Familial Hypercholesterolemia NGS Panel

Clinical Information

This panel consists of four genes that have been associated with familial hypercholesterolemia. Familial hypercholesterolemia has an estimated prevalence of 1 in 200-250 individuals, and pathogenic variants in LDLR, APOB, PCSK9, or LDLRAP1 account for the majority of cases.  This condition is associated with significant elevations in low-density lipoprotein (LDL) cholesterol. In addition, total cholesterol is typically increased (usually greater than 300 mg/dL in untreated individuals) with normal to slight elevations in triglycerides. Familial hypercholesterolemia is associated with increased risk of premature cardiovascular disease, specifically atherosclerosis, and symptoms include angina, heart attack, and rarely stroke. Other findings include a hazy ring along the outer rim of the iris known as corneal arcus and xanthomas, particularly of the hands and Achilles tendon.

Variants in LDLR, APOB, and PCSK9 are associated with autosomal dominant inheritance; however, biallelic pathogenic variants in LDLR can cause a rare autosomal recessive form of familial hypercholesterolemia. This form of familial hypercholesterolemia increases the prematurity of coronary artery disease. In these cases, childhood onset of signs and symptoms can occur due to dramatically elevated levels of LDL and total cholesterol. Physical findings include planar xanthomas, aortic stenosis, and corneal arcus, which is pathognomonic for familial hypercholesterolemia when it is identified during childhood.

LDLRAP1 is associated with autosomal recessive hypercholesterolemia. Features of this rare disorder include significant elevations of LDL and total cholesterol as well as triglycerides, often with childhood onset. Other physical signs may or may not be present.

Confirmation of pathogenic variants can assist with early detection, surveillance, and treatment, which may include dietary changes, medication, and surgical intervention to reduce the incidence or severity of cardiovascular complications. Identification of pathogenic variants can also lead to cascade testing for other at-risk family members.

 

Technical Information

This panel is performed by Next Generation Sequencing and covers the coding regions of the listed genes and the flanking intronic sequences. Promoter, 3′ untranslated sequences, and deep intronic sequences are also covered, but only known disease-causing variants in these regions will be reported. Variants identified on the panel are confirmed with Sanger sequencing if they do not meet certain quality thresholds.

Pathogenic variants in LDLR are identified in 60-80% of patients with familial hypercholesterolemia. Sequence-level changes are responsible for 90% of pathogenic variants in LDLR, while deletions in this gene account for 2.5-10% of cases. Please note that this analysis is not designed to detect copy number variants. Alterations in APOB are identified in 1-5% of patients, and variants in PCSK9 are responsible for up to 3% of cases. The prevalence of LDLRAP1 variants is considered very rare.

 

Specimen Requirements

• The preferred sample type is 3-4 ml of peripheral blood collected in an EDTA (purple top) tube. Extracted DNA and saliva are also accepted for this test. Blood and saliva kits are available by request.
• Send approximately 5µg of extracted DNA at a requested concentration of 90-130 ng/µl.
• Saliva samples must be submitted in an approved saliva kit.

Transport Instructions

• The blood specimen should be kept at room temperature and delivered via overnight shipping. If shipment is delayed by one or two days, the specimen should be refrigerated and shipped at room temperature. Do not freeze the specimen. Samples collected on Friday can be safely designated for Monday delivery.
• Extracted DNA should be sent at room temperature via overnight delivery.
• Saliva is stable at room temperature and can be delivered via overnight or ground shipping.