Question

Familial hypercholesterolemia (FH) is an inherited trait in humans that results in higher than normal serum cholesterol levels (measured in milligrams of cholesterol per deciliter of blood (mg/dl)). People with serum cholesterol levels that are roughly twice normal have a 25 times higher frequency of heart attacks than unaffected individuals. People with serum cholesterol levels three or more times higher than normal have severely blocked arteries and almost always die before they reach the age of 20. The pedigrees above show the occurrence of FH in four Japanese families: a. What is the most likely mode of inheritance of FH based on this data? Are there any individuals in any of these pedigrees who do not fit your hypothesis? What special conditions might account for such individuals? b. Why do individuals in the same phenotypic class (unfilled, yellow, or orange symbols) show such variation in their levels of serum cholesterol?

Answer 1

Answer:

Thanks for you question. Your hypothesis suggests a linear relationship between serum Cholesterol levels and MI. This hypothesis seems to ignore the difference in the prevalence and effectiveness of LDL receptors in the FH patient.

FH patients who have inherited the mutation from both parents have very few LDL receptors in their blood and therefore almost no ability to pass the unused Cholesterol through the liver. FH patients who are heterozygous will have more LDL receptors although both will find Cholesterol removal problematic without the addition of a PCSK9 inhibitor.

In short, your hypothesis need to account for other factors that are in play.

Explanation:

Consider my case. I am a 64 year old male who has Heterozygous Familial Hypercholesterolemia. Before treatment at age 12 my Total cholesterol was 510 mg/dl. My genetic testing shows two mutations to the LDL Receptor gene with only one mutation being pathogenic. My first heart attack was at 47 and first stroke at 62. My current LDL is too low to detect with the use of a PCSK9 inhibitor (Repatha®).