NF glossary: terms to help understand neurofibromatosis

Neurofibromatosis (NF) is a genetic disorder. There are a few different types, which can cause a variety of different signs and symptoms ranging from benign changes in skin pigmentation, to developmental abnormalities, to disabling neurological symptoms. Knowing the terminology surrounding this disorder can be helpful to patients and caregivers of patients. With that in mind, the following are some key terms to help understand NF.

Neurofibromatosis type 1 (NF1). This is the most common type of NF. Signs and symptoms may be present at birth or develop during the first years of a person’s life. Other names include von Recklinghausen's disease and von Recklinghausen's neurofibromatosis. NF1 is caused by mutations to the neurofibromin 1 gene.

Tumor suppressor genes. These genes provide the body with instructions for making proteins that help control the growth and division of cancer cells (tumor suppressor proteins). NF is caused by mutations to tumor suppressor genes.

Cafe-au-lait macules (CALMs). Also called “cafe-au-lait spots.” These are one of the pigmentation changes caused by NF. CALMs are small, darkened areas of skin that resemble birthmarks. Having multiple CALMs can be a sign of NF1 or another type of NF. Freckling in unusual areas of the body (such as the underarms or groin) is another pigmentation change seen in people with NF.

Neurofibromas. These are benign tumors that grow on nerves and are a characteristic symptom NF1. Neurofibromas can occur close to the surface of the body and may be felt as lumps under the skin. They can also occur deeper within the body.

Plexiform neurofibroma (PN). These are large neurofibromas that involve multiple nerves. PNs can grow large and pose a significant health risk. PNs are more likely to become malignant than smaller neurofibromas.

Malignant peripheral nerve sheath tumors (MPNST). In up to 15 percent of cases, neurofibromas transform into cancerous tumors called malignant peripheral nerve sheath tumors. Pain, weight loss, night sweats, spasms, weakness in the affected area, and a mass that grows in size are symptoms of MPNST.

Lisch nodules. These are deposits of pigment in the iris of the eye. They are associated with NF1 and do not cause any problems or symptoms.

Glioma. This is a type of nerve tumor that occurs in the glial cells in the brain and spinal cord. Gliomas are more common in people with NF1, particularly optic pathway gliomas (OPGs), which occur in the nerves that connect the eyes and brain. OPGs can cause visual impairment.

Scoliosis. This is the clinical term for the abnormal lateral curvature of the spine and is one of several skeletal deformities that are associated with NF1. Others include a larger than average head size and bowing of the bones of the lower legs.

Neurofibromatosis type 2 (NF2). Less common than NF1, this type is caused by a different genetic mutation. The most common initial symptoms are hearing impairment, and/or tinnitus caused by tumors on the auditory nerves called vestibular schwannomas. People may also experience problems with balance and walking. Other symptoms can include dizziness, headache, facial weakness, numbness, or pain. NF2 typically has a later onset than NF1 and is caused by mutations to the neurofibromin 2 gene.

Cataracts. NF2 is associated with a number of vision impairments, including early onset cataracts. Cataracts are cloudy areas on the lens of the eye that can occur due to aging or injury, and after eye surgery. In people with NF2, cataracts can occur at much younger ages.

Schwannomas. Tumors of the Schwann cells. Schwann cells form myelin, the tissue that makes up the nerve sheath—the layer of tissue that insulates nerve fibers. Vestibular schwannomas are one example.

Schwannomatosis. A third and rare type of NF, characterized by the growth of schwannomas. It often causes intense pain. Onset is typically in adulthood, but schwannomatosis also affects teens and young adults. Unlike NF2, the auditory nerves are unaffected (at least initially). This type is known to be caused by mutations to the SMARCB1 and LZTR1 genes, but may be caused by other genetic mutations that are not yet identified.