Changes in the serum lipoprotein pattern following dietary treatment, the genetic relationship and the postheparin lipolytic activity (PHLA) were investigated in patients with hyperlipoproteinemia associated with the presence of an intermediate lipoprotein.
In these patients the serum lipoprotein pattern observed on polyacrylamide gel disc electrophoresis (PAGE), exhibited a “Mid-band” or the broad band ranging between pre-β- and β-lipoproteins. But the major peak of the mid-band was located at different positions for each subject, in some cases by the side of pre-β- and others by the side of β- lipoprotein. Most of the intermediate lipoproteins showing the mid-band on PAGE in these patients were detected as the intermediate lipoprotein of the density range 1.006-1.019 by means of the ultra-centrifugal separation and the estimation of the lipid composition.
In M family with hypertriglyceridemia, the propositus (G. M.) had an extremely high serum triglyceride level, above 2, 500mg/d
l on a regular or high-fat diet. At this time the lipoprotein electrophoresis demonstrated a pattern of type V hyper-lipoproteinemia. While he received a low-fat diet (fat<15g per day), his serum triglyceride concentration was reduced to 500mg/d
l and the serum lipoprotein pattern showed an accumulation of intermediate lipoprotein with a disappearance of chylomicron. G. M. and his wife were first cousins. One of their daughters (F. M.) suffered from abdominal pain and diarrhea with “fat-induced” hypertriglyceridemia and also showed an intermediate lipoprotein. Another daughter died of acute pancreatitis with severe hypertriglyceridemia more than 2, 000mg/d
l. Both G. M. and F. M. had a deficiency of PHLA both for hepatic triglyceride lipase (H-TGL) and extrahepatic lipoprotein lipase (LPL) activities, so that the M family was considered to be affected with a subtype of familial lipoprotein lipase deficiency.
S family had three siblings with hyperlipoproteinemia and two of them had tendon xanthomas. The propositus (H. S.) was admitted with acute myocardial infarction and her lipoprotein pattern had intermediate lipoprotein by the side of β-lipoprotein. All of the family members with hyperlipoproteinemia had similar lipoprotein patterns. Following a calorie-restricted diet, H. S.' serum triglyceride concentration was reduced from 245mg/d
l to 96mg/d
l and her lipoprotein pattern turned to a typical type IIa phenotype with the disappearance of the intermediate lipoprotein. Thus, the S family was characterized essentially by familial hypercholesterolemia.
In most of the other subjects with hyperlipoproteinemia in this study, H-TGL was below normal but not severely deficient. Only one of these cases (K. O.) that was defined as typical “broad-β disease” by clinical symptoms and the chemical index showed a markedly reduced H-TGL. One of the other cases, R. F., with serum triglyceride level more than 300mg/d
l had reduced H-TGL on a regular diet. However, when his triglyceride concentration returned to normal value on a fat-restricted diet, his H-TGL was also within the normal range. At both of the periods, the pattern of lipoproteins characterized by the presence of an intermediate lipoprotein was not significantly changed. Unknown mechanisms other than the deficiency in H-TGL must be involved in the impaired metabolism of the intermediate lipoprotein.
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