Familial Hyperchylomicronemia
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Familial Hyperchylomicronemia

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Summary

Familial hyperchylomicronemia, also known as type I hyperlipoproteinemia, is an autosomal recessive disorder characterized by high levels of chylomicrons. It is caused by homozygous mutations in lipoprotein lipase or its cofactor Apo C-II, which together normally cleave and release the chylomicrons’ triglyceride contents. Since chylomicrons carry triglycerides, hypertriglyceridemia is therefore a hallmark of the disease. High triglyceride levels are also a common cause of pancreatitis, which therefore may also be seen. Other findings include xanthomas, hepatosplenomegaly, and a creamy supernatant layer in blood samples.

Key Points

  • Familial hyperchylomicronemia
    • Also known as type I hyperlipoproteinemia
    • Genetics
      • Autosomal recessive
        • This disease is really rare, which is at least in part due to this
      • Caused by homozygous defects in either:
        • Lipoprotein lipase
        • Apo C-II
      • I like to think of this disease as an extreme form of familial hypertriglyceridemia, which can be caused by heterozygous mutations in lipoprotein lipase / Apo C-II
    • Labs
      • Elevated chylomicronselevated triglycerides
      • High cholesterol
        • Chylomicrons primarily contain triglycerides, but they also carry dietary cholesterol and fat-soluble vitamins
        • Knowing this won't really get you any questions right, though, and this isn't the main point of the disease
    • Clinical Features
      • Pancreatitis
        • Caused by increased triglycerides
      • Hepatosplenomegaly
        • Familial hyperchylomicronemia is characterized by so much fat / triglycerides that there is even a creamy fat layer in the blood. It should come as no surprise that there’s also fatty infiltration of the organs.
      • Xanthomas (eruptive / pruritic)
      • Creamy layer in supernatant
        • There’s so much fat / triglycerides in the blood
      • No increased risk of atherosclerosis
        • Chylomicrons are primarily associated with triglycerides and not cholesterol. The other hyperlipoproteinemias that increase primarily cholesterol-rich lipoproteins are those that are most atherogenic.