Constitutional mosaicism of a de novo TP53 mutation in a patient with bilateral choroid plexus carcinoma

Tumors of Choroid Plexus and Other Ventricular Tumors

Tumors arising inside the ventricular system are rare but represent a difficult diagnostic and therapeutic challenge. They usually are diagnosed when reaching a big volume and tend to affect young children. There is a wide broad of differential diagnoses with significant variability in anatomical aspects and tumor type. Differential diagnosis in tumor type includes choroid plexus tumors (papillomas and carcinomas), ependymomas, subependymomas, subependymal giant cell astrocytomas (SEGAs), central neurocytomas, meningiomas, and metastases. Choroid plexus tumors, ependymomas of the posterior fossa, and SEGAs are more likely to appear in childhood, whereas subependymomas, central neurocytomas, intraventricular meningiomas, and metastases are more frequent in adults. This chapter is predominantly focused on choroid plexus tumors and radiological and histological differential diagnosis. Treatment is discussed in the light of the modern acquisition in genetics and epigenetics of brain tumors.

Systematic detection of mosaicism by using digital NGS reveals three new MEN1 mosaicisms

Purpose

Mosaicism is a feature of several inherited tumor syndromes. Only a few cases of mosaicism have been described in multiple endocrine neoplasia type 1 (MEN1). Next-generation sequencing (NGS) offers new possibilities for detecting mosaicism. Here, we report the first study to systematically look for MEN1 mosaicism, using blood DNA, in MEN1-suspected patients but without MEN1 pathogenic variants (PV) in a heterozygous state.

Methods

Digital targeted NGS, including unique molecular identifiers (UMIs), was performed in routine practice, and the analytic performance of this method was verified.

Results

Among a cohort of 119 patients harboring from 2 to 5 MEN1 lesions, we identified 3 patients with MEN1 mosaic PVs. The allele frequencies ranged from 2.3 to 9.5%. The detection rate of MEN1 mosaicism in patients bearing at least 3 MEN1 lesions was 17% (3/18). No cases were detected in patients with two lesions.

Conclusion

We report here three new cases with MEN1 mosaicism. This study examined the performance of UMI in the diagnosis of MEN1 mosaicism in routine practice, and our results underline that the frequency of mosaicism is probably underestimated in patients with suspected MEN1.

Sensorineural hearing loss in GSD type I patients. A newly recognized symptomatic association of potential clinical significance and unclear pathomechanism

OBJECTIVE

Glycogen storage disease (GSD) type I is an inborn error of carbohydrates metabolism characterized by inability to convert glucose-6-phosphate to glucose. It presents with serious liver and metabolic complications, as well as in type Ib with severe infections due to neutropenia. So far, the sensorineural hearing impairment has not been reported in these patients. Bilateral, sensorineural hearing impairment was diagnosed in four unrelated GSDI patients. Congenital origin of hearing loss and descending audiometric curves warranted the need for future investigations.

METHODS

Hearing status was assessed in entire group of 40 children with GSD type I. Then, molecular testing, massive parallel sequencing was performed in the four probands and their parents in order to find possible genetic background of auditory dysfunction in these patients.

RESULTS

Pathogenic variants in G6PC and SLC37A4 related to the phenotypes of GSDI subtype Ia and subtype Ib were detected, each in two probands, respectively. No change in the genes involved in auditory pathway dysfunction was found.

CONCLUSIONS

Sensorineural hearing loss appears to be associated with GSDI in approximately one out of ten cases. Careful assessment and monitoring of auditory functions of patients with GSDI is recommended.

Cancer predisposition in pediatric neuro-oncology-practical approaches and ethical considerations

A genetic predisposition to tumor development can be identified in up to 10% of pediatric patients with central nervous system (CNS) tumors. For some entities, the rate of an underlying predisposition is even considerably higher. In recent years, population-based approaches have helped to further delineate the role of cancer predisposition in pediatric oncology. Investigations for cancer predisposition syndrome (CPS) can be guided by clinical signs and family history leading to directed testing of specific genes. The increasingly adopted molecular analysis of tumor and often parallel blood samples with multi-gene panel, whole-exome, or whole-genome sequencing identifies additional patients with or without clinical signs. Diagnosis of a genetic predisposition may put an additional burden on affected families. However, information on a given cancer predisposition may be critical for the patient as potentially influences treatment decisions and may offer the patient and healthy carriers the chance to take part in intensified surveillance programs aiming at early tumor detection. In this review, we discuss some of the practical and ethical challenges resulting from the widespread use of new diagnostic techniques and the most important CPS that may manifest with brain tumors in childhood.

Pre- and Post-Zygotic TP53 De Novo Mutations in SHH-Medulloblastoma

Simple Summary

Medulloblastoma is the most common malignant brain tumor in children. In a subset of cases, a causal factor is a constitutive mutation of the TP53 gene, which may be inherited or arise for the first time in a patient (de novo). Using an immunohistochemistry assay as a screening tool, we selected patients suspected of harboring a TP53 mutation and offered genetic counseling and germline testing. Our study, which was the first to investigate the parental origin of TP53 mutations in medulloblastoma, allowed the identification of two additional cases with de novo mutations. Moreover, we demonstrated that in one patient the mutation originated at a post-zygotic stage, resulting in somatic mosaicism. These findings have important implications for genetic counseling since they highlight the occurrence of both pre- and post-zygotic TP53 de novo mutations in medulloblastoma, pointing out that in a specific subgroup of patients genetic testing should be offered regardless of family history.

Abstract

Li-Fraumeni syndrome (LFS) is an autosomal dominant disorder caused by mutations in the TP53 gene, predisposing to a wide spectrum of early-onset cancers, including brain tumors. In medulloblastoma patients, the role of TP53 has been extensively investigated, though the prevalence of de novo mutations has not been addressed. We characterized TP53 mutations in a monocentric cohort of consecutive Sonic Hedgehog (SHH)-activated medulloblastoma patients. Germline testing was offered based on tumor p53 immunostaining positivity. Among 24 patients, three (12.5%) showed tumor p53 overexpression, of whom two consented to undergo germline testing and resulted as carriers of TP53 mutations. In the first case, family history was uneventful and the mutation was not found in either of the parents. The second patient, with a family history suggestive of LFS, unexpectedly resulted as a carrier of the mosaic mutation c.742=/C>T p.(Arg248=/Trp). The allele frequency was 26% in normal tissues and 42–77% in tumor specimens. Loss of heterozygosity (LOH) in the tumor was also confirmed. Notably, the mosaic case has been in complete remission for more than one year, while the first patient, as most TP53-mutated medulloblastoma cases from other cohorts, showed a severe and rapidly progressive disease. Our study reported the first TP53 mosaic mutation in medulloblastoma patients and confirmed the importance of germline testing in p53 overexpressed SHH-medulloblastoma, regardless of family history.

Epigenetics impacts upon prognosis and clinical management of choroid plexus tumors

PURPOSE

Choroid plexus tumors comprise of choroid plexus papilloma (CPP, WHO grade I), atypical choroid plexus papilloma (aCPP, WHO grade II) and choroid plexus carcinoma (CPC, WHO grade III). Molecular events driving the majority of choroid plexus tumors remain poorly understood. Recently, DNA methylation profiling has revealed different epigenetic subgroups.

METHODS

Comprehensive review of epigenetic profiles of choroid plexus tumors in the context of histopathological, genetic, and clinical features. DNA methylation profiling segregates choroid plexus tumors into three distinct epigenetic subgroups: supratentorial pediatric low-risk choroid plexus tumors (CPP and aCPP), infratentorial adult low-risk choroid plexus tumors (CPP and aCPP), and supratentorial pediatric high-risk choroid plexus tumors (CPP and aCPP and CPC). Epigenetic subgrouping provides additional prognostic information in comparison to histopathological grading.

CONCLUSIONS

Epigenetic profiling of choroid plexus tumors can be used for the identification of patients at risk of recurrence and is expected to play a role for treatment stratification and patient management in the context of future clinical trials.

Mosaic PTEN alteration in the neural crest during embryogenesis results in multiple nervous system hamartomas

The contribution of mosaic alterations to tumors of the nervous system and to non-malignant neurological diseases has been unmasked thanks to the development of Next Generation Sequencing (NGS) technologies. We report here the case of a young patient without any remarkable familial medical history who was first referred at 7 years of age, for an autism spectrum disorder (ASD) of Asperger type, not associated with macrocephaly. The patient subsequently presented at 10 years of age with multiple nodular lesions located within the trigeminal, facial and acoustic nerve ganglia and at the L3 level. Histological examination of this latter lesion revealed a glioneuronal hamartoma, exhibiting heterogeneous PTEN immunoreactivity, astrocyte and endothelial cell nuclei expressing PTEN, but not ganglion cells. NGS performed on the hamartoma allowed the detection of a PTEN pathogenic variant in 30% of the reads. The presence of this variant in the DNA extracted from blood and buccal swabs in 3.5 and 11% of the NGS reads, respectively, confirmed the mosaic state of the PTEN variant. The anatomical distribution of the lesions suggests that the mutational event affecting PTEN occurred in neural crest progenitors, thus explaining the absence of macrocephaly. This report shows that mosaic alteration of PTEN may result in multiple central and peripheral nervous system hamartomas and that the presence of such alteration should be considered in patients with multiple nervous system masses, even in the absence of cardinal features of PTEN hamartoma tumor syndrome, especially macrocephaly.

Immunohistochemical detection of ALK protein identifies APC mutated medulloblastoma and differentiates the WNT-activated medulloblastoma from other types of posterior fossa childhood tumors

Expression of the ALK gene strongly correlates with the WNT-activated medulloblastomas, which are routinely identified by detection of CTNNB1 mutation. However, some tumors have mutations in other than CTNNB1 genes. Therefore, we investigated if ALK expression may identify WNT-activated tumors without CTNNB1 mutation. In addition, we examined if ALK expression may differentiate WNT-activated medulloblastoma from other malignant posterior fossa tumors. ALK expression was analyzed using immunohistochemistry (clone D5F3) in 70 patients with posterior fossa tumours. Among 55 medulloblastomas, 6 tumors showed ALK expression in > 50% of tumor cells. In one tumor, with ALK positive reaction, negative nuclear reaction against β-catenin and the lack of CTNNB1 mutation, next generation sequencing revealed a presence of pathogenic variant c.3366_3369del in the APC gene, with homozygous deletion leading to inactivation of both copies in tumor cells. MLPA analysis displayed the presence of chromosome 6 monosomy, therefore, confirming the WNT type of this tumor. All analyzed 19 anaplastic ependymomas, 4 choroid plexus carcinomas and 2 atypical teratoid rhabdoid tumors were immunonegative for ALK expression. Therefore, we propose, that immunohistochemical detection of ALK protein should be highly recommended in routine investigation, in parallel to already established methods for identification and differentiation of WNT-activated medulloblastoma.