Neurofibromatosis Type 1 Genetic Testing

About this condition

Neurofibromatosis Type 1

Neurofibromatosis Type 1 is caused by inherited pathogenic variants in NF1, a large gene (350 kb, 60 exons) encoding neurofibromin — a regulator of the RAS signaling pathway. RAS controls cell growth, proliferation, and differentiation. Neurofibromin normally acts as a brake on RAS signaling; pathogenic NF1 variants eliminate this brake, allowing constitutive RAS activation. The result is widespread tumor formation including café-au-lait macules, cutaneous and subcutaneous neurofibromas, optic pathway gliomas, plexiform neurofibromas, and malignant peripheral nerve sheath tumors (MPNST). Penetrance is virtually complete — 100% of NF1 carriers show some clinical features — yet expressivity is highly variable, sometimes dramatically so even within families.

Neurofibromatosis Type 1 affects approximately 1 in 3,000 people worldwide, making it one of the most common autosomal dominant genetic disorders. Approximately 50% of cases are de novo variants, without a family history. Over 3,000 distinct pathogenic variants have been catalogued across the NF1 gene, with no mutation hotspots — pathogenic mutations are distributed throughout the coding region. NF1 variants span multiple mutation types: point mutations, small insertions/deletions, splice-site variants, large deletions (including whole-gene microdeletions, which produce a more severe phenotype), and complex rearrangements. This extreme heterogeneity makes interpretation challenging without careful genetic assessment.

Identifying the specific NF1 variant has immediate medical implications. Whole-gene deletions predict more severe disease including higher risk of MPNST and intellectual disability — enabling accelerated surveillance in these higher-risk carriers. A confirmed NF1 diagnosis triggers eligibility for MEK inhibitor therapy (selumetinib) — FDA-approved specifically for inoperable plexiform neurofibromas, directly targeting the RAS pathway dysregulation caused by NF1 loss. Genetic confirmation enables cascade testing of at-risk relatives and prenatal/preimplantation genetic diagnosis for family planning.

NF1 genotype-phenotype correlation is strong: whole-gene deletions predict more severe disease and higher MPNST risk, requiring intensified surveillance compared to point-mutation carriers.

Gene locus: NF1 (17q11.2)

The NF1 gene is notoriously difficult to sequence. Standard panels miss whole-gene deletions, complex rearrangements, and mosaic variants — which account for ~5% of NF1 cases.

NF1 sequencing is complicated by pseudogenes and structural variants

The NF1 gene is exceptionally large and difficult to sequence accurately. It contains numerous pseudogene segments on other chromosomes that complicate standard short-read sequencing. Approximately 5% of NF1 carriers have whole-gene deletions — complete loss of the entire NF1 locus — which require specialized copy number analysis beyond what standard targeted sequencing provides. Mosaic NF1 variants, present in only a fraction of blood cells, are missed by standard sequencing depth. Whole genome sequencing provides complete coverage including pseudogene-prone regions and detects structural variants and mosaic variants that targeted panels miss.

NF1 type determines disease severity and treatment eligibility

Genetic confirmation of NF1 enables genotype-phenotype counseling: carriers with whole-gene deletions should expect more severe disease, higher MPNST risk, and potential intellectual disability — triggering more aggressive tumor surveillance. All NF1 carriers with inoperable plexiform neurofibromas are now eligible for selumetinib (Koselugo), an FDA-approved MEK inhibitor that directly targets the RAS pathway pathologically activated by NF1 loss. A genetic finding enables family cascade testing, prenatal counseling, and informed transition planning into adulthood.

Your skin tells a story in spots and bumps before you understand what it means. A genetic answer exists — and changes what you plan for.