Medulloblastoma, macrocephaly, and a pathogenic germline PTEN variant: Cause or coincidence?

Case report: A case study of variant calling pipeline selection effect on the molecular diagnostics outcome

Next-generation sequencing technologies have not only defined a breakthrough in medical genetics, but also been able to enter routine clinical practice to determine individual genetic susceptibilities. Modern technological developments are routinely introduced to genetic analysis overtaking the established approaches, potentially raising a number of challenges. To what extent is the advantage of new methodologies in synthetic metrics, such as precision and recall, more important than stability and reproducibility? Could differences in the technical protocol for calling variants be crucial to the diagnosis and, by extension, the patient's treatment strategy? A regulatory review process may delay the incorporation of potentially beneficial technologies, resulting in missed opportunities to make the right medical decisions. On the other hand, a blind adoption of new technologies based solely on synthetic metrics of precision and recall can lead to incorrect conclusions and adverse outcomes for the specific patient. Here, we use the example of a patient with a WHO-diagnosed desmoplastic/nodular SHH-medulloblastoma to explore how the choice of DNA variant search protocol affects the genetic diagnostics outcome.

Cerebellar phenotypes in germline PTEN mutation carriers

PTEN hamartoma tumour syndrome (PHTS) comprises different hereditary conditions caused by germline PTEN mutations, predisposing to the development of multiple hamartomas in many body tissues and also increasing the risk of some types of cancer. Cerebellar involvement in PHTS patients has been long known due to the development of a pathognomonic cerebellar hamartoma (known as dysplastic gangliocytoma of the cerebellum or Lhermitte-Duclos disease). Recently, a crucial role of the cerebellum has been highlighted in the pathogenesis of autism spectrum disorders, now recognised as a phenotype expressed in a variable percentage of PHTS children. In addition, rare PTEN variants are indeed identified in medulloblastoma as well, even if they are less frequent than other germline gene mutations. The importance of PTEN and its downstream signalling enzymatic pathways, PI3K/AKT/mTOR, has been studied at different levels in both human clinical settings and animal models, not only leading to a better understanding of the pathogenesis of different disorders but, most importantly, to identify potential targets for specific therapies. In particular, PTEN integrity makes an important contribution to the normal development of tissue architecture in the nervous system, including the cerebellum. Thus, in patients with PTEN germline mutations, the cerebellum is an affected organ that is increasingly recognised in different disorders, whereas, in animal models, cerebellar Pten loss causes a variety of functional and histological alterations. In this review, we summarise the range of cerebellar involvement observed in PHTS and its relationships with germline PTEN mutations, along with the phenotypes expressed by murine models with PTEN deficiency in cerebellar tissue.

SHH medulloblastoma and very early onset of bowel polyps in a child with PTEN hamartoma tumor syndrome

Phosphatase and tensin homolog (PTEN) hamartoma tumor syndrome (PHTS) is a cancer predisposition syndrome characterized by an increased risk of developing benign and malignant tumors, caused by germline pathogenic variants of the PTEN tumour suppressor gene. PTEN gene variants often present in childhood with macrocephaly, developmental delay, and/or autism spectrum disorder while tumors and intestinal polyps are commonly detected in adults. PHTS is rarely associated with childhood brain tumors with only two reported cases of medulloblastoma (MB). We report the exceptional case of an infant carrying a germline and somatic pathogenic variant of PTEN and a germline and somatic pathogenic variant of CHEK2 who developed a MB SHH in addition to intestinal polyposis.

Medulloblastoma and Cowden syndrome: Further evidence of an association

Cowden syndrome (CS) is an autosomal dominant hamartoma and tumor predisposition syndrome caused by heterozygous pathogenic germline variants in PTEN in most affected individuals. Major features include macrocrania, multiple facial tricholemmomas, acral and oral keratoses and papillomas, as well as mammary, non-medullary thyroid, renal, and endometrial carcinomas. Lhermitte-Duclos disease (LDD), or dysplastic gangliocytoma of the cerebellum, is the typical brain tumor associated with CS; the lifetime risk for LDD in CS patients has been estimated to be as high as 30%. In contrast, medulloblastoma is much rarer in CS, with only 4 reported cases in the literature. We report a 5th such patient. All 5 patients were diagnosed between 1 and 2 years of age and not all showed the pathognomonic clinical stigmata of CS at the time of their medulloblastoma diagnosis. Where detailed information was available, the medulloblastoma was of the SHH-subtype, in keeping with the observation that in sporadic medulloblastomas, PTEN-alterations are usually encountered in the SHH-subtype. Medulloblastomas can be associated with several tumor-predisposition syndromes and of the 4 medulloblastoma subtypes, SHH-medulloblastomas in children have the highest prevalence of predisposing germline variants (approx. 40%). CS should be added to the list of SHH-medulloblastoma-associated syndromes. Germline analysis of PTEN should be performed in infants with SHH-medulloblastomas, regardless of their clinical phenotype, especially if they do not carry pathogenic germline variants in PTEN or PTEN, the most commonly altered predisposing genes in this age-group. In addition, these cases show that CS has a biphasic brain tumor distribution, both in regards to the age of onset and the tumor type: a small number of CS patients develop a medulloblastoma in infancy while many more develop LDD in adulthood.

The Role of MicroRNAs in Therapeutic Resistance of Malignant Primary Brain Tumors

Brain tumors in children and adults are challenging tumors to treat. Malignant primary brain tumors (MPBTs) such as glioblastoma have very poor outcomes, emphasizing the need to better understand their pathogenesis. Developing novel strategies to slow down or even stop the growth of brain tumors remains one of the major clinical challenges. Modern treatment strategies for MPBTs are based on open surgery, chemotherapy, and radiation therapy. However, none of these treatments, alone or in combination, are considered effective in controlling tumor progression. MicroRNAs (miRNAs) are 18-22 nucleotide long endogenous non-coding RNAs that regulate gene expression at the post-transcriptional level by interacting with 3'-untranslated regions (3'-UTR) of mRNA-targets. It has been proven that miRNAs play a significant role in various biological processes, including the cell cycle, apoptosis, proliferation, differentiation, etc. Over the last decade, there has been an emergence of a large number of studies devoted to the role of miRNAs in the oncogenesis of brain tumors and the development of resistance to radio- and chemotherapy. Wherein, among the variety of molecules secreted by tumor cells into the external environment, extracellular vesicles (EVs) (exosomes and microvesicles) play a special role. Various elements were found in the EVs, including miRNAs, which can be transported as part of these EVs both between neighboring cells and between remotely located cells of different tissues using biological fluids. Some of these miRNAs in EVs can contribute to the development of resistance to radio- and chemotherapy in MPBTs, including multidrug resistance (MDR). This comprehensive review examines the role of miRNAs in the resistance of MPBTs (e.g., high-grade meningiomas, medulloblastoma (MB), pituitary adenomas (PAs) with aggressive behavior, and glioblastoma) to chemoradiotherapy and pharmacological treatment. It is believed that miRNAs are future therapeutic targets in MPBTs and such the role of miRNAs needs to be critically evaluated to focus on solving the problems of resistance to therapy this kind of human tumors.

Medulloblastoma, macrocephaly, and a pathogenic germline PTEN variant: Cause or coincidence?

Background

Medulloblastomas (MBs) are a heterogeneous group of childhood brain tumors with four consensus subgroups, namely MB_SHH, MB_WNT, MB_{Group 3}, and MB_{Group 4}, representing the second most common type of pediatric brain cancer after high‐grade gliomas. They suffer from a high prevalence of genetic predisposition with up to 20% of MB_SHH caused by germline mutations in only six genes. However, the spectrum of germline mutations in MB_SHH remains incomplete.

Methods

Comprehensive Next‐Generation Sequencing panels of both tumor and patient blood samples were performed as molecular genetic characterization. The panels cover genes that are known to predispose to cancer.

Results

Here, we report on a patient with a pathogenic germline PTEN variant resulting in an early stop codon p.(Glu7Argfs*4) (ClinVar ID: 480383). The patient developed macrocephaly and MB_SHH, but reached remission with current treatment protocols.

Conclusions

We propose that pathogenic PTEN variants may predispose to medulloblastoma, and show that remission was reached with current treatment protocols. The PTEN gene should be included in the genetic testing provided to patients who develop medulloblastoma at an early age. We recommend brain magnetic resonance imaging upon an unexpected acceleration of growth of head circumference for pediatric patients harboring pathogenic germline PTEN variants.