Segmental neurofibromatosis is considered to be the result of postzygotic NF1 gene mutations. We present a family in which the proband has generalized neurofibromatosis 1, whereas members of previous generations manifest segmental skin lesions. All, including the clinically asymptomatic grandmother, carry the same haplotype. This is the only case in the literature in which a parent with segmental skin findings has a child with full-blown neurofibromatosis 1 disease. The genetic mechanisms underlying this association are discussed. This family can be further investigated by examination of tissue samples from affected and unaffected sites for mutations.
Neurofibromatosis type 1 (NF1) is the most common neurogenetic disorder worldwide, caused by mutations in the (NF1) gene. Although NF1 is a single-gene disorder with autosomal-dominant inheritance, its clinical expression is highly variable and unpredictable. NF1 patients have the highest known mutation rate among all human disorders, with no clear genotype-phenotype correlations. Therefore, variations in NF1 mutations may not correlate with the variations in clinical phenotype. Indeed, for the same mutation, some NF1 patients may develop severe clinical symptoms whereas others will develop a mild phenotype. Variations in the mutant NF1 allele itself cannot account for all of the disease variability, indicating a contribution of modifier genes, environmental factors, or their combination. Considering the gene structure and the interaction of neurofibromin protein with cellular components, there are many possible candidate modifier genes. This review aims to provide an overview of the potential modifier genes contributing to NF1 clinical variability.
Spinal tumours are observed in about 40% of neurofibromatosis type 1 (NF1) patients and occur within two subgroups: (1) NF1 patients carrying classical diagnostic criteria and only one or few spinal tumours and (2) patients with few NF1 stigmata but multiple bilateral spinal tumours, an entity called spinal neurofibromatosis. We report a young patient whose classical NF1 stigmata and numerous spinal neurofibromas matched both groups. He carried a single base deletion, c.389delA in exon 4a, which creates a premature termination at codon 164. This case illustrates the possibility of variant phenotypes and a novel NF1 mutation associated with spinal neurofibromatosis.
Forty-four classical PKU patients have been screened for various mutations. The newly identified IVS 10 splicing mutation was found in 32% of the mutant alleles and comprises 74-5% of the mutations that could be typed: 261arg-gln (6-8%), 158arg-gly (2.3%) 252arg-trp (1P1%), 2809gu-lYs (-), and 272g1y-s'oP (-) were the other mutations that were screened.
Neurofibromatosis 1 is an autosomal dominant disorder. Noonan's syndrome is known to be associated with neurofibromatoses. Patients with neurofibromatosis are predisposed to developing malignant tumors. The relationship between the genetic changes in the neurofibromin gene and mechanisms associated with tumor development in neurofibromatosis has been investigated. A non-sense mutation C2446T --> R816X of the neurofibromin gene has been detected in some patients with the neurofibromatosis 1-Noonan's syndrome phenotype. We describe a case of an infant with the overlapping features of neurofibromatosis 1 and Noonan's syndrome who presented with rhabdomyosarcoma of the urinary bladder. The genetic analysis of our patient revealed neither mutation in the neurofibromatosis 1-guanosine triphosphatase-activating protein-related domain nor the R816X nonsense mutation. The phenotypic and genotypic features of neurofibromatosis, Noonan's syndrome, and cases with the overlapping features of both syndromes have been reviewed. The presentation of our case underlines the importance of careful examination for the clinical features of neurofibromatosis and phenotypic traits of associated diseases, especially in patients with malignant tumors.
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