DISEASE INFORMATION
Familial hypocalciuric hypercalcemia (FHH) is an autosomal dominant condition caused by mutations in the calcium sensing receptor gene (CASR). FHH is characterized by hypercalcemia, hypocalciuria, hypermagnesemia, and normal to high levels of parathyroid hormone (PTH). The prevalence is estimated as high as 1 in 16,000 and most cases is asymptomatic however some may present with lifelong hypercalcemia. Those with FHH are at increased risk for developing chondrocalcinosis, pancreatitis, gallstones or kidney stones.^{1, 2, 3, 4}

Patients with FHH are often misdiagnosed with a more common and more severe condition called primary hyperparathyroidism (PHPT). PHPT is also characterized by hypercalcemia; treatment for this condition requires parathyroidectomy, a procedure not necessary for those with FHH.³ A feature that distinguishes PHPT from FHH is elevated circulating PTH levels, however approximately 5 to 15% of individuals with PHPT show circulating PTH in the upper normal limit.⁵

FHH is caused by loss-of-function mutations in the CASR gene. Gain-of-function mutations in this gene are responsible for autosomal dominant hypocalcemia (ADH) which is characterized by hypocalcemia, hypercalciuria, and sporadic hypothyroidism.⁸ Homozygous or compound heterozygous loss-of-function mutations in CASR result in neonatal severe hyperparathyroidism (NSHPT) a severe and possibly lethal condition. Symptoms appear in infancy and include extreme hypercalcemia, failure to thrive, hypotonia, skeletal demineralization, and severe parathyroid hyperplasia.^{6, 7} Some de novo mutations may cause a mild or transient version of NSHPT. Treatment may require parathyroidectomy.¹

TESTING BENEFITS & INDICATIONS
Diagnostic testing is recommended for individuals known or suspected to have familial hypocalciuric hypercalcemia (FHH). Diagnostic testing is also indicated in individuals suspected of having primary hyperparathyroidism (PHPT). Distinguishing  between FHH and PHPT can help prevent unnecessary parathyroidectomy in those with FHH. Carrier screening is available for relatives of FHH patients with a known mutation. Diagnostic testing is also available for pregnancies at risk for neonatal severe hyperparathyroidism (NSHPT).  

TEST DESCRIPTION
This Ambry Test is a gene sequence analysis performed by PCR-based double-stranded automated sequencing in the sense and antisense directions for exons 2-7 of the CASR gene, plus at least 20 bases into the 5’ and 3’ ends of all the introns. Specific mutation analysis for individual CASR mutations known to be in the family is also available.

MUTATION DETECTION RATE
Mutations are present in about 90% of FHH families (clinical sensitivity), and approximately 99% of CASR mutations are detectable by this test (analytical sensitivity).

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 Marx SJ et al. Medicine.1981;60:397-412.
² Law WM & Heath H. Ann Intern Med.1985;102:511-519.
³ Paterson CR & Gunn A. Lancet.1981;2:61-63.
⁴ Heath H III. Endocrinol Metab Clin North Am.1989;18:723-740.
⁵ Gunn & Wallace. Ann Clin Biochem.1992;29:52-586.
⁶ Spiegel AM et al. J Pediatr.1977;90:269-272.
⁷ Cole DEC et al. J Craniofac Genet Dev Biol.1990;10:205-214.
⁸ Pollak MR et al. Nat Genet.1994;8:303-307.

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 Hypocalciuric Hypercalcemia (FHH) analyzes the following types of mutations: nucleotide substitutions, small deletions, small insertions and small indels. It is not intended to analyze the following types of mutations: gross deletions/duplications, 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 a mutation in the undetectable group. The Ambry Test: FHH is designed and validated to be capable of detecting >99% of described mutations in CASR (considering less than 1% to be the other types of mutations). FHH is a complex clinical disorder, which in most cases is due to alterations in CASR generally detected by the Ambry Test: FHH except as noted above. Mutations in other genes or the regions not tested by the Ambry Test: FHH can also give rise to clinical conditions similar to FHH. 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.