title: A quantitative assessment of the burden and distribution of Lisch nodules in adults with neurofibromatosis type 1.
abstract: OBJECTIVE
  The presence of two or more Lisch nodules (melanocytic hamartomas of the iris) is one of seven diagnostic criteria for neurofibromatosis type 1 (NF1), a common monogenic disorder of dysregulated neurocutaneous growth. The hypothesis that Lisch nodules arise secondary to exposure to ultraviolet (UV) radiation from sunlight was investigated.
  
  
  METHODS
  Lisch nodule burden was mapped and quantified in the irides of 77 adults with NF1. Lifetime sunlight (UV radiation) exposure was inventoried, NF1 neurocutaneous severity determined, and two NF1 mutations predictive of severity selectively genotyped.
  
  
  RESULTS
  There was high interindividual variability in Lisch nodule burden. Lisch nodules were primarily located in the inferior hemifield (half) of the iris, regardless of its color (P = 3.0 x 10(-20)). Light irides harbored significantly more Lisch nodules than dark irides (P = 4.8 x 10(-5)). There was no statistically significant correlation of Lisch nodule burden to lifetime sunlight exposure "dose" or NF1 neurocutaneous severity.
  
  
  CONCLUSIONS
  The difference in Lisch nodule burden between the superior and inferior iris hemifields is most likely due to the sunlight-shielding effects on the superior half by periocular structures. The difference in Lisch nodule burden between light and dark irides is probably due to the photoprotective effects of pigmentation. The genes underlying the control of iris color may thus be viewed as modifiers of severity of Lisch nodule burden in NF1. Given the role of UV radiation and, presumably, DNA damage in Lisch nodule pathogenesis, "benign tumor of the iris," not "hamartoma," may be a better descriptor.
authors.affiliation: Penn State University College of Medicine, Hershey, Pennsylvania, USA.
authors.forename: Sean
authors.initials: S
authors.lastname: Boley
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Sloan
authors.forename: Alexander
authors.initials: A
authors.lastname: Pemov
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Stewart
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005127:Eye Color; D005260:Female; D016514:Genes, Neurofibromatosis 1 / Q000502:physiology; D005838:Genotype; D006222:Hamartoma / Q000209:etiology* / Q000235:genetics / Q000473:pathology; D006801:Humans; D007498:Iris / Q000473:pathology / Q000528:radiation effects*; D015811:Iris Neoplasms / Q000209:etiology* / Q000235:genetics / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009381:Neoplasms, Radiation-Induced / Q000209:etiology* / Q000235:genetics / Q000473:pathology; D009456:Neurofibromatosis 1 / Q000209:etiology* / Q000235:genetics / Q000473:pathology; D020641:Polymorphism, Single Nucleotide; D012878:Skin Neoplasms / Q000209:etiology* / Q000235:genetics / Q000473:pathology; D013472:Sunlight; D011795:Surveys and Questionnaires; D047368:Tumor Burden; D014466:Ultraviolet Rays / Q000009:adverse effects; D055815:Young Adult