Mosaic neurofibromatosis 1 in Adult
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
Differential Diagnosis & Pitfalls
- Familial café au lait macules– Patients will have multiple café au lait macules without other stigmata of neurofibromatosis. This condition will have a family history, whereas segmental neurofibromatosis typically does not.
- LEOPARD syndrome – Will include many additional features not seen in segmental neurofibromatosis, including ECG abnormalities, hypertelorism, abnormal genitalia, growth retardation, and deafness.
- Neurofibromatosis type 2 – A hallmark of this disease is schwannomas, 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 complex – 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.
- Nevus spilus (NS) – A large lesion that may resemble MNF1.
- Segmental speckled and lentiginous nevus
- Segmental agminated melanocytic nevi
- Phakomatosis pigmentokeratotica
- Blaschkoid eccrine spiradenomas