Neurofibromatosis 1 (NF1)

NF1 is one of the most common neurogenetic conditions, affecting about 100,000 children and adults in the U.S.1,2 The most common sign is pigmented skin lesions called café-au-lait macules. People with NF1 can also develop tumors in the brain and along the nerves. 

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NF1 is one of the most common neurogenetic conditions, affecting about 100,000 children and adults in the U.S.1,2 The most common sign is pigmented skin lesions called café-au-lait macules. People with NF1 can also develop tumors in the brain and along the nerves. 

NF1 is an autosomal dominant neurocutaneous disorder caused by mutations in the NF1 tumor suppressor gene. Highly variable expressivity, progression of phenotypic characteristics over time, and a 50% de novo mutation rate can make it challenging to establish a clinical diagnosis, particularly in young children. In these situations, molecular genetic testing can be useful.

Disease Name 
Neurofibromatosis 1
von Recklinghausen disease
Disease Information 

NF1 is characterized by abnormal pigmentation of the skin and eyes, multiple nerve sheath tumors, bone abnormalities, learning disabilities, vascular malformations, and an increased risk of breast cancer in women.3,4,5 Signs of NF1 can be present at birth or appear in the first several years of life. Clinical diagnostic criteria for NF1 have been developed by the National Institutes of Health (NIH)6 and are met in an individual with two or more of the following:

1. Six or more café-au-lait macules greater than 5mm diameter in prepubertal individuals, and 15mm in diameter in postpubertal individuals

2. Two or more neurofibromas of any type, or one plexiform neurofibroma

3. Skin fold freckling in the axillary and/or inguinal regions

4. Optic pathway glioma

5. Two or more Lisch nodules (iris hamartomas)

6. Distinct osseous lesion (e.g. sphenoid dysplasia, tibial pseudoarthrosis)

7. A first-degree relative (parent, sibling, child) with NF1, as defined by the above criteria

Additional clinical features can include cardiovascular malformations, juvenile xanthogranuloma, pheochromocytoma, neovascular glaucoma, osteopenia, scoliosis, diffuse polyneuropathy, seizures, and hypotonia.5 Learning disabilities and attention deficit hyperactivity disorder (ADHD) are frequent, occurring in over half of affected individuals.3 A possible association between NF1 and autism spectrum disorders has also been reported.7 While most NF1-related tumors are benign, there is an approximately 10-12% lifetime risk of malignant conversion of plexiform neurofibromas5. High grade brainstem gliomas in the setting of NF1 have also been reported.5

NF1 is a progressive disorder exhibiting an increase in number and significance of clinical features across the lifespan. The penetrance of NF1 mutations approaches nearly 100% by adulthood, and the NIH clinical criteria are both highly specific and sensitive in adults with NF1.5 Clinical signs vary greatly between affected individuals, even between family members with the same mutation. Though café-au-lait macules are the most common features of NF1, they are not present in every affected individual.

NF1 is a member of the Ras subfamily, a group of related proteins involved in cellular signal transduction.9 Ras proteins have been implicated in many types of cancer. NF1 encodes for neurofibromin, which appears to be a negative regulator of the Ras/MAP kinase pathway. Signaling through this pathway is important for the neurotrophin-induced differentiation of neuronal and neuroblastoma cells.10

Related Phenotypes

Some individuals have characteristics of NF1 restricted to one part of the body, known as segmental or regional NF1. In some cases, the unusual distribution has occurred by chance alone. In others, the segmental pattern represents somatic mosaicism for an NF1 mutation.11

Approximately 12% of those with NF1 have a Noonan syndrome phenotype, with features that can include hypertelorism, down-slanted palpebral fissures, low-set ears, neck webbing, and pulmonic stenosis.12 Most people with an NF1-Noonan phenotype have a mutation in NF1.13 Some may have a chance co-occurrence of both NF1 and Noonan syndrome.

Some individuals presenting with café-au-lait macules and skin fold freckling have Legius syndrome rather than NF1. Other typical NF1 findings, such as neurofibromas, optic gliomas, and Lisch nodules are not a part of the Legius syndrome phenotype.14 Sequential genetic testing for NF1 and SPRED1 is often initiated for individuals with skin characteristics of NF1 and no other clinical manifestations, and can assist in clarifying the diagnosis.

Testing Benefits & Indication 

Genetic testing is useful for diagnostic confirmation in symptomatic individuals, and for testing of at-risk asymptomatic family members (including prenatal diagnosis). Molecular confirmation of a diagnosis may help avoid unnecessary testing and procedures, as well as guide recommendations for medical treatment and screening. Increased surveillance for a variety of clinical features is recommended for those found to harbor an NF1 mutation.

NF1 analysis is recommended for any of the following:15

- Any patient meeting clinical diagnostic criteria for NF1 for whom genetic confirmation would assist with enrollment on clinical trials, family planning, or other management decisions

- Any individual with suspected NF1 who does not yet meet the clinical diagnostic criteria

- Any individual with a family history of NF1

Test Description 

NF1 coding exons 1-58 and well into the 5’ and 3’ ends of all the introns and untranslated regions are analyzed by sequencing. Gross deletion/duplication analysis determines gene copy number for coding exons 1-58. Clinically significant intronic findings beyond 5 base pairs are always reported. Intronic variants of unknown or unlikely clinical significance are not reported beyond 5 base pairs from the splice junction. Genomic deoxyribonucleic acid (gDNA) is isolated from the patient’s specimen using standardized methodology and quantified. Sequence enrichment of the targeted coding exons and adjacent intronic nucleotides is carried out by a bait-capture methodology, using long biotinylated oligonucleotide probes followed by polymerase chain reaction (PCR) and next generation sequencing (NGS). Sanger sequencing is performed for any regions missing or with insufficient read depth coverage for reliable heterozygous variant detection. Reportable small insertions and deletions, potentially homozygous variants, variants in regions complicated by pseudogene interference, and single nucleotide variant calls not satisfying 100x depth of coverage and 40% het ratio thresholds are verified by Sanger sequencing.20  Gross deletion/duplication analysis of NF1 using the multiplex ligation-dependent probe amplification (MLPA) kit is also performed.

Mutation Detection Rate 

~65% of people with NF1 will have a detectable mutation in NF1 using gene sequence and deletion/duplication analysis (clinical sensitivity).17-19 Ambry's NF1 analysis can detect ~65% of described mutations in the gene, when present (analytic sensitivity).

Specimen Requirements 

Complete specimen requirements are available here or by downloading the PDF found above in the Quick Links section at the top of this page.

Prenatal testing is available. 

Turnaround Time 
TEST CODE TECHNIQUE TURNAROUND TIME (weeks)
5704 NF1 Gene Sequence and Deletion/Duplication Analysis 2-3 
5730 NF1 Gene Sequence and Deletion/Duplication Analysis,
with reflex to SPRED1 Gene Sequence and
Deletion/Duplication Analysis
3-4 

 

Specialty 
Genes 
NF1
References 
  1. Lammert M, et al. Prevalence of neurofibromatosis 1 in German children at elementary school enrollment. Arch Dermatol. 2005;141:71–74.
  2. Evans DG, et al. Birth incidence and prevalence of tumor-prone syndromes: estimates from a UK family genetic register service. Am J Med Genet A. 2010;152A:327–332.
  3. Yohay K. Neurofibromatosis types 1 and 2. Neurologist. 2006;12(2):86-93.
  4. Madanikia SA, et al. Increased risk of breast cancer in women with NF1. Am J Med Genet A. 2012;158A(12):3056-3060.
  5. Ferner RE, et al. Neurofibromatosis type 1 (NF1): diagnosis and management. Handb Clin Neurol. 2013;115:939–955.
  6. NIH. National Institutes of Health Consensus Development Conference Statement: neurofibromatosis. Bethesda, MD, USA, July 13-15, 1987. Neurofibromatosis. 1988;1:172–178.
  7. Garg S, et al. Neurofibromatosis type 1 and autism spectrum disorder. Pediatrics. 2013;132(6):e1642-1648.
  8. Burkitt Wright EM, et al. Can the diagnosis of NF1 be excluded clinically? A lack of pigmentary findings in families with spinal neurofibromatosis demonstrates a limitation of clinical diagnosis. J Med Genet. 2013;50(9):606-613.
  9. Yohay KH. The genetic and molecular pathogenesis of NF1 and NF2. Semin Pediatr Neurol. 2006;13(1):21-26.
  10. Segal R. Selectivity in neurotrphin signaling: themes and variations. Ann Rev Neurosci. 2003;26:299-330.
  11. Messiaen L, et al. Mosaic type-1 NF1 microdeletions as a cause of both generalized and segmental neurofibromatosis type-1 (NF1). Hum Mutat. 2011;32:213–219.
  12. Colley A, et al. Neurofibromatosis/Noonan phenotype: a variable feature of type 1 neurofibromatosis. Clin Genet. 1996;49:59–64.
  13. De Luca A, et al. NF1 gene mutations represent the major molecular event underlying neurofibromatosis-Noonan syndrome. Am J Hum Genet. 2005;77:1092–1101.
  14. Stowe I, et al. A shared molecular mechanism underlies the human rasopathies Legius syndrome and Neurofibromatosis-1. Genes Dev. 2012; 26:1421-1426.
  15. Hersch JH, American Academy of Pediatrics Committee on Genetics. Health supervision for children with neurofibromatosis. Pediatrics. 2008;121(3):633-642.
  16. Mu W, et al. Sanger confirmation is required to achieve optimal sensitivity and specificity in next-generation sequencing panel testing. J Mol Diagn. 2016. 18(6):923-932.
  17. Fahsold R, et al. Minor lesion mutational spectrum of the entire NF1 gene does not explain its high mutability but points to a functional domain upstream of the GAP-related domain. Am J Hum Genet. 2000;66:790–818.
  18. Griffiths S, et al. Molecular diagnosis of neurofibromatosis type 1: 2 years’ experience. Fam Cancer. 2007;6:21–34.
  19. van Minkelen R, et al. A clinical and genetic overview of 18 years neurofibromatosis type 1 molecular diagnostics in the Netherlands. Clin Genet. 2014;85:318–27.
  20. Mu W, et al. Sanger confirmation is required to achieve optimal sensitivity and specificity in next-generation sequencing panel testing. J Mol Diagn. 2016. 18(6):923-932.