Beckwith-Wiedemann syndrome: Clinical, histopathological and molecular study of two Tunisian patients and review of literature.

BACKGROUND: Beckwith-Wiedemann syndrome (BWS) is a rare overgrowth syndrome characterized by congenital malformations and predisposition to embryonic tumors. Loss of methylation of imprinting center 2 (IC2) is the most frequent alteration and rarely associated with tumors compared to paternal uniparental disomy of chromosome 11 (UPD(11)pat) and gain of methylation of imprinting center 1. METHODS: Our study aimed to describe the clinical, histopathological and genetic characteristics of two patients and establish genotype-phenotype correlations. The clinical diagnosis was based on the criteria defined by the international expert consensus of BWS. Molecular study of 11p15.5 methylation status was assessed using methylation-specific-multiplex ligation probe amplification (MS-MLPA). RESULTS: Patients were aged 12 months and 3 months and fulfilled the clinical score of BWS. MS-MLPA showed molecular alterations consisting of loss of methylation in IC2 (IC2-LOM) at the maternal allele for one patient and a mosaic UPD(11)pat for the second patient in whom follow-up at 6months revealed adrenocortical carcinoma (ACC) with low grade of malignancy. Molecular subtypes guide the follow-up and tumor surveillance, our major concern. CONCLUSION: We have to take into account the psychological impact of a possible tumor whatever the underlying mechanism is. Nevertheless, the tumor risk remains high for UPD(11)pat. Our study extended the phenotype of BWS with absence of macrosomia in Tunisian patients, contrasting with literature, and added a supplementary case of ACC in the tumor spectrum of BWS patients with UPD(11)pat.

Transient neonatal diabetes mellitus and hypomethylation at additional imprinted loci: novel ZFP57 mutation and review on the literature.

AIM: 6q24-related transient neonatal diabetes mellitus (6q24-TNDM) is a rare imprinting disorder characterized by uncontrolled hyperglycemia during the first 6 months of life. The molecular etiology of 6q24-TNDM is attributable to overexpression of the paternally inherited PLAGL1 and HYMAI genes located on the 6q24 locus. One of these major defects is maternal loss of methylation (LOM) at 6q24. In addition, approximately 50% of TNDM patients that present LOM at 6q24 can also display hypomethylation at additional imprinted loci (multilocus imprinting disturbances, MLID). Interestingly, the majority of these patients carry mutations in the ZFP57 gene, a transcription factor required for the adequate maintenance of methylation during early embryonic development. METHODS: Methylation analysis of 6q24 and additional imprinted loci was carried out by MS-MLPA in a Tunisian male patient with clinical diagnosis of TNMD. For the same patient, mutation analysis of the ZFP57 gene was conducted by direct Sanger sequencing. RESULTS: We report a novel nonsense mutation (c.373C > T; p.R125*; ENST00000376883.1) at the ZFP57 gene causing TNDM-MLID and describe detailed phenotype/epigenotype analysis of TNMD patients carrying ZFP57 mutations. CONCLUSION: We provide additional support to the role of ZFP57 as a genetic determinant cause of MLID in patients with TNMD.

Functional diversity and cooperativity between subclonal populations of pediatric glioblastoma and diffuse intrinsic pontine glioma cells.

The failure to develop effective therapies for pediatric glioblastoma (pGBM) and diffuse intrinsic pontine glioma (DIPG) is in part due to their intrinsic heterogeneity. We aimed to quantitatively assess the extent to which this was present in these tumors through subclonal genomic analyses and to determine whether distinct tumor subpopulations may interact to promote tumorigenesis by generating subclonal patient-derived models in vitro and in vivo. Analysis of 142 sequenced tumors revealed multiple tumor subclones, spatially and temporally coexisting in a stable manner as observed by multiple sampling strategies. We isolated genotypically and phenotypically distinct subpopulations that we propose cooperate to enhance tumorigenicity and resistance to therapy. Inactivating mutations in the H4K20 histone methyltransferase KMT5B (SUV420H1), present in <1% of cells, abrogate DNA repair and confer increased invasion and migration on neighboring cells, in vitro and in vivo, through chemokine signaling and modulation of integrins. These data indicate that even rare tumor subpopulations may exert profound effects on tumorigenesis as a whole and may represent a new avenue for therapeutic development. Unraveling the mechanisms of subclonal diversity and communication in pGBM and DIPG will be an important step toward overcoming barriers to effective treatments.

Genetic study of non-syndromic tooth agenesis through the screening of paired box 9, msh homeobox 1, axin 2, and Wnt family member 10A genes: a case-series.

Non-syndromic tooth agenesis (NSTA) is the most common developmental anomaly in humans. Several studies have been conducted on dental agenesis and numerous genes have been identified. However, the pathogenic mechanisms responsible for NSTA are not clearly understood. We studied a group of 28 patients with sporadic NSTA and nine patients with a family history of tooth agenesis. We focused on four genes - paired box 9 (PAX9), Wnt family member 10A (WNT10A), msh homeobox 1 (MSX1), and axin 2 (AXIN2) - using direct Sanger sequencing of the exons and intron-exon boundaries. The most prevalent variants identified in PAX9 and AXIN2 genes were analyzed using the chi-square test. The sequencing results revealed a number of variants in the AXIN2 gene, including one novel missense mutation in one patient with agenesis of a single second premolar. We also identified one variant in the AXIN2 gene as being a putative risk factor for tooth agenesis. Only one missense mutation was identified in the WNT10A gene and this mutation was found in two patients. Interestingly, WNT10A is reported as the most prevalent gene mutated in the European population with NSTA.

ENPP1 Mutation Causes Recessive Cole Disease by Altering Melanogenesis.

Cole disease is a genodermatosis of pigmentation following a strict dominant mode of inheritance. In this study, we investigated eight patients affected with an overlapping genodermatosis after recessive inheritance. The patients presented with hypo- and hyperpigmented macules over the body, resembling dyschromatosis universalis hereditaria in addition to punctuate palmoplantar keratosis. By homozygosity mapping and whole-exome sequencing, a biallelic p.Cys120Arg mutation in ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) was identified in all patients. We found that this mutation, like those causing dominant Cole disease, impairs homodimerization of the ENPP1 enzyme that is mediated by its two somatomedin-B-like domains. Histological analysis revealed structural and molecular changes in affected skin that were likely to originate from defective melanocytes because keratinocytes do not express ENPP1. Consistently, RNA-sequencing analysis of patient-derived primary melanocytes revealed alterations in melanocyte development and in pigmentation signaling pathways. We therefore conclude that germline ENPP1 cysteine-specific mutations, primarily affecting the melanocyte lineage, cause a clinical spectrum of dyschromatosis, in which the p.Cys120Arg allele represents a recessive and more severe form of Cole disease.

Molecular Diagnostic and Prognostic Subtyping of Gliomas in Tunisian Population.

It has become increasingly evident that morphologically similar gliomas may have distinct clinical phenotypes arising from diverse genetic signatures. To date, glial tumours from the Tunisian population have not been investigated. To address this, we correlated the clinico-pathology with molecular data of 110 gliomas by a combination of HM450K array, MLPA and TMA-IHC. PTEN loss and EGFR amplification were distributed in different glioma histological groups. However, 1p19q co-deletion and KIAA1549:BRAF fusion were, respectively, restricted to Oligodendroglioma and Pilocytic Astrocytoma. CDKN2A loss and EGFR overexpression were more common within high-grade gliomas. Furthermore, survival statistical correlations led us to identify Glioblastoma (GB) prognosis subtypes. In fact, significant lower overall survival (OS) was detected within GB that overexpressed EGFR and Cox2. In addition, IDH1R132H mutation seemed to provide a markedly survival advantage. Interestingly, the association of IDHR132H mutation and EGFR normal status, as well as the association of differentiation markers, defined GB subtypes with good prognosis. By contrast, poor survival GB subtypes were defined by the combination of PTEN loss with PDGFRa expression and/or EGFR amplification. Additionally, GB presenting p53-negative staining associated with CDKN2A loss or p21 positivity represented a subtype with short survival. Thus, distinct molecular subtypes with individualised prognosis were identified. Interestingly, we found a unique histone mutation in a poor survival young adult GB case. This tumour exceptionally associated the H3F3A G34R mutation and MYCN amplification as well as 1p36 loss and 10q loss. Furthermore, by exhibiting a remarkable methylation profile, it emphasised the oncogenic power of G34R mutation connecting gliomagenesis and chromatin regulation.

Characterization of a novel mutation in PAX9 gene in a family with non-syndromic dental agenesis.

BACKGROUND: Dental agenesis is the most common developmental anomaly in man and may present either as an isolated trait or as part of a syndrome, such as ectodermal dysplasia. Until now, the underlying molecular pathogenic mechanisms responsible for dental agenesis are still largely unknown. Several genetic and molecular studies have demonstrated that at least 300 genes are involved in tooth formation and development, coding for specific transcriptional factors, receptors or growth factors that are expressed at specific developmental stages. Dental agenesis in this respect is believed to result from altered expression of one or more of these factors during initiation and early morphogenesis of the tooth germ, and the first actors identified were MSX1 and PAX9. DESIGN: In this study, we focalized on a Tunisian family with a non-syndromic autosomal dominant form of tooth agenesis. In order to screen for the eventual genetic cause of dental agenesis in this family we sequenced 4 genes; PAX9, WNT10A, MSX1 and AXIN2 using Sanger sequencing. RESULTS: Direct Screening analysis of PAX9 gene, revealed a novel mutation p.Asp200Serfs*13. It consists of a duplication of 5 basepairs leading to a codon stop 13 position downstream. This novel mutation was found in all affected family members. CONCLUSIONS: In this report, we present the first genetic study of a Tunisian family with a non-syndromic autosomal dominant form of tooth agenesis, in which we identified in PAX9 gene a novel mutation. It most likely results in nonsense mediated RNA decay and haploinsifficiency that reduce the transactivation capacity of PAX9.

Partial KCNQ1OT1 hypomethylation: A disguised familial Beckwith-Wiedemann syndrome as a sporadic adrenocortical tumor.

Beckwith-Wiedemann syndrome has a wide spectrum of complications such as embryonal tumors, namely adrenocortical tumor. Tumor predisposition is one of the most challenging manifestations of this syndrome. A 45-day old female with a family history of adrenocortical tumor presented with adrenocortical tumor. The case raised suspicion of a hereditary Beckwith-Wiedemann syndrome, therefore molecular analysis was undertaken. The results revealed partial KCNQ1OT1 hypomethylation in the infant's blood DNA which was associated with a complete loss of methylation in the infant's adrenocortical tumor tissue. It is unique for familial Beckwith-Wiedemann syndrome caused by KCNQ1OT1 partial hypomethylation to manifest solely through adrenocortical tumor. Incomplete penetrance and specific tissue mosaicism could provide explanations to this novel hereditary Beckwith-Wiedemann syndrome presentation.

Assessment of MYCN amplification status in Tunisian neuroblastoma: CISH and MLPA combining approach.

BACKGROUND: Neuroblastoma (NB) shows a complex combination of genetic aberrations. Some of them represent poor genetic prognosis factors that require specific and intensive chemotherapy. MYCN amplification consists of the major bad outcome prognostic factor, it is indeed frequently observed in aggressive neuroblastomas. To date different methods are used for MYCN status detection. OBJECTIVES: The primary aim of our study was to provide a critical assessment of MYCN status using 2 molecular techniques CISH and MLPA. We also focused on the correlation between neuroblastoma genetic markers and patient's clinical course among 15 Tunisian patients. METHODS: we developed a descriptive study that includes 15 pediatric Tunisian patients referred to our laboratory from 2004 to 2011. We reported the analysis of fresh and FFPE NB tumors tissues. RESULTS: No significant correlation was found between COG grade and patients overall survival. Assessment of NMYC gene copy number by kappa statistic test revealed high concordance between CISH and MLPA tests (kappa coefficient = 0.02). CONCLUSION: Despite misdiagnosing of MYCN status fewer than 5 copies, MLPA remains an effective molecular technique that enables a large panel of genomic aberrations screening. Thus combining CISH and MLPA is an effective molecular approach adopted in our laboratory. Our results allow pediatric oncologists to set up the first Neuroblastoma therapeutic strategy based on molecular markers in Tunisia.

Rundataxin, a novel protein with RUN and diacylglycerol binding domains, is mutant in a new recessive ataxia.

We have identified a novel form of recessive ataxia that segregates in three children of a large consanguineous Saudi Arabian family. The three patients presented with childhood onset gait and limb ataxia, dysarthria and had limited walking without aid into their teenage years. Two patients developed epilepsy at 7 months without relapse after treatment, and mental retardation. Linkage studies allowed us to identify a single locus that segregated with the disease on chromosome 3q28-qter. Mutation screening of all coding sequences revealed a single nucleotide deletion, 2927delC, in exon 19 of the KIAA0226 gene, which results in a frame shift of the C-terminal domain (p.Ala943ValfsX146). The KIAA0226 gene encodes a protein that we named rundataxin, with two conserved domains: an N-terminal RUN domain and a C-terminal domain containing a diacylglycerol binding-like motif. The closest paralogue of rundataxin, the plekstrin homology domain family member M1, has been shown to colocalize with Rab7, a small GTPase associated with late endosomes/lysosomes, suggesting that rundataxin may also be associated with vesicular trafficking and signalling pathways through its RUN and diacylglycerol binding-like domains. The rundataxin pathway appears therefore distinct from the ataxia pathways involving deficiency in mitochondrial or nuclear proteins and broadens the range of mechanisms leading to recessive ataxias.

Mutations in ABHD12 cause the neurodegenerative disease PHARC: An inborn error of endocannabinoid metabolism.

Polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataract (PHARC) is a neurodegenerative disease marked by early-onset cataract and hearing loss, retinitis pigmentosa, and involvement of both the central and peripheral nervous systems, including demyelinating sensorimotor polyneuropathy and cerebellar ataxia. Previously, we mapped this Refsum-like disorder to a 16 Mb region on chromosome 20. Here we report that mutations in the ABHD12 gene cause PHARC disease and we describe the clinical manifestations in a total of 19 patients from four different countries. The ABHD12 enzyme was recently shown to hydrolyze 2-arachidonoyl glycerol (2-AG), the main endocannabinoid lipid transmitter that acts on cannabinoid receptors CB1 and CB2. Our data therefore represent an example of an inherited disorder related to endocannabinoid metabolism. The endocannabinoid system is involved in a wide range of physiological processes including neurotransmission, mood, appetite, pain appreciation, addiction behavior, and inflammation, and several potential drugs targeting these pathways are in development for clinical applications. Our findings show that ABHD12 performs essential functions in both the central and peripheral nervous systems and the eye. Any future drug-mediated interference with this enzyme should consider the potential risk of long-term adverse effects.