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Neurofibromatosis Type 1

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Neurofibromatosis Type 1

Neurofibromatosis is a group of genetic disorders

Overview

Neurofibromatosis is a group of genetic disorders, which cause an increased risk of abnormal growths of the nerve sheath (nerve sheath tumors). The nerve sheath is the tissue that wraps around the nerve cells (neurons) to provide insulation and protection.

Symptoms & Signs

Symptoms common in Neurofibromatosis type 1

  • Café au lait spots (neurofibromas):

A café au lait spot is a brown skin mark that can appear at birth or in early childhood. They arise from nerve cells. In children, café au lait spots are over 5 mm in diameter, and in adults, over 15 mm. People with Neurofibromatosis type 1 usually have more than 2 café au lait spots.

  • Plexiform neurofibromas: a bulging growth (tumor) of the nerve sheath cells, resembling a "bag of worms". It is most common on the eyelid, or around the eyeball. It is non-cancerous but can cause disfigurement, squint, and eyelid drop (ptosis).
  • Freckles: commonly in sun-exposed areas, and skin folds like the armpit (axillary), and the upper thigh crease (groin).

Eye symptoms:

  • Lisch nodules: harmless brown spots in the colored part of the eyes (iris) that can be detected with a microscopic examination (slit lamp exam).
  • Tumor of the optic nerve (Optic Glioma): a non-cancerous growth, which causes compression to the nerve which connects the eyes to the brain (optic nerve) and can affect vision.
  • Defect in the eye socket (sphenoid wing dysplasia): can lead to a bulging eyeball (exophthalmos) or sunken eyeball (enophthalmos).
  • A larger-than-normal head size (macrocephaly).
  • Below average height for age (short stature).
  • Learning disability and behavioral problems: social difficulties, attention deficit hyperactivity disorder (ADHD), autism, mood disorders.

Bone symptoms:

  • Abnormally curved spine (Scoliosis).
  • Humpback (Kyphosis).
  • Bowing of the leg bone (tibial dysplasia): in an outer and forward direction (anterolateral).
  • Non-union of long bones (pseudarthrosis): weak and malformed bones (such as the tibia) fracture due to minor trauma, and are unable to heal without surgical intervention (non-union).

Diagnosis

Neurofibromatosis Type 1 is diagnosed through a combination of clinical and genetic (molecular) criteria. The presence of an affected parent or family member with Neurofibromatosis Type 1 significantly increases the likelihood of diagnosis. In the case that multiple suggestive symptoms of Neurofibromatosis Type 1 are present, Single Gene Testing may be done to confirm the disease.

Treatment & Management

Management

  • A team of healthcare specialists should be involved in care, including:

Resources & Support

  • Eye specialist (ophthalmologist).
  • Brain and nerve specialist (neurologist).
  • Brain and spine surgeon (neurosurgeon).
  • Bone specialist (orthopedic surgeon).
  • Genetic counselor.
  • Learning disability specialist.

There are several types of Neurofibromatosis:

  • Neurofibromatosis Type 1.
  • Neurofibromatosis Type 2 (also known as NF2-related schwannomatosis).
  • Schwannomatosis (also known as non-NF2-related schwannomatosis).
  • Legius syndrome: a subset of Neurofibromatosis Type 1 in which there is no tumor development.

Inheritance

Neurofibromatosis Type 1 is inherited in an autosomal dominant manner.

  • “Autosomal” means that the gene in question is located on one of the numbered, or non-sex chromosomes.
  • “Dominant” inheritance means one gene in a pair being abnormal is enough to cause the disease.

The risk of reoccurrence of Neurofibromatosis Type 1 in other siblings

About 50% of individuals have an affected parent.
If one parent is affected, other siblings have a 50% chance of being affected with Neurofibromatosis Type 1.
About 50% of individuals have the disease because of a new (de novo) mutation.
If the child has Neurofibromatosis Type 1 due to a new mutation and have no other affected family members, the risk of other siblings being affected is less than 1%.

Prevalence

The estimated incidence of Neurofibromatosis Type 1 is 1 in every 3,000 live births, across different ethnic groups. The incidence among males and females is similar.

Credits

  • Written by: Khawla Ben Yahia, MBBS.
  • Reviewed by: Dr. Ayman W. El-Hattab, MD, FAAP, FACMG

References

  • Friedman, Jan M. "Neurofibromatosis 1." Gene reviews (2022).
  • Almuqbil, Mohammed, et al. "Epidemiology and Outcomes of Neurofibromatosis Type 1 (NF-1): Multicenter Tertiary Experience." Journal of Multidisciplinary Healthcare (2024): 1303-1314.
  • Lee, Tin-Suet Joan, et al. "Incidence and prevalence of neurofibromatosis type 1 and 2: a systematic review and meta-analysis." Orphanet Journal of Rare Diseases 18.1 (2023): 292.
  • Rijken, B. F. M., M. L. C. van Veelen-Vincent, and I. M. J. Mathijssen. "Sphenoid dysplasia in patients with neurofibromatosis type 1: Clinical features and imaging findings including cerebrospinal fluid alterations." European Journal of Paediatric Neurology 42 (2023): 28-33.
  • NIH. "Neurofibromatosis." National Institute of Neurological Disorders and Stroke (2024).
  • Gompertz, et al. "Neurofibromatosis type 1" NHS National Genomics Education Programme (2023).
  • Widmann, Doyle. "Orthopedic Complications of Neurofibromatosis Type 1: Scoliosis, Tibial Dysplasia and Other Issues" HSS (Hospital for Special Surgery) (2021).
  • Germanwala. "Neurofibromatosis" HSS (Hospital for Special Surgery) (2024).
  • NORD. "Neurofibromatosis 1." National Organization for Rare Disorders (2022).
  • M. Alkatan, Hind, et al. "Ocular Findings in Neurofibromatosis". Neurofibromatosis - Current Trends and Future Directions, IntechOpen, 20 May 2020. Crossref, doi:10.5772/intechopen.90021.

Disclaimer: This information is for educational purposes only and should not replace professional medical advice. Always consult with qualified healthcare providers for diagnosis and treatment.

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