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Germline intragenic SMARCB1 deletions/duplications and larger deletions in chromosome band 22q11.2 encompassing the SMARCB1 gene predispose individuals to the development of rhabdoid tumors and familial schwannomatosis.*
SMARCB1 is a tumor suppressor gene. Consistent with the two-hit hypothesis, individuals with a germline SMARCB1 deletion or duplication (or mutation) are at increased risk for cancer as well as multiple benign schwannomas (schwannomatosis). The second acquired or somatic alteration in these individuals is also a deletion/duplication or mutation that results in loss of function of SMARCB1 on both alleles. Germline alterations of SMARCB1 may be inherited or de novo. For individuals with a personal history of rhabdoid tumor or multiple schwannomas, analysis of tumor tissue as the first test is advised to reduce the risk of a false-negative result. Once the copy number alteration(s) or mutations have been identified, the individual can be screened for those specific mutations in their blood to determine if they are somatic or germline in nature. Depending on the extent of a germline deletion, the individual may be at risk for other phenotypic abnormalities, such as those associated with DiGeorge or Velo-cardio-facial syndrome. If a germline deletion or duplication is found in the patient’s germline, then parental studies are warranted to rule out an inherited SMARCB1/22q11.2 alteration. It is important for genetic counseling purposes to know that cases of germ cell mosaicism of SMARCB1 intragenic deletions, duplications or mutations resulting in multiple affected siblings who developed rhabdoid tumors have been previously reported.*If tumor tissue is unavailable, full sequencing
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