This test analyzes genes associated with familial gastrointestinal stromal tumor syndrome (GIST), which is a rare hereditary gastrointestinal cancer predisposition syndrome.
Genetic testing of these genes may confirm a diagnosis and help guide treatment and management decisions. Identification of a disease-causing variant would also guide testing and diagnosis of at-risk relatives. This test is specifically designed for heritable germline mutations and is not appropriate for the detection of somatic mutations in tumor tissue.
KIT NF1 PDGFRA SDHA SDHB SDHC SDHD
KIT NF1 PDGFRA SDHA SDHB SDHC SDHD
The genes on this panel can also be ordered as part of broader panels to test for different types of hereditary cancer. Depending on the individual’s clinical and family history, one of these broader panels may be appropriate. Any of these broader panels can be ordered at no additional charge.
Gastrointestinal stromal tumors (GISTs) account for less than 1% of all gastrointestinal tumors. Approximately 5,000 new cases are diagnosed in the United States each year. GISTs are typically adult-onset sarcomas that may be either benign or malignant and that can occur anywhere along the GI tract, which includes the esophagus, stomach, gallbladder, liver, small intestine, colon, rectum, anus, and lining of the gut. They arise from a specific type of cell called interstitial cells of Cajal (ICC), which line the walls of the GI tract. More than half of GISTs start in the stomach. The next-largest proportion of cases starts in the small intestine. The third-largest proportion starts in the omentum. The fourth-largest proportion starts in the peritoneum.
Sporadic cases of GIST typically develop only a single tumor while familial cases of GIST can present with multiple tumors, dysphagia, achalasia, and skin findings that include hyperpigmentation and urticaria pigmentosa. GIST is also a feature of neurofibromatosis type 1 and Carney-Stratakis syndrome, an autosomal dominant condition characterized by the development of GIST and/or paragangliomas.
Individuals with a pathogenic variant in one of these genes have an increased risk of malignancy compared to the average person, but not everyone with such a variant will actually develop cancer. Further, GIST can present differently, even among family members. Although there is an increased risk for GIST associated with the genes on this panel, the risk for malignant GIST is currently unclear.
SDHA, SDHB, SDHC, SDHD
These genes collectively account for approximately 5%-7.5% of all GISTs. These tumors have a tendency to appear in children and young adults.
Pathogenic variants in PDGFRA is associated with GIST as well as inflammatory fibroid bowel polyps. GIST appears to be the only tumor with malignant potential associated with this gene, although the data are emerging.
Most cases of familial GIST are due to pathogenic variants in the KIT. Some affected individuals may also present with skin hyperpigmentation, dysphagia, and urticaria pigmentosa, which is a mastocytosis disorder that causes brown or salmon-colored itchy patches to develop on the skin.
Up to 25% of individuals with neurofibromatosis type 1 develop GIST. Many cases are asymptomatic and are found incidentally. Symptomatic GISTs in individuals with NF1 are typically multiple, diagnosed before age 50, and found in the small intestine and stomach.
The genes in the Invitae Familial Gastrointestinal Stromal Tumor Syndrome Panel are associated with familial GIST, but the overall percentage of hereditary GIST cases attributed to these genes is currently unclear. Inclusion of several GIST-related genes is expected to increase the clinical sensitivity of this test.
Familial GIST is inherited in an autosomal dominant pattern.
Testing for familial GIST should be considered in individuals with a personal and/or family history of one or more of the following:
The American College of Medical Genetics has proposed guidelines to determine which individuals are candidates for familial GIST analysis:
Invitae is a College of American Pathologists (CAP)-accredited and Clinical Laboratory Improvement Amendments (CLIA)-certified clinical diagnostic laboratory performing full-gene sequencing and deletion/duplication analysis using next-generation sequencing technology (NGS).
Our sequence analysis covers clinically important regions of each gene, including coding exons, +/- 10 base pairs of adjacent intronic sequence in the transcript listed below. In addition, analysis covers the select non-coding variants specifically defined in the table below. Any variants that fall outside these regions are not analyzed. Any specific limitations in the analysis of these genes are also listed in the table below.
Based on validation study results, this assay achieves >99% analytical sensitivity and specificity for single nucleotide variants, insertions and deletions <15bp in length, and exon-level deletions and duplications. Invitae's methods also detect insertions and deletions larger than 15bp but smaller than a full exon but sensitivity for these may be marginally reduced. Invitae’s deletion/duplication analysis determines copy number at a single exon resolution at virtually all targeted exons. However, in rare situations, single-exon copy number events may not be analyzed due to inherent sequence properties or isolated reduction in data quality. Certain types of variants, such as structural rearrangements (e.g. inversions, gene conversion events, translocations, etc.) or variants embedded in sequence with complex architecture (e.g. short tandem repeats or segmental duplications), may not be detected. Additionally, it may not be possible to fully resolve certain details about variants, such as mosaicism, phasing, or mapping ambiguity. Unless explicitly guaranteed, sequence changes in the promoter, non-coding exons, and other non-coding regions are not covered by this assay. Please consult the test definition on our website for details regarding regions or types of variants that are covered or excluded for this test. This report reflects the analysis of an extracted genomic DNA sample. In very rare cases, (circulating hematolymphoid neoplasm, bone marrow transplant, recent blood transfusion) the analyzed DNA may not represent the patient's constitutional genome.
|Gene||Transcript reference||Sequencing analysis||Deletion/Duplication analysis|
SDHA: Analysis is limited to sequencing analysis. No clinically-relevant del/dups have been reported.