipoprotein in a kindred with familial hypobetalipoproteinemia

Three affected members of a kindred with asymptomatic hypobetalipoproteinemia (HBL) were injected intravenously with 125I-labeled native low-density lipoproteins (LDL) and 131I-labeled cyclohexanedione (CHD)-treated LDL. Plasma and urine radioactivity data were collected for 15 days at regular intervals. A compartmental model using the SAAM program was built to fit simultaneously 125I and 131I plasma radioactivity decay and urine excretion data. This model allows precise calculation of the kinetic parameters of both receptor-independent (NR) and receptor-dependent (R) pathways. Compared with normal subjects, HBL patients show a 90% increased fractional catabolic rate (FCR) of LDL by both routes, more marked for the R pathway (215% increase), and an approximately 50% reduced production rate (PR). Structural analysis did not show significant abnormalities of apolipoprotein (apo) B in HBL patients compared with normal. These data suggest that the very reduced, LDL-apo B plasma levels result from a combination of two processes: (1) an increased activity of all catabolic routes, and (2) a reduced "synthesis" rate. The latter may result from a decreased conversion of very-low-density lipoprotein (VLDL) to LDL secondary to an increased direct removal of large VLDL, suggested by apo C-II and C-III turnover studies previously reported.

Apolipoprotein C-II and C-III metabolism in a kindred of familial hypobetalipoproteinemia

Three affected members of a kindred with asymptomatic hypobetalipoproteinemia (HBL) showed low levels of triglycerides, low-density lipoprotein (LDL)-cholesterol, and apolipoproteins (apo) B, C-II, and C-III. Turnover of iodine-labeled apo C-II and apo C-III associated in vitro to plasma lipoproteins was studied after intravenous injection. Radioactivity in plasma and lipoproteins (95% recovered in high-density lipoprotein [HDL] density range) and in 24-hour urine samples was observed for 16 days. A parallelism of the slowest slopes of plasma decay curves was observed between apo C-II and apo C-III, indicating a partial common catabolic route. Urine/plasma radioactivity ratio (U/P) varied with time, suggesting heterogeneity of metabolic pathways. A new compartmental model using the SAAM program was built, not only fitting simultaneously plasma and urine data, but also taking into account the partial common metabolism of lipoprotein particles (LP) containing apo C-II and apo C-III. The low apo C-II and C-III plasma concentrations observed in HBL compared with normal resulted from both an increased catabolism and a reduced synthesis, these changes being more marked for apo C-III. The modifications in the rate constants of the different pathways calculated from the new model are in favor of an increased direct removal of particles following the fast pathway, likely in the very-low-density lipoprotein (VLDL) density range.