The key difference between heterozygous and homozygous familial hypercholesterolemia is that heterozygous familial hypercholesterolemia is a less severe type of familial hypercholesterolemia caused due to one FH allele. In comparison, homozygous familial hypercholesterolemia is a more severe type of familial hypercholesterolemia caused due to two FH alleles.
Familial hypercholesterolemia (FH) is an inherited genetic disorder that affects the body’s ability to manage cholesterol, resulting in very high levels of LDL, or “bad” cholesterol. It is mainly of two types: heterozygous and homozygous familial hypercholesterolemia. If people inherit an FH allele from one parent, they will have heterozygous FH. It means they have one FH allele and one normal allele. If people inherit the FH allele from each of the parents, they will have homozygous FH, meaning they have two FH alleles.
CONTENTS
1. Overview and Key Difference
2. What is Heterozygous Familial Hypercholesterolemia
3. What is Homozygous Familial Hypercholesterolemia
4. Similarities – Heterozygous and Homozygous Familial Hypercholesterolemia
5. Heterozygous vs. Homozygous Familial Hypercholesterolemia in Tabular Form
6. Summary – Heterozygous vs. Homozygous Familial Hypercholesterolemia
What is Heterozygous Familial Hypercholesterolemia?
Heterozygous familial hypercholesterolemia is a type of familial hypercholesterolemia. In this type, people inherit the FH allele from one parent, meaning they have one FH allele and one normal allele. It is a less severe type of familial hypercholesterolemia. About 1 in 250 people worldwide have this type of familial hypercholesterolemia. Heterozygous FH is characterized by very high LDL cholesterol, above 190 for adults or above 160 for children. It also has a family history of heart disease or stroke. The signs and symptoms of this condition may include elevated cholesterol from birth (350-550 mg/dL), coronary events such as myocardial infarction (MI) or sudden cardiac death, xanthomas (fatty deposits under the skin on the Achilles tendon or the joints of the hand), xanthelasma (fatty deposits under the skin on the eyelids) or corneal arcus (a grayish ring on the periphery of the cornea).
Figure 01: Corneal Arcus
Heterozygous familial hypercholesterolemia can be diagnosed through family history, physical examination, blood tests such as cholesterol screening, and genetic tests. Furthermore, the treatment options for this condition include lifestyle changes and medications like statins, bile acid sequestrants, ezetimibe, fibrates, nicotinic acid, and PCSK9 inhibitors.
What is Homozygous Familial Hypercholesterolemia?
Homozygous familial hypercholesterolemia is a severe form of familial hypercholesterolemia that occurs when an individual inherits the FH allele from both parents, resulting in two FH alleles. Approximately 1 in one million people worldwide have homozygous familial hypercholesterolemia. The signs and symptoms include cholesterol levels into the 700 or even 1,000 mg/dL, bumps or lumps around knees, knuckles, or elbows, swollen or painful Achilles tendon, yellowish areas around the eyes, and a whitish-gray color in the shape of a half-moon outside of the cornea and heart problems.
Homozygous familial hypercholesterolemia can be diagnosed through cholesterol tests and genetic testing. Furthermore, homozygous familial hypercholesterolemia can be treated through medications such as statins, ezetimibe (Zetia), and PCSK9 inhibitors, undergoing a procedure that filters the excess cholesterol from the blood, and liver transplants.
What are the Similarities Between Heterozygous and Homozygous Familial Hypercholesterolemia?
- Heterozygous and homozygous familial hypercholesterolemia are two types of familial hypercholesterolemia characterized by elevated cholesterol levels.
- Both types can be diagnosed through blood tests and genetic testing.
- They are mainly treated through specific medications.
What is the Difference Between Heterozygous and Homozygous Familial Hypercholesterolemia?
Heterozygous familial hypercholesterolemia is a less severe type of familial hypercholesterolemia caused due to one FH allele. In contrast, homozygous familial hypercholesterolemia is a more severe type of familial hypercholesterolemia caused due to two FH alleles. Thus, this is the key difference between heterozygous and homozygous familial hypercholesterolemia. Furthermore, about 1 in 250 people worldwide have heterozygous familial hypercholesterolemia, while approximately 1 in one million people worldwide have homozygous familial hypercholesterolemia.
The infographic below presents the differences between heterozygous and homozygous familial hypercholesterolemia in tabular form for side-by-side comparison.
Summary – Heterozygous vs. Homozygous Familial Hypercholesterolemia
Familial hypercholesterolemia (FH) is a genetic disorder that increases the likelihood of having coronary heart disease at a younger age. It is mainly of two types: heterozygous and homozygous familial hypercholesterolemia. In heterozygous familial hypercholesterolemia, people inherit one FH allele from one parent. Therefore, they have one FH allele and one normal allele. On the other hand, in homozygous familial hypercholesterolemia, people inherit two FH alleles from each of the parents, so they have two FH alleles. Moreover, heterozygous familial hypercholesterolemia is less severe, while homozygous familial hypercholesterolemia is more severe. So, this summarizes the difference between heterozygous and homozygous familial hypercholesterolemia.
Reference:
1. Brumit, Marie Louise. “What Is Heterozygous Familial Hypercholesterolemia?” Family Heart Foundation.
2. Cuchel, Marina, et al. “Homozygous Familial Hypercholesterolaemia: New Insights and Guidance for Clinicians to Improve Detection and Clinical Management. A Position Paper from the Consensus Panel on Familial Hypercholesterolaemia of the European Atherosclerosis Society.” European Heart Journal.
Image Courtesy:
1. “Four representative slides of corneal arcus (cropped)” By Loren A Zech Jr and Jeffery M Hoeg – Correlating corneal arcus with atherosclerosis in familial hypercholesterolemia (CC BY 2.0) via Commons Wikimedia