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Two cases with transient lipoprotein lipase (LPL) activity impairment: evidence for the possible involvement of an
H Nagasaka1,2, H Kikuta3, H Chiba4
1Department of Pediatrics, Hokkaido University School of Medicine, Kita-ku N. 15 W.7, 060-8638, Sapporo, Japan. nagasa-hirono@k2.dion.ne.jp.
Insights
Severe hypertriglyceridemia in infants was linked to temporarily reduced lipoprotein lipase (LPL) activity. Researchers propose transient inhibitors may cause this LPL impairment in infants.
Area of Science:
- Biochemistry
- Pediatrics
- Lipid Metabolism
Background:
- Infantile hypertriglyceridemia, specifically Fredrickson type V hyperlipidemia, presents a diagnostic challenge.
- Lipoprotein lipase (LPL) activity is crucial for triglyceride clearance, and its impairment can lead to severe hypertriglyceridemia.
Observation:
- Two premature, low-birth-weight infants developed severe hypertriglyceridemia with impaired post-heparin plasma LPL activity despite normal LPL mass.
- Mothers also showed slightly to moderately impaired LPL activity; no genetic mutations in LPL or apo C-II were found.
- Dietary intervention normalized triglyceride and cholesterol levels, but impaired LPL activity and low HDL cholesterol persisted until age 2.
Findings:
- Transiently impaired LPL activity, not a defect in the LPL enzyme itself, was the cause of severe hypertriglyceridemia in these infants.
- The study suggests the potential transient occurrence of inhibitors affecting LPL activity.
- Low HDL cholesterol levels persisted despite normalized triglyceride levels and normal LCAT and CETP activity.
Implications:
- This study highlights a novel cause of severe hypertriglyceridemia in infants, emphasizing the role of transient LPL inhibition.
- Understanding the mechanisms behind transient LPL impairment is crucial for managing pediatric lipid disorders.
- Further research is needed to identify the specific inhibitors and understand the persistence of low HDL cholesterol.
Unlabelled:
Two independent severe hypertriglyceridemic infants with transiently impaired lipoprotein lipase (LPL) activity were observed and the causes were explored. Both infants were female, born prematurely with low birth weight and developed hypertriglyceridemia (Fredrickson type V hyperlipidemia: high VLDL and low LDL/HDL) a few months after birth. While mass levels of their post-heparin plasma LPL and apoprotein C-II (apo C-II), a physiological activator of LPL, were normal, their post-heparin plasma LPL activities were remarkably impaired. Both of their mothers' post-heparin plasma LPL activities were slightly or moderately impaired as well, without a decrease in the LPL mass level. No mutations in the genes for LPL and apo C-II were detected in either patient. In an in vitro study with their serum at onset, we could not detect any distinct circulating inhibitors for LPL. There was no data supporting infection or autoimmune diseases, which might have an impact on LPL activity, during the follow-up period. Levels of their plasma triglyceride (TG) and total cholesterol (TC) were decreased quickly by a dietary intervention with medium-chain triglyceride (MCT) milk and kept normal even after stopping the intervention at around age 1 year. However, their low post-heparin LPL activity persisted and returned to normal at around age 2 years. Their low HDL cholesterol levels persisted even after recovery of the TG and TC levels, although lecithin:cholesterol acyltransferase (LCAT) and cholesterol-ester-transfer protein (CETP), two key enzymes of HDL metabolism, were normal throughout the course. The exact reasons why their post-heparin LPL activities were impaired for a certain period and why their HDL cholesterol levels have remained low are still unclear.
Conclusion:
Transiently impaired LPL activity with no defect in LPL enzyme induced severe hypertriglyceridemia in infants. The transient occurrence of inhibitor(s) for LPL was proposed.
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