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Key Points

  • Disease summary:

    • Neurofibromatosis type 1 (NF1) is a common (∼1/3000), progressive neurocutaneous disorder primarily of increased tumor predisposition, but also pigmentary abnormalities, osseous dysplasia, and impaired cognitive function that arises secondary to mutations in the tumor suppressor gene NF1.

    • NF1 is a pleiotropic disorder, affecting different organ systems (central and peripheral nervous systems, bone, vasculature) with wide variation in severity of clinical features, even among members of the same family. There is limited genotype-phenotype correlation (see Counseling).

    • NF1 affects all ethnic groups and both sexes equally.

    • As a population, individuals with NF1 have a reduced lifespan.

  • Hereditary basis:

    • NF1 is a monogenic disorder with an autosomal dominant pattern of inheritance. It is 100% penetrant, typically by late adolescence. Approximately half of the individuals affected with NF1 have a family history of the disorder.

  • Differential diagnosis:

    • The diagnosis is rarely mistaken in a patient with numerous café-au-lait macules, neurofibromas, and axillary freckling. Certain features, especially when present in isolation or in a younger patient, may present a diagnostic challenge (Table 108-1). Consideration of a missense NF1 mutation, or a de novo NF1 mutation present in a segmental or mosaic state (see Counseling) should be made when confronted with either café-au-lait macules only or neurofibromas only, especially in a limited distribution. A diagnosis of Legius syndrome should be considered in older individuals with pigmentary findings only and absence of neurofibromas.

Table 108-1Differential Diagnosis of Isolated Disease Features in NF1

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