PGLFirstTM (FORMERLY PARAGANGLIOMA-PHEOCHROMOCYTOMA (PGL-PCC) SYNDROME PANEL) is a next generation sequencing panel that simultaneously analyzes 7 genes associated with an increased risk of developing paragangliomas and/or pheochromocytomas.
Ambry utilizes next generation sequencing (NGS) to offer PGLFirst, a comprehensive non-syndromic hereditary PGL/PCC panel. Genes on this panel include MAX, SDHA, SDHAF2, SDHB, SDHC, SDHD, TMEM127. Full gene sequencing and gross deletion/duplication analysis is performed for all 7 genes. PGLNext is a comprehensive syndromic and non-syndromic hereditary PGL/PCC panel of 12 genes. Specific Site Analysis is available for individual gene mutations identified in a family.
Paragangliomas (PGLs) are often benign, neuroendocrine tumors of the autonomic nervous system originating from the external ganglia. Pheochromocytomas (PCCs) are paragangliomas that are confined to the adrenal medulla. PGLs are further subdivided into sympathetic and parasympathetic tumors, depending upon their site of origin. Sympathetic PGLs commonly hypersecrete catecholamines and are typically located in the chest, abdomen and pelvis. Parasympathetic PGLs are primarily non-secretory and occur along the nerves in the head, the neck, and the upper mediastinum (termed head and neck PGLs or HNPGLs).1,2
The prevalence of PGLs in the U.S. is 1 in 2,500 to 1 in 6,500, although this is likely an underestimate. The average age of diagnosis is between 40-50 years.2,3 Approximately 75% of PGL/PCCs are benign; however, morbidity and mortality are associated with high levels of circulating catecholamines, which can lead to hypertension and stroke.1,3 Published population studies have found that at least 10-30% individuals with PGL/PCCs have an inherited germline mutation in one of the known susceptibility genes.1,4-6
MAX is a tumor suppressor gene associated with PCC susceptibility. In one study of twelve MAX mutation carriers with PCC, 25% of patients showed metastasis, suggesting that, similar to SDHB, MAX mutations are associated with an increased metastatic potential.7 The exact PCC lifetime risk is not yet established for MAX mutation carriers. Seemingly sporadic PCCs may be due to paternal transmission of the mutant allele.1,3,7
SDHA, SDHAF2, SDHB, SDHC, SDHD are all genes associated with hereditary PGL/PCC syndrome. Germline mutations in these genes have been associated with susceptibility to head and neck paragangliomas (HNPGLs), extra-adrenal PGLs/PCCs and, rarely, renal cell carcinoma (RCC) with gastrointestinal stromal tumors (Carney-Stratakis syndrome).8 SDHB-associated RCC can be of varied histology with reported cases of clear cell, papillary, granular, and mixed.9,10 The exact lifetime risk for PCC is not yet established for SDHB mutation carriers.11 The SDHD and SDHAF2 genes are subject to the effects of imprinting (parent-of-origin effects), and cancer risk is correlated with paternal transmission.12-14 Mutations in the SDHB and SDHD genes have also been associated with PTEN mutation-negative Cowden syndrome.15
TMEM127 is a proposed tumor suppressor gene associated with PGL/PCC susceptibility.16 TMEM127 mutations demonstrate an autosomal dominant pattern of inheritance with unknown penetrance.1,3 TMEM127-associated PCCs can present bilaterally or unilaterally, and may also be found in patients with no family history of PCC.11,16 One study reported TMEM127 mutations in 2 of 48 patients with PGL.16
Germline mutations in SDHD cause the highest susceptibility to head and neck paragangliomas, however, mutations in SDHB, SDHC, and SDHAF2 have also been reported in these patients. Germline mutations in SDHB and MAX have the highest risk of malignancy. Mutations in SDHAF2, SDHD, RET, and MAX cause the highest susceptibility to multiple or bilateral PGL/PCCs. To note, MEN1, NF1, RET, and VHL mutations have also been found to be part of the hereditary PGL/PCC spectrum. 17
Genetic testing algorithms exist, however, recent data and guidelines suggest that all individuals with a PGL or PCC should be offered diagnostic testing for hereditary PGL/PCC susceptibility.4 Increased surveillance and treatment is available for those found to carry a mutation.17
Common Red Flags for Hereditary Cancer
Benefits of Testing:
Identifying patients with an inherited susceptibility for PGL/PCC can help with medical management and risk assessment. For example, this information can:
PGLFirst analyzes 7 genes (listed above). All genes are evaluated by next generation sequencing (NGS) or Sanger sequencing of all coding domains, and well into the flanking 5’ and 3’ ends of all the introns and untranslated regions. Clinically significant intronic findings beyond 5 base pairs are always reported. Intronic variants of unknown or unlikely clinical significance are not reported beyond 5 base pairs from the splice junction. Additional Sanger sequencing is performed for any regions missing or with insufficient read depth coverage for reliable heterozygous variant detection. Reportable small insertions and deletions, potentially homozygous variants, variants in regions complicated by pseudogene interference, and single nucleotide variant calls not satisfying 100x depth of coverage and 40% het ratio thresholds are verified by Sanger sequencing.18 Gross deletion/duplication analysis is performed for the covered exons and untranslated regions of all 7 genes using read-depth from NGS data with confirmatory multiplex ligation-dependent probe amplification (MLPA) and/or targeted chromosomal microarray.
PGLFirst can detect >99.9% of described mutations in the included genes listed above, when present (analytic sensitivity).
|TEST CODE||TECHNIQUE||CALENDAR DAYS|
|5450||PGLFirst reflex to PGLNext||14-42|
|5416||Single Site Analysis||7-14|