Reinhard E. Friedrich

Molecular study of frequency of mosaicism in neurofibromatosis 2 patients with bilateral vestibular schwannomas

Neurofibromatosis 2 (NF2) is a severe autosomal dominant disorder that predisposes to multiple tumours of the nervous system. About half of all patients are founders with clinically unaffected parents. The purpose of the present study was to examine the extent to which mosaicism is present in NF2 founders. A total of 233 NF2 founders with bilateral vestibular schwannomas (BVS) were screened by exon scanning. NF2 mutations were detected in the blood samples of 122 patients (52%). In 10 of the 122 cases, the ratio of mutant to normal alleles was obviously less than 1, suggesting mosaicism. Tumour specimens were available from 35 of the 111 subjects in whom no mutation could be detected in blood specimens. Mutational analysis by exon scanning detected typical NF2 mutations in 21 of the 35 tumours. In nine subjects, the alterations found in tumours could be confirmed to be the constitutional mutation based on finding of identical mutations in pathologically and/or anatomically distinct second tumours. In six other subjects with only a single tumour available, allelic loss of the NF2 gene was found in addition to the mutation in each tumour, suggesting that either the mutation or the deletion of the NF2 gene is probably the constitutional genetic alteration. Our results suggest that failure to find constitutional mutations in blood specimen from these 15 patients was not because of the limitation of the applied screening technique, but the lack of the mutations in their leucocytes, best explained by mosaicism. Extrapolating the rate (15/35 = 43%) of mosaicism in these 35 cases to the 111 NF2 founders with no constitutional NF2 mutations found in their blood, we inferred 48 mosaic subjects (111 × 0.429). Adding the 10 mosaic cases detected directly in blood specimens, we estimate the rate of mosaicism to be 24.8% (58/233) in our cohort of 233 NF2 founders with bilateral vestibular schwannomas.

Loss of NF1 allele in schwann cells but not in fibroblasts derived from an NF1‐associated neurofibroma

Neurofibromas, the hallmark of neurofibromatosis 1, are composed mainly of Schwann cells and fibroblasts. Inactivation of both NF1 alleles is the cause of these benign tumors, but it is unknown which cell type is the progenitor. In this study, we selectively cultured Schwann cells from an NF1‐associated neurofibroma. Fibroblasts were also obtained by culturing the tumor cells under standard conditions. Using four intragenic markers, we genotyped the NF1 locus in the original tumor and in the derived Schwann cells and fibroblasts. Loss of heterozygosity for two informative markers, which indicates loss of one NF1 allele, was found in Schwann cells but not in fibroblasts. This result suggests that genetic alterations of the NF1 gene in Schwann cells are responsible for the development of neurofibromas. Genes Chromosomes Cancer 24:283–285, 1999.

Clinical characterisation of 29 neurofibromatosis type-1 patients with molecularly ascertained 1.4 Mb type-1 NF1 deletions

Background Large deletions of the NF1 gene region occur in ∼5% of patients with neurofibromatosis type-1 (NF1) and are associated with particularly severe manifestations of the disease. However, until now, the genotype–phenotype relationship has not been comprehensively studied in patients harbouring large NF1 gene deletions of comparable extent (giving rise to haploinsufficiency of the same genes). Method We have performed the most comprehensive clinical/neuropsychological characterisation so far undertaken in NF1 deletion patients, involving 29 patients with precisely determined type-1 NF1 (1.4 Mb) deletions. Results Novel clinical features found to be associated with type-1 NF1 deletions included pes cavus (17% of patients), bone cysts (50%), attention deficit (73%), muscular hypotonia (45%) and speech difficulties (48%). Type-1 NF1 deletions were found to be disproportionately associated with facial dysmorphic features (90% of patients), tall stature (46%), large hands and feet (46%), scoliosis (43%), joint hyperflexibility (72%), delayed cognitive development and/or learning disabilities (93%) and mental retardation (IQ<70; 38%), as compared with the general NF1 patient population. Significantly increased frequencies (relative to the general NF1 population) of plexiform neurofibromas (76%), subcutaneous neurofibromas (76%), spinal neurofibromas (64%) and MPNSTs (21%) were also noted in the type-1 deletion patients. Further, 50% of the adult patients exhibited a very high burden of cutaneous neurofibromas (N≥1000). Conclusion These findings emphasise the importance of deletion analysis in NF1 since frequent monitoring of tumour presence and growth could potentiate early surgical intervention thereby improving patient survival.

Prognostic relevance of FDG PET in patients with neurofibromatosis type-1 and malignant peripheral nerve sheath tumours

PurposeIn patients with neurofibromatosis type-1 (NF1) and malignant peripheral nerve sheath tumours (MPNSTs), survival rates are low and time to death is often less than 2 years. However, there are patients with a more favourable prognosis who develop metastases rather late or not at all. Since histopathology and tumour grading are not well correlated with prognosis, we aimed to evaluate the potential of 18F-fluorodeoxyglucose positron emission tomography (FDG PET) for prediction of patient outcome in MPNST.MethodsFDG PET was performed in 16 patients with NF1 and MPNSTs. Standardised uptake values (SUVs) were calculated for each tumour and correlated to tumour grade and patient outcome in terms of survival or death.ResultsThree patients with tumour grade II had an SUV <3. None of these patients developed metastases or died during a follow-up of 41–62 months. Thirteen patients with tumour grades II and III had an SUV >3. Only one of these patients is still alive after 20 months; the remaining 12 died within 4–33 months. SUV predicted long-term survival with an accuracy of 94%, compared with 69% for tumour grade. In Kaplan-Meier survival analysis, patients with an SUV >3 had a significantly shorter mean survival time, 13 months, than patients with an SUV <3, in whom the mean survival time was 52 months. Tumour grading did not reveal differences in survival time (15 vs 12 months).ConclusionTumour SUV obtained by FDG PET was a significant parameter for prediction of survival in NF1 patients with MPNSTs while histopathological tumour grading did not predict outcome.

Bevacizumab induces regression of vestibular schwannomas in patients with neurofibromatosis type 2

Bilateral vestibular schwannomas are the hallmark of neurofibromatosis type 2 (NF2), and these tumors impair hearing and frequently lead to deafness. Neurosurgical intervention, the only established treatment, often damages the vestibular nerve. We report 2 cases in which treatment with bevacizumab (for 3 months in one case and 6 months in the other) induced regression of progressive vestibular schwannomas by more than 40% and substantially improved hearing in the patient treated for 6 months. Bevacizumab therapy may thus provide an effective treatment for progressive vestibular schwannomas in patients with NF2.

MRI growth patterns of plexiform neurofibromas in patients with neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder with an incidence of 1:3000. Approximately 30% of NF1 patients develop plexiform neurofibromas (PNF) which often cause severe clinical deficits. We studied the growth patterns of 256 plexiform neurofibromas (PNF) by magnetic resonance imaging (MRI) and associated disfigurement and functional deficits to determine whether there are definable growth types of these tumors. Retrospectively, we evaluated MRI scans obtained during 1997 to 2003 of 256 plexiform neurofibromas from 202 patients with NF1. Clinical investigation was carried out at the same time as the MRI scans. We identified three growth patterns: superficial in 59, displacing in 76, and invasive growth in 121 tumors. The majority (52%) of invasive PNF were found in the face, head and neck area. While superficial PNF primarily caused aesthetic problems, displacing PNF led in most cases to aesthetic problems and pain, while invasive PNF led mainly to functional deficits and disfigurement. Our study demonstrates that PNF have different growth patterns that are associated with specific clinical features. Classification of PNF may open new opportunities in clinical management, especially regarding decisions and options associated with surgical intervention.

Longitudinal study of neurofibromatosis 1 associated plexiform neurofibromas

Background: Plexiform neurofibromas are benign tumours that occur in more than half of people with neurofibromatosis 1 (NF1). These tumours can cause serious complications and can also progress to malignant peripheral nerve sheath tumours (MPNSTs), one of the leading causes of death among NF1 patients. Plexiform neurofibromas are clinically heterogeneous, and knowledge of their natural history is limited. In order to characterise the growth of plexiform neurofibromas better, we performed serial magnetic resonance imaging (MRI) in NF1 patients with such tumours. Methods: MRI was done on 44 plexiform neurofibromas in 34 NF1 patients (median age 10 years; range 1–47 years). Each tumour was measured in two dimensions from the MRI scan, and the area and growth rate were calculated. The median length of follow-up was 6 years, with an average interval of 3 years between scans. Results: 36 tumours remained stable in size throughout the period of follow-up. 8 tumours increased in size; all occurred in patients who were under 21 years of age when first studied. The single exception was a man who developed rapid tumour growth and pain in a plexiform neurofibroma that had been followed for 10 years. Biopsy showed the presence of an MPNST. Conclusion: Longitudinal MRI is a valuable means of monitoring the growth of plexiform neurofibromas in individuals with NF1.

Allelic loss of the NF1 gene in NF1-associated plexiform neurofibromas.

Neurofibromatosis 1 (NF1) is an autosomal dominant disorder with a complex variety of clinical symptoms. Genetic alteration of the NF1 gene on 17q11.2 is the disease. Neurofibromas of the peripheral nervous system are one main manifestation. A variant of neurofibroma is the plexiform neurofibroma which can be found in about 30% of NF1-patients, often causing severe clinical symptoms. In this study, we examined 14 such tumors from 10 NF1-patients for allele loss of the NF1 gene (LOH: loss of heterozygosity) using four intragenic polymorphic markers. Loss of heterozygosity was found in eight tumors from five patients, and suspected in one additional tumor from another patient. This finding suggests that loss of the second allele, and thus inactivation of both alleles of the NF1 gene, is associated with the development of plexiform neurofibromas. The 14 plexiform neufibromas were also examined for mutation in the TP53 gene by screening exons 5 through 8 using temperature gradient gel electrophoresis. No mutation was found in any of the tumors.

Bone health and fracture rate in individuals with neurofibromatosis 1 (NF1)

Background: Patients with neurofibromatosis 1 (NF1) are shorter than expected and often have low bone mineral density (BMD), but the pathogenesis of these bony problems is poorly understood. Methods: We performed an exploratory study of BMD, 18 laboratory measures of bone metabolism, and fracture history in 72 adult NF1 patients. Results: Eight of the 18 clinical biochemical measures of bone health had at least 10% of NF1 patients outside the standard reference range. Serum 25-hydroxy-vitamin D concentrations were low in 56% of the NF1 patients, serum parathyroid hormone (PTH) concentrations were high in 34%, and urine deoxypyridinoline cross-link concentrations were high in 50%. Mean serum 25-hydroxy-vitamin D concentrations were significantly lower in people with NF1 than in season matched controls in both summer (p = 0.008) and winter (p<0.001). 36 (50%) of the 72 people with NF1 studied had BMD consistent with osteopenia, and 14 (19%) had BMD consistent with osteoporosis. High serum PTH concentration, high serum bone tartrate resistant acid phosphatase concentration, and high serum calcium concentration were associated with lower BMD among the NF1 patients. Males were more likely than females to have low BMD. The reported frequency of fractures in individuals with NF1 was much higher than in their unaffected siblings and spouses (p<0.001), and pathological fractures were reported only in NF1 patients. Conclusion: People with NF1 often have a generalised abnormality of bone metabolism. Further studies are needed to determine the biochemical and molecular basis of this abnormality.

Vitamin D deficiency associated with number of neurofibromas in neurofibromatosis 1

Neurofibromatosis 1 (NF1) is a tumour suppressor gene syndrome characterized by multiple cutaneous and plexiform neurofibromas. Focal osseous abnormalities, short stature, and decreased bone mineral density are also frequent in people with NF1. We measured serum 25-hydroxyvitamin D concentrations in 55 patients with NF1 and 58 healthy controls, and correlated the findings in the patients with NF1 with their estimated number of dermal neurofibromas. Geometric mean (SD) serum 25-hydroxyvitamin D concentration was 14.0 (1.6) ng/mL among the patients with NF1 compared with 31.4 (1.7) ng/mL among healthy controls (p<<0.0001). The serum vitamin D concentration and number of dermal neurofibromas reported by patients with NF1 were inversely correlated (Spearman’s ρ = −0.572, p<0.00001). The occurrence of low serum vitamin D concentrations in people with NF1, especially those with many dermal neurofibromas, may provide new pathogenic insights and have important therapeutic implications.