Question
A 20-year-old man is examined by a new family physician who discovers numerous pigmented patches and pedunculated skin tumors on his chest. Biopsy of a tumor discloses a benign neoplasm derived from Schwann cells. Neither the patient’s father nor mother shows signs of this disease. This patient most likely carries a mutation in a gene that encodes which of the following proteins?
| A. |
Epidermal growth factor receptor
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| B. |
GTPase activating protein
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| C. |
NF-κB transcription factor
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| D. |
Ras protein p21
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Show Answer
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Correct Answer � B
Explanation
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Answer: B GTPase activating protein
Neurofibromatosis type 1 (NF1) is characterized by disfiguring neurofibromas, areas of dark pigmentation of the skin (café au lait spots), and pigmented lesions of the iris (Lisch nodules).
It is one of the more common autosomal dominant disorders. The NF1 gene has a high rate of mutation, and half of cases are sporadic rather than familial.
The protein product, termed neurofibromin, is expressed in many tissues and belongs to a family of GTPase-activating proteins (GAPs), which inactivate ras protein.
NF1 is a classic tumor suppressor gene. Loss of GAP activity (in cells acquiring a second hit mutation) permits uncontrolled ras p21 activation, an effect that predisposes to the formation of benign neurofibromas.
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