DISEASE INFORMATION
Familial hypercholesterolemia (FH) is typically an autosomal dominant disease characterized by the presence of high levels of plasma LDL (low density lipoproteins) cholesterol in the body, increasing the risk for premature coronary heart disease (CHD) and myocardial infarction.¹ The majority of autosomal dominant FH cases are associated with loss-of- function mutations in the gene for the low-density lipoprotein receptor (LDLR).² Affected individuals present high levels of plasma LDL cholesterol, which increases the risk of premature coronary artery disease, myocardial infarction, and atherosclerotic plaque formation. Defective LDL-receptors cause deposition of cholesterol in different parts of the body causing diseases such as xanthelasma (skin), xanthomas (tendons), and coronary arteries (atherosclerosis).^{3, 4}

There are approximately 1 in 500 individuals with heterozygous LDLR mutations and 1 in a million individuals with homozygous mutations in the general population.^{1, 2} Heterozygotes present a 2- to 3- fold elevation in plasma LDL-cholesterol and develop symptoms such as tendinous xanthomas, corneal arcus, and premature coronary artery disease.^2,4 Homozygotes also present planar xanthomas, with plasma LDL-cholesterol increases 6- to 8-fold, and death from myocardial infarctions during the first two decades of life is common.⁵ As a result of founder effect, FH is much more common in some population groups such as French Canadians, Afrikaners, Lebanese, Finns, and Ashkenazi Jews.⁶

In addition to mutations in the LDLR gene, mutations in the APOB gene contribute to another type of familial hypercholesterolemia known as familial defective apolipoprotein B-100 (FDB).^{3, 7} Apolipoprotein B-100 (APOB) is the major component of low density lipoproteins (LDL) and plays a crucial role in the binding of LDL with LDL receptors.⁷ These APOB mutations fall within the receptor binding domain of the gene and decrease the binding efficiency of lipoproteins with LDL receptors, leading to the accumulation of plasma LDL in FDB.

TESTING BENEFITS & INDICATIONS
Early diagnostic testing for individuals known or suspected to have Familial Hypercholesterolemia will help decrease the risks associated with FH. Carrier screening for relatives of FH patients, at risk pregnancies, and carrier testing for known familial mutations will also decrease the risk of known hypercholesterolemia effects.

TEST DESCRIPTION
LDLR 5’UTR and exons 1-18 plus at least 20 bases into the 5’ and 3’ ends of all the introns are analyzed. For APOB sequence analysis, a 708 base pair fragment of APOB exon 26 containing the most frequently occurring mutations associated with FH is analyzed. The following sites are used to search for previously described LDLR and APOB mutations and polymorphisms: http://www.ucl.ac.uk/ldlr/ LOVDv.1.1.0 (LDLR only), Human Gene Mutation Database (HGMD), and online search engines (e.g., PubMed).

MUTATION DETECTION RATE
The Ambry Test: Familial Hypercholesterolemia AMPLIFIED (LDLR and APOB) is designed and validated to be capable of detecting > 99% of described mutations in LDLR (considering less than 1% to be the other types of mutations) and > 80% of described mutations in APOB relevant for FH.

SPECIMEN REQUIREMENTS
Blood: Collect 3-5 cc from adult or 2 cc minimum from child into EDTA purple-top tube (first choice) or ACD yellow-top tube (second choice). Store at room temperature or refrigerate. Ship at room temperature.
Blood Spot: Call for availability.
Saliva: Collect 2 ml into Oragene™ DNA Self-Collection container. Store and ship at room temperature.
DNA: Send 20 µg in TE at 50-100 ng/µl. Store frozen and ship on ice or dry ice.
Prenatal: Prenatal testing is available. Please call an Ambry Genetic Counselor to discuss your case.

REFERENCES
¹ Hopkins PN. International Journal of Cardiology 2003;89: 13-23.
² Hobbs H et al. Annu. Rev. Genet. 1990;24:133-70.
³ Schmidt HH et al. J Clin Endocrinol Metab. 1998 Jun;83(6):2167-74.
⁴ Varret M et al. Clin Genet 2008: 73: 1–13.
⁵ Bertolini S et al. Arterioscler. Thromb. Vasc. Biol. 1999;19;408-418.
⁶ Austin M et al. Am J Epidemiol 2004;160:407–420.
⁷ Liyanage KE et al. Ann Clin Biochem 2008; 45: 170–176.
⁸ Rader DJ et al. J. Clin. Invest. 2003; 111: 1795–1803.

DISCLAIMER
This test was developed and its performance characteristics were determined by Ambry Genetics Corporation.  The laboratory is regulated under the Clinical Laboratory Improvement Amendments 2003 as qualified to perform nonwaived testing.  The Ambry Test:  Familial Hypercholesterolemia AMPLIFIED (LDLR and APOB) analyzes the following types of mutations: nucleotide substitutions, small deletions, small insertions (including small repeat expansion), small indels, and gross deletions/duplications. It is not intended to analyze the following types of mutations: gross rearrangements, deep intronic variations, and other unknown abnormalities. The pattern of mutation types varies with the gene tested and the Ambry Test detects a high but variable percentage of known and unknown mutants of the classes stated. A negative result from the analysis cannot rule out the possibility that the tested individual carries a rare unexamined mutation or mutation in the undetectable group. The Ambry Test:  Familial Hypercholesterolemia AMPLIFIED (LDLR and APOB) is designed and validated to be capable of detecting > 99% of described mutations in LDLR (considering less than 1% to be the other types of mutations) and > 80% of described mutations in APOB relevant for FH. Familial Hypercholesterolemia is a complex clinical disorder, which in most cases is due to alterations in LDLR generally detected by The Ambry Test: Familial Hypercholesterolemia AMPLIFIED (LDLR and APOB) except as noted above. Mutations in other genes or the regions not tested by The Ambry Test: Familial Hypercholesterolemia AMPLIFIED (LDLR and APOB) can also give rise to clinical conditions similar to Familial Hypercholesterolemia. Although molecular tests are highly accurate, rare diagnostic errors may occur. Possible diagnostic errors include sample mix-up, erroneous paternity identification, technical errors, clerical errors, and genotyping errors. Genotyping errors can result from trace contamination of PCR reactions, from maternal cell contamination in fetal samples, from rare genetic variants, which interfere with analysis, or from other sources. This report does not represent medical advice. Any questions, suggestions, or concerns regarding interpretation of results should be forwarded to a genetic counselor, medical geneticist, or physician skilled in interpretation of the relevant medical literature.