Screening of potential novel candidate genes in schwannomatosis patients

Schwannomatosis comprises a group of hereditary tumor predisposition syndromes characterized by, usually benign, multiple nerve sheath tumors, which frequently cause severe pain that does not typically respond to drug treatments. The most common schwannomatosis‐associated gene is NF2, but SMARCB1 and LZTR1 are also associated. There are still many cases in which no pathogenic variants (PVs) have been identified, suggesting the existence of as yet unidentified genetic risk factors. In this study, we performed extended genetic screening of 75 unrelated schwannomatosis patients without identified germline PVs in NF2, LZTR1, or SMARCB1. Screening of the coding region of DGCR8, COQ6, CDKN2A, and CDKN2B was carried out, based on previous reports that point to these genes as potential candidate genes for schwannomatosis. Deletions or duplications in CDKN2A, CDKN2B, and adjacent chromosome 9 region were assessed by multiplex ligation‐dependent probe amplification analysis. Sequencing analysis of a patient with multiple schwannomas and melanomas identified a novel duplication in the coding region of CDKN2A, disrupting both p14ARF and p16INK4a. Our results suggest that none of these genes are major contributors to schwannomatosis risk but the possibility remains that they may have a role in more complex mechanisms for tumor predisposition.

Prenatal Detection of PIK3CA-related Overgrowth Spectrum in Cultured Amniocytes Using Long-range PCR and Next-generation Sequencing

Mutations in PIK3CA are associated with overgrowth spectrum disorders including excessive growth in some areas of the body and the central nervous system. Alterations in PIK3CA occur as somatic, postzygotic events and confer a mosaic genotype with variability in phenotypic expression being commonly observed. We describe the second reported prenatal diagnosis of a PIK3CA-related overgrowth spectrum disorder. The prenatal ultrasound features in this case enabled the presumptive, prospective diagnosis to be made which was then confirmed by genetic testing. Subsequent parental testing for mutations in PIK3CA demonstrated normal genotypes. Identification of this mutation prenatally enabled prospective information to be provided to the family and facilitated multidisciplinary perinatal management.

Revisiting neurofibromatosis type 2 diagnostic criteria to exclude LZTR1-related schwannomatosis

OBJECTIVE

To determine the specificity of the current clinical diagnostic criteria for neurofibromatosis type 2 (NF2) relative to the requirement for unilateral vestibular schwannoma (VS) and at least 2 other NF2-related tumors.

METHODS

We interrogated our Manchester NF2 database, which contained 205 individuals meeting NF2 criteria who initially presented with a unilateral VS. Of these, 83 (40.7%) went on to develop a contralateral VS. We concentrated our genetic analysis on a group of 70 who initially fulfilled NF2 criteria with a unilateral vestibular schwannoma and at least 2 additional nonintradermal schwannomas.

RESULTS

Overall, 5/70 (7%) individuals with unilateral VS and at least 2 other schwannomas had a pathogenic or likely pathogenic LZTR1 mutation. Twenty of the 70 subsequently developed bilateral disease. Of the remaining 50, 5 (10%) had a germline LZTR1 mutation, equivalent to the number (n = 5) with a germline NF2 mutation.

CONCLUSIONS

The most common etiology for unilateral VS and 2 additional NF2-associated tumors in this cohort was mosaic NF2. Germline LZTR1 and germline NF2 mutations were equally common in our cohort. This indicates that LZTR1 must be considered when making a diagnosis of NF2 in the presence of unilateral VS in individuals without a germline NF2 mutation.

Bilateral vestibular schwannomas in older patients: NF2 or chance?

BACKGROUND

Neurofibromatosis type 2 (NF2) is an autosomal dominant condition with high spontaneous mutation rate which predisposes to the development of multiple nerve sheath tumours (schwannomas), meningiomas and ependymoma. The cardinal feature and main diagnostic criterion for the diagnosis of NF2 remains the development of bilateral vestibular schwannoma (BVS). With increasing use of MRI screening the possibility of a 'chance' diagnosis of BVS has been mooted with a potential frequency of one in two million people in their lifetime. Until now, however, no evidence for such an event has been published. We aimed to demonstrate that chance occurrence can occur and to estimate its frequency among those with just BVS late in life.

METHODS

Two vestibular schwannomas from the same patient were DNA sequenced and underwent loss of heterozygosity analysis.

RESULTS

We show that a man who developed BVS, at ages 52 and 67 years developed these tumours sporadically by demonstrating that there were no molecular events in common between the two tumours. Furthermore from a database of over 1200 patients with NF2, we have estimated that ~25% of cases of BVS over 50 years and 50% over 70 years of age where no other features of NF2 are present represent a chance occurrence rather than due to an underlying mosaic or constitutional NF2 mutation.

CONCLUSIONS

Patients presenting with BVS later in life should be appraised of the potential likelihood they may not have NF2 and the resultant further reduction in risks of transmission to offspring.

Circulating free DNA as a surrogate for tumor material for EGFR and KRAS analysis

The analysis of a patient's tumor mutation status has become increasingly important. Pharmaceuticals such as gefitinib require that a mutation test is performed prior to treatment to help predict a positive outcome to the patient before the drug is administered. However, obtaining a suitable tumor sample for analysis is not always possible and therefore some patients that may benefit will not receive the drug. The use of easily obtainable samples such as plasma or serum would be ideal if tumor derived material could be readily extracted and contained the same predictive mutations as the source tumor.

We have evaluated circulating free (cf) DNA from plasma, and to a lesser extent serum, from lung cancer patients for EGFR and KRAS mutations using allele specific PCR tests (ARMSTM). The majority of the samples had no matched tumor sample available so the mutation detection rate was compared to the expected frequency of mutations in this tumor and population type. EGFR mutations were detected in 21 of 237 plasma cf DNA samples (8.9%) (expected: 10-15%). KRAS mutations were detected in 11 of 168 plasma cf DNA samples (6.6%) (expected: 17%). Where analysis was performed on the matched cf DNA extracted from serum the mutation detection rate was lower than in plasma. Interestingly the EGFR mutation frequency was higher than KRAS in the plasma samples, although the KRAS mutation frequency was expected to be higher than EGFR mutation frequency in the tumors. This could be due to the frequent amplification of mutant EGFR in lung tumors resulting in more target copies in the cf DNA, the EGFR assays could be more sensitive or perhaps the nature of EGFR mutation containing tumors is different making them shed more DNA or survive longer in the blood. In conclusion, cf DNA derived from plasma is a useful surrogate for mutation detection when no tumor sample is available, but the mutation detection rate is not equal for different mutations in different genes.

What are the implications in individuals with unilateral vestibular schwannoma and other neurogenic tumors?

OBJECTIVES

Individuals who develop a unilateral vestibular schwannoma (VS) and other neurogenic tumors are at high risk of having the inherited condition neurofibromatosis Type 2 (NF2). The risk of bilateral disease and transmission risk to offspring are important in surgical planning and counseling. The authors have attempted to resolve these risks.

METHODS

A large NF2 dataset was interrogated for individuals who had initially presented with a unilateral VS and other tumors before developing bilateral disease, to assess the contralateral and offspring risks.

RESULTS

Ninety-six patients with a unilateral VS and additional neurogenic tumors had a bilaterality rate of 48% at 20 years in those initially diagnosed when > 18 years of age and 82% if presenting earlier. Constitutional NF2 mutations were found in blood in 25 (27%) of 92, but 13 (76%) of 17 patients presenting with unilateral VS at < or = 18 years of age. Tumor analysis suggests that the vast majority of the remainder are mosaic for an NF2 mutation.

CONCLUSIONS

Patients with unilateral VS and other NF2-related tumors who fulfill Manchester criteria have a high risk of developing a contralateral tumor, especially if presenting in childhood. Transmission risks are reduced for offspring, particularly in the older patients who are likely to be mosaic.

Mosaicism in neurofibromatosis type 2: an update of risk based on uni/bilaterality of vestibular schwannoma at presentation and sensitive mutation analysis including multiple ligation-dependent probe amplification

BACKGROUND

Neurofibromatosis type 2 (NF2) is almost unique among inherited disorders in the frequency of mosaicism in the first affected generation. However, the implications of this on transmission risks have not been fully elucidated.

METHODS

The expanded database of 460 families with NF2 and 704 affected individuals was analysed for mosaicism and transmission risks to offspring.

RESULTS

64 mosaic patients, with a projected mosaicism rate of 33% for sporadic classical NF2 with bilateral vestibular schwannoma at presentation and 60% for those presenting unilaterally, were identified. Offspring risks can be radically reduced on the basis of a sensitive mutation analysis of blood DNA including multiple ligation-dependent probe amplification (MLPA, which detects 15% of all mutations), but even MLPA cannot detect high levels of mosaicism.

CONCLUSION

The chances of mosaicism in NF2 and the resultant risks of transmission of the mutation to offspring in a number of different clinical situations have been further delineated. The use of MLPA in this large NF2 series is also reported for the first time.

Should NF2 mutation screening be undertaken in patients with an apparently isolated vestibular schwannoma?

Early onset of vestibular schwannoma (VS) is associated with the inherited condition neurofibromatosis type 2 (NF2). However, the majority of NF2 presents bilaterally and the proportion of early-onset apparent sporadic unilateral VS because of NF2 remains to be determined. We have determined the risk by studying NF2 risk in a population-based set of VS, looking at the mode of presentation in a large NF2 data set and the outcome of NF2 mutation analysis in 148 sporadic unilateral VS. The risk of NF2 in an apparently sporadic case of unilateral VS is small apart from in the very youngest age group (<20 years). NF2 germ line mutation testing is unlikely to reveal a mutation except <20 years as a result of the low risk and high rates of mosaicism. Germ line mutation testing is probably only justified in sporadic unilateral VS <20 years unless other features of NF2 are present. Ideally mutation testing should start with the original tumour specimen.