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Test Code LDLRS Familial Hypercholesterolemia, LDLR Full Gene Sequencing

Performing Laboratory

Mayo Medical Laboratories in Rochester

Reporting Name

LDLR, Full Gene Sequence

Specimen Type

Whole Blood EDTA


Specimen Required


Multiple cardiovascular-related gene sequencing tests can be performed on a single specimen after a single extraction. See Multiple Cardiovascular-Related Gene Sequencing Tests in Special Instructions for a list of tests that can be ordered together.

 

Container/Tube: Lavender top (EDTA)

Specimen Volume: 3 mL

Collection Instructions: Send specimen in original tube.

Additional Information: Include physician name and phone number with the specimen.


Reject Due To

Hemolysis

NA

Lipemia

NA

Icterus

NA

Other

NA

Specimen Stability Information

Specimen Type Temperature Time
Whole Blood EDTA Ambient (preferred)
  Refrigerated 

Specimen Minimum Volume

0.5 mL

Day(s) and Time(s) Performed

Varies

Specimen Retention Time

2 months (extracted DNA only is saved)

Analytic Time

10 days

Reference Values

An interpretive report will be provided.

Useful For

Aiding in the diagnosis of familial hypercholesterolemia (FH)

 

Distinguishing the diagnosis of FH from other causes of hyperlipidemia, such as familial defective apoB-100 and familial combined hyperlipidemia

Method Name

Polymerase Chain Reaction (PCR) Followed by DNA Sequence Analysis

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

81406-LDLR (low density lipoprotein receptor) (eg, familial hypercholesterolemia), full gene sequence

LOINC Code Information

Result ID Test Result Name Result LOINC Value
30381 Interpretation 69047-9
LDLMS Sequencing 56159-7
15598 Comment 48767-8
30382 Reviewed By 18771-6
31628 Result 56159-7

Clinical Information

Familial hypercholesterolemia (FH) is an autosomal dominant disorder that is characterized by high levels of low-density lipoprotein (LDL) cholesterol and associated with premature cardiovascular disease and myocardial infarction. FH is caused by variants in the LDLR gene, which encodes for the LDL receptor. LDLR variants impair the ability of the LDL receptor to remove LDL cholesterol from plasma via receptor-mediated endocytosis, leading to elevated levels of plasma LDL cholesterol and subsequent deposition in the skin and tendons (xanthomas) and arteries (atheromas).

 

FH can occur in either the heterozygous or homozygous state, with 1 or 2 variant LDLR alleles, respectively. In general, FH heterozygotes have 2-fold elevations in plasma cholesterol and develop coronary atherosclerosis after the age of 30. Homozygous FH individuals have severe hypercholesterolemia (>650 mg/dL) with the presence of cutaneous xanthomas prior to 4 years of age, childhood coronary heart disease, and death from myocardial infarction prior to 20 years of age. Heterozygous FH is prevalent among many different populations, with an approximate average worldwide incidence of 1 in 500 individuals, but as high as 1 in 67 to 1 in 100 individuals in some South African populations and 1 in 270 in the French Canadian population. Homozygous FH occurs at a frequency of approximately 1 in 1,000,000.

 

Treatment is aimed at lowering plasma LDL levels and increasing LDL receptor activity. Identification of LDLR variant(s) in individuals suspected of having FH helps to determine appropriate treatment. FH heterozygotes are often treated with 3-hydroxy-3-methylglutaryl CoA reductase inhibitors (ie, statins), either in monotherapy or in combination with other drugs such as nicotinic acid and inhibitors of intestinal cholesterol absorption. Such drugs are generally not effective in FH homozygotes; treatment in these individuals may consist of LDL apheresis, portacaval anastomosis, and liver transplantation.

 

The LDLR gene maps to chromosome 19p13 and consists of 18 exons spanning 45 kb. Hundreds of variants have been identified in the LDLR gene, the majority of them occurring in the ligand binding and epidermal growth factor (EGF) precursor homology regions in the 5' region of the gene (type II and III variants, respectively). The majority of LDLR mutations are missense, small insertion, deletion and other point variants, most of which are detected by full-gene sequencing. Approximately 10% to 15% of LDLR variants are large rearrangements, such as exonic deletions and duplications, which cannot be detected by full-gene sequencing.

Interpretation

An interpretive report will be provided.

Cautions

Blood samples may contain donor DNA if obtained from patients who received heterologous blood transfusions or allogeneic blood or marrow transplantation. Results from samples obtained under these circumstances may not accurately reflect the recipient's genotype. For individuals who have received blood transfusions, the genotype usually reverts to that of the recipient within 6 weeks. For individuals who have received allogeneic blood or marrow transplantation, a pretransplant DNA specimen is recommended for testing.

 

Absence of a variant does not preclude the diagnosis of familial hypercholesterolemia (FH) unless a specific variant has been previously identified in an affected family member.

 

This method will not detect large rearrangement-type variants or variants that occur in the introns (except in the splicing regions) and regulatory regions (except the sterol-regulated portion of the promoter) of the gene.

 

Sometimes a genetic alteration of unknown significance may be identified. In this case, testing of family members may be useful to determine pathogenicity of the alteration.

Clinical Reference

1. Hobbs H, Brown MS, Goldstein JL: Molecular genetics of the LDL receptor gene in familial hypercholesterolemia. Hum Mutat 1992;1:445-446

2. Goldstein JL, Hobbs H, Brown MS: Familial hypercholesterolemia. In The Metabolic Basis of Inherited Disease. Edited by CR Scriver, AL Beaudet, D Valle, WS Sly. New York, McGraw-Hill Book Company, 2006, pp 2863-2913

3. van Aalst-Cohen ES, Jansen AC, Tanck MW, et al: Diagnosing familial hypercholesterolaemia: the relevance of genetic testing. Eur Heart J 2006;27:2440-2446

Method Description

All 18 exons, splice junctions, and a portion of the promoter and 3' untranslated region (UTR) of the LDLR gene are amplified by PCR and then subjected to direct bidirectional DNA sequence analysis.(Unpublished Mayo method)

Profile Information

Test ID Reporting Name Available Separately Always Performed
LDLRQ LDLR, Full Gene Sequence No Yes
LDLFQ LDLR Gene Sequencing No Yes

Disease States

  • Hyperlipidemia

Forms

1. Familial/Autosomal Dominant Hypercholesterolemia Patient Information (T637) is required in Special Instructions

2. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (T576) is available in Special Instructions.

3. If not ordering electronically, complete, print, and send a Cardiovascular Test Request Form (T724) with the specimen (http://www.mayomedicallaboratories.com/it-mmfiles/cardiovascular-request-form.pdf).