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Mosaic neurofibromatosis 1 in Infant/Neonate
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Mosaic neurofibromatosis 1 in Infant/Neonate

Contributors: David O'Connell MD, Belinda Tan MD, PhD, Susan Burgin MD
Other Resources UpToDate PubMed


Mosaic neurofibromatosis 1 (MNF1) or mosaic neurofibromatosis (previously designated as neurofibromatosis type V and segmental neurofibromatosis), is a segmental or quasi-segmental phenotype of NF1 caused by a postzygotic mutation of the NF1 gene, resulting in mosaicism. Patients with this condition lack a family history of the disease. MNF1 presents with features of NF1 in localized areas of the body. It may involve one segment only (localized) or multiple segments, even in up to half the body (generalized). It can be either symmetrical or asymmetrical depending on the cell lines affected and the timing of the mutation. The incidence is estimated to be 1 in 36 000-40 000 but is likely higher as it is probably underreported.

MNF1 results from a mutation of the NF1 gene located on the long arm of chromosome 17. This gene locus encodes for neurofibromin, which functions as a tumor suppressor gene. Clinically, the most common signs of MNF1 are pigmentary changes (café au lait macules, freckling, diffuse background pigment), cutaneous neurofibromas, and plexiform neurofibromas. Lisch nodules and optic gliomas are uncommon. While up to 30% of patients with MNF1 will have extracutaneous manifestations of NF1, including hypertension, learning disabilities, and seizures, patients with MNF1 will generally have milder clinical manifestations and fewer generalized complications compared to those with inherited NF1.

It is important to note that gonadal mosaicism can occur in MNF1 even in the absence of inguinal freckling, resulting in a small but real risk of complete NF1 in some offspring.


Q85.00 – Neurofibromatosis, unspecified

1010653007 – Segmental neurofibromatosis type 1

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Differential Diagnosis & Pitfalls

  • Familial café au lait macules– Patients will have multiple Café au lait spot without other stigmata of neurofibromatosis. This condition will have a family history, whereas segmental neurofibromatosis typically does not.
  • Multiple lentigines syndrome – Will include many additional features not seen in segmental neurofibromatosis, including ECG abnormalities, hypertelorism, abnormal genitalia, growth retardation, and deafness.
  • Neurofibromatosis – A hallmark of this disease is Neurilemmoma, which are not present in segmental neurofibromatosis.
  • Legius syndrome – Autosomal dominant inheritance; may also have freckling; does not have NFs, Lisch nodules, or optical gliomas.
  • McCune-Albright syndrome – Polyostotic fibrous dysplasia; endocrine gland hyperfunction; may follow lines of Blaschko.
  • Tuberous sclerosis – Autosomal dominant inheritance; CALMs may be present, but hallmark is hypopigmented macules; facial angiofibromas and ungual fibromas; Shagreen patch.
  • Partial unilateral lentiginosis (PUL) – Usually sharp cutoff at midline; may coexist with MNF1.
  • Speckled lentiginous nevus (NS) – A large lesion that may resemble MNF1.
  • Segmental Speckled lentiginous nevus
  • Segmental Agminated nevusi
  • Phakomatosis pigmentokeratotica
  • Blaschkoid Eccrine spiradenoma

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Last Reviewed:01/12/2022
Last Updated:01/13/2022
Copyright © 2024 VisualDx®. All rights reserved.
Mosaic neurofibromatosis 1 in Infant/Neonate
A medical illustration showing key findings of Mosaic neurofibromatosis 1 : Intertriginous distribution, Tumor, Unilateral distribution, Smooth papules, Smooth nodules, Dermatomal distribution
Clinical image of Mosaic neurofibromatosis 1 - imageId=92354. Click to open in gallery.  caption: 'Numerous light brown macules and patches (cafe au lait macules) in a cluster on the left lower back.'
Numerous light brown macules and patches (cafe au lait macules) in a cluster on the left lower back.
Copyright © 2024 VisualDx®. All rights reserved.