Familial hyperinsulinism (FHI) occurs at increased frequency in individuals of Ashkenazi Jewish descent, with a carrier frequency of 1 in 52. FHI is characterized by hypoglycemia due to unregulated release of insulin from cells in the pancreas. This disease varies in severity and age at presentation. If untreated, symptoms may lead to irreversible brain damage and can be fatal.
FHI mutation analysis tests for two mutations for a 97% carrier detection rate in the Ashkenazi Jewish population
Mutation(s) include:c.3989-9G>A; c.4160_4162delTCT (p.F1387del) (legacy name: F1388del)
Polymerase chain reaction (PCR); primer extension; flow-sorted bead array analysis
10-14 days (when cell culture is required, add ~2 weeks)
Whole blood or mouthwash (see specimen kit for detailed instructions), amniotic fluid, chorionic villi, cultured amniotic fluid, cultured chorionic villi.
Postnatal: 10 mL whole blood or mouthwash / Prenatal: 10 mL amniotic fluid in orange-top polypropylene tube, 10-15 mg chorionic villi in laboratory provided screw-top tubes with sterile transport medium or one T-25 flask of confluent cells.
Lavender-top (EDTA) tube or yellow-top (ACD-A) tube or mouthwash kit
Mouthwash collection: Patient should not eat, drink, smoke or chew gum for at least one hour prior to collection. (See specimen kit for detailed instructions).
Mouthwash samples can be sent when ordering up to two tests. When ordering more than two tests, blood samples are required. 10 mL of Scope® mouthwash that has been swished vigorously for at least 1 minute. Collect in orange-top 50 mL polypropylene tube.
Prenatal testing: Integrated Genetics clients should call 800-848-4436 to speak to a laboratory genetic coordinator before collecting any specimens. In some circumstances, specimens from other family members may be required.
All prenatal specimens (including cord blood) must be accompanied by a maternal blood or mouthwash specimen for analysis of possible maternal cell contamination.
Discard first 2 mL; then 10 mL amniotic fluid in 15 mL orange-top polypropylene tube, 10-15 mg chorionic villi in laboratory-provided screw-top tubes with sterile transport medium or one T-25 flask of confluent cells.
Additional sample must be obtained for back-up culture at one of our cytogenetics laboratories or another facility. If additional testing is desired, more amniotic fluid is needed. For example, chromosome analysis requires an additional 15-25 mL (see Cytogenetics – Amniotic Fluid Chromosome Analysis test page) and AFAFP requires an additional 2 mL (see Amniotic Fluid Alpha-Fetoprotein - AFAFP test page).
Causes for Rejection
Frozen specimen; hemolysis; quantity not sufficient for analysis; improper container; unlabeled or mislabeled specimen
Maintain specimen at room temperature.
Couples who are planning a pregnancy or who are already pregnant may decide to have testing to find out if they are carriers and at risk of having a baby with FHI. It is standard of care to offer carrier screening to individuals of Ashkenazi Jewish descent for Bloom syndrome, Canavan disease, cystic fibrosis, familial dysautonomia, Fanconi anemia group C, Gaucher disease, mucolipidosis type IV, Niemann-Pick disease type A, spinal muscular atrophy and Tay-Sachs disease. If both parents are found to be carriers, prenatal diagnosis by CVS or amniocentesis is available.
False positive or false negative results may occur for reasons that include: genetic variants, technical handling, blood transfusions, bone marrow transplantation, mislabeling of samples, or erroneous representation of family relationships.