Biallelic loss-of-function variants of ZFTRAF1 cause neurodevelopmental disorder with microcephaly and hypotonia.

PURPOSE: Neurodevelopmental disorders exhibit clinical and genetic heterogeneity, ergo manifest dysfunction in components of diverse cellular pathways; the precise pathomechanism for the majority remains elusive. METHODS: We studied five affected individuals from three unrelated families manifesting global developmental delay, postnatal microcephaly, and hypotonia. We employed exome sequencing and prioritized variants that were subsequently characterized using immunofluorescence, immunoblotting, pulldown assays, and RNA sequencing. RESULTS: We identified biallelic variants in ZFTRAF1, encoding a protein of yet unknown function. Four affected individuals from two unrelated families segregated two homozygous frameshift variants in ZFTRAF1, whereas, in the third family, an intronic splice site variant was detected. We investigated ZFTRAF1 at the cellular level and signified it as a nucleocytoplasmic protein in different human cell lines. ZFTRAF1 was completely absent in the fibroblasts of two affected individuals. We also identified 110 interacting proteins enriched in mRNA processing and autophagy-related pathways. Based on profiling of autophagy markers, patient-derived fibroblasts show irregularities in the protein degradation process. CONCLUSION: Thus, our findings suggest that biallelic variants of ZFTRAF1 cause a severe neurodevelopmental disorder.

A Homozygous NDUFS6 Variant Associated with Neuropathy and Optic Atrophy.

Background: The NADH dehydrogenase [ubiquinone] iron-sulfur protein 6 (NDUFS6) gene encodes for an accessory subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (complex I). Bi-allelic NDUFS6 variants have been linked with a severe disorder mostly reported as a lethal infantile mitochondrial disease (LMID) or Leigh syndrome (LS). Objective: Here, we identified a homozygous variant (c.309 + 5 G > A) in NDUFS6 in one male patient with axonal neuropathy accompanied by loss of small fibers in skin biopsy and further complicated by optic atrophy and borderline intellectual disability. Methods: To address the pathogenicity of the variant, biochemical studies (mtDNA copy number quantification, ELISA, Proteomic profiling) of patient-derived leukocytes were performed. Results: The analyses revealed loss of NDUFS6 protein associated with a decrease of three further mitochondrial NADH dehydrogenase subunit/assembly proteins (NDUFA12, NDUFS4 and NDUFV1). Mitochondrial copy number is not altered in leukocytes and the mitochondrial biomarker GDF15 is not significantly changed in serum. Conclusions: Hence, our combined clinical and biochemical data strengthen the concept of NDUFS6 being causative for a very rare form of axonal neuropathy associated with optic atrophy and borderline intellectual disability, and thus expand (i) the molecular genetic landscape of neuropathies and (ii) the clinical spectrum of NDUFS6-associated phenotypes.

Delineation of the adult phenotype of Coffin-Siris syndrome in 35 individuals.

Coffin-Siris syndrome (CSS) is a rare multisystemic autosomal dominant disorder. Since 2012, alterations in genes of the SWI/SNF complex were identified as the molecular basis of CSS, studying largely pediatric cohorts. Therefore, there is a lack of information on the phenotype in adulthood, particularly on the clinical outcome in adulthood and associated risks. In an international collaborative effort, data from 35 individuals ≥ 18 years with a molecularly ascertained CSS diagnosis (variants in ARID1B, ARID2, SMARCA4, SMARCB1, SMARCC2, SMARCE1, SOX11, BICRA) using a comprehensive questionnaire was collected. Our results indicate that overweight and obesity are frequent in adults with CSS. Visual impairment, scoliosis, and behavioral anomalies are more prevalent than in published pediatric or mixed cohorts. Cognitive outcomes range from profound intellectual disability (ID) to low normal IQ, with most individuals having moderate ID. The present study describes the first exclusively adult cohort of CSS individuals. We were able to delineate some features of CSS that develop over time and have therefore been underrepresented in previously reported largely pediatric cohorts, and provide recommendations for follow-up.

EphrinA5 regulates cell motility by modulating Snhg15/DNA triplex-dependent targeting of DNMT1 to the Ncam1 promoter.

Cell-cell communication is mediated by membrane receptors and their ligands, such as the Eph/ephrin system, orchestrating cell migration during development and in diverse cancer types. Epigenetic mechanisms are key for integrating external "signals", e.g., from neighboring cells, into the transcriptome in health and disease. Previously, we reported ephrinA5 to trigger transcriptional changes of lncRNAs and protein-coding genes in cerebellar granule cells, a cell model for medulloblastoma. LncRNAs represent important adaptors for epigenetic writers through which they regulate gene expression. Here, we investigate a lncRNA-mediated targeting of DNMT1 to specific gene loci by the combined power of in silico modeling of RNA/DNA interactions and wet lab approaches, in the context of the clinically relevant use case of ephrinA5-dependent regulation of cellular motility of cerebellar granule cells. We provide evidence that Snhg15, a cancer-related lncRNA, recruits DNMT1 to the Ncam1 promoter through RNA/DNA triplex structure formation and the interaction with DNMT1. This mediates DNA methylation-dependent silencing of Ncam1, being abolished by ephrinA5 stimulation-triggered reduction of Snhg15 expression. Hence, we here propose a triple helix recognition mechanism, underlying cell motility regulation via lncRNA-targeted DNA methylation in a clinically relevant context.

Genetic landscape of congenital insensitivity to pain and hereditary sensory and autonomic neuropathies.

Congenital insensitivity to pain (CIP) and hereditary sensory and autonomic neuropathies (HSAN) are clinically and genetically heterogeneous disorders exclusively or predominantly affecting the sensory and autonomic neurons. Due to the rarity of the diseases and findings based mainly on single case reports or small case series, knowledge about these disorders is limited. Here, we describe the molecular workup of a large international cohort of CIP/HSAN patients including patients from normally under-represented countries. We identify 80 previously unreported pathogenic or likely pathogenic variants in a total of 73 families in the >20 known CIP/HSAN-associated genes. The data expand the spectrum of disease-relevant alterations in CIP/HSAN, including novel variants in previously rarely recognized entities such as ATL3-, FLVCR1- and NGF-associated neuropathies and previously under-recognized mutation types such as larger deletions. In silico predictions, heterologous expression studies, segregation analyses and metabolic tests helped to overcome limitations of current variant classification schemes that often fail to categorize a variant as disease-related or benign. The study sheds light on the genetic causes and disease-relevant changes within individual genes in CIP/HSAN. This is becoming increasingly important with emerging clinical trials investigating subtype or gene-specific treatment strategies.

Closing the Gap - Detection of 5q-Spinal Muscular Atrophy by Short-Read Next-Generation Sequencing and Unexpected Results in a Diagnostic Patient Cohort.

BACKGROUND: The importance of early diagnosis of 5q-Spinal muscular atrophy (5q-SMA) has heightened as early intervention can significantly improve clinical outcomes. In 96% of cases, 5q-SMA is caused by a homozygous deletion of SMN1. Around 4 % of patients carry a SMN1 deletion and a single-nucleotide variant (SNV) on the other allele. Traditionally, diagnosis is based on multiplex ligation probe amplification (MLPA) to detect homozygous or heterozygous exon 7 deletions in SMN1. Due to high homologies within the SMN1/SMN2 locus, sequence analysis to identify SNVs of the SMN1 gene is unreliable by standard Sanger or short-read next-generation sequencing (srNGS) methods. OBJECTIVE: The objective was to overcome the limitations in high-throughput srNGS with the aim of providing SMA patients with a fast and reliable diagnosis to enable their timely therapy. METHODS: A bioinformatics workflow to detect homozygous SMN1 deletions and SMN1 SNVs on srNGS analysis was applied to diagnostic whole exome and panel testing for suggested neuromuscular disorders (1684 patients) and to fetal samples in prenatal diagnostics (260 patients). SNVs were detected by aligning sequencing reads from SMN1 and SMN2 to an SMN1 reference sequence. Homozygous SMN1 deletions were identified by filtering sequence reads for the ,, gene-determining variant" (GDV). RESULTS: 10 patients were diagnosed with 5q-SMA based on (i) SMN1 deletion and hemizygous SNV (2 patients), (ii) homozygous SMN1 deletion (6 patients), and (iii) compound heterozygous SNVs in SMN1 (2 patients). CONCLUSIONS: Applying our workflow in srNGS-based panel and whole exome sequencing (WES) is crucial in a clinical laboratory, as otherwise patients with an atypical clinical presentation initially not suspected to suffer from SMA remain undiagnosed.

Molecular characterisation of 36 multilocus imprinting disturbance (MLID) patients: a comprehensive approach.

BACKGROUND: Imprinting disorders (ImpDis) comprise diseases which are caused by aberrant regulation of monoallelically and parent-of-origin-dependent expressed genes. A characteristic molecular change in ImpDis patients is aberrant methylation signatures at disease-specific loci, without an obvious DNA change at the specific differentially methylated region (DMR). However, there is a growing number of reports on multilocus imprinting disturbances (MLIDs), i.e. aberrant methylation at different DMRs in the same patient. These MLIDs account for a significant number of patients with specific ImpDis, and several reports indicate a central role of pathogenic maternal effect variants in their aetiology by affecting the maturation of the oocyte and the early embryo. Though several studies on the prevalence and the molecular causes of MLID have been conducted, homogeneous datasets comprising both genomic and methylation data are still lacking. RESULTS: Based on a cohort of 36 MLID patients, we here present both methylation data obtained from next-generation sequencing (NGS, ImprintSeq) approaches and whole-exome sequencing (WES). The compilation of methylation data did not reveal a disease-specific MLID episignature, and a predisposition for the phenotypic modification was not obvious as well. In fact, this lack of epigenotype-phenotype correlation might be related to the mosaic distribution of imprinting defects and their functional relevance in specific tissues. CONCLUSIONS: Due to the higher sensitivity of NGS-based approaches, we suggest that ImprintSeq might be offered at reference centres in case of ImpDis patients with unusual phenotypes but MLID negative by conventional tests. By WES, additional MLID causes than the already known maternal effect variants could not be identified, neither in the patients nor in the maternal exomes. In cases with negative WES results, it is currently unclear to what extent either environmental factors or undetected genetic variants contribute to MLID.

Functional connectivity signatures of NMDAR dysfunction in schizophrenia-integrating findings from imaging genetics and pharmaco-fMRI.

Both, pharmacological and genome-wide association studies suggest N-methyl-D-aspartate receptor (NMDAR) dysfunction and excitatory/inhibitory (E/I)-imbalance as a major pathophysiological mechanism of schizophrenia. The identification of shared fMRI brain signatures of genetically and pharmacologically induced NMDAR dysfunction may help to define biomarkers for patient stratification. NMDAR-related genetic and pharmacological effects on functional connectivity were investigated by integrating three different datasets: (A) resting state fMRI data from 146 patients with schizophrenia genotyped for the disease-associated genetic variant rs7191183 of GRIN2A (encoding the NMDAR 2 A subunit) as well as 142 healthy controls. (B) Pharmacological effects of the NMDAR antagonist ketamine and the GABA-A receptor agonist midazolam were obtained from a double-blind, crossover pharmaco-fMRI study in 28 healthy participants. (C) Regional gene expression profiles were estimated using a postmortem whole-brain microarray dataset from six healthy donors. A strong resemblance was observed between the effect of the genetic variant in schizophrenia and the ketamine versus midazolam contrast of connectivity suggestive for an associated E/I-imbalance. This similarity became more pronounced for regions with high density of NMDARs, glutamatergic neurons, and parvalbumin-positive interneurons. From a functional perspective, increased connectivity emerged between striato-pallido-thalamic regions and cortical regions of the auditory-sensory-motor network, while decreased connectivity was observed between auditory (superior temporal gyrus) and visual processing regions (lateral occipital cortex, fusiform gyrus, cuneus). Importantly, these imaging phenotypes were associated with the genetic variant, the differential effect of ketamine versus midazolam and schizophrenia (as compared to healthy controls). Moreover, the genetic variant was associated with language-related negative symptomatology which correlated with disturbed connectivity between the left posterior superior temporal gyrus and the superior lateral occipital cortex. Shared genetic and pharmacological functional connectivity profiles were suggestive of E/I-imbalance and associated with schizophrenia. The identified brain signatures may help to stratify patients with a common molecular disease pathway providing a basis for personalized psychiatry.

New Insights into the Neuromyogenic Spectrum of a Gain of Function Mutation in SPTLC1.

Serine palmitoyltransferase long chain base subunit 1 (SPTLC1) encodes a serine palmitoyltransferase (SPT) resident in the endoplasmic reticulum (ER). Pathological SPTLC1 variants cause a form of hereditary sensory and autonomic neuropathy (HSAN1A), and have recently been linked to unrestrained sphingoid base synthesis, causing a monogenic form of amyotrophic lateral sclerosis (ALS). It was postulated that the phenotypes associated with dominant variants in SPTLC1 may represent a continuum between neuropathy and ALS in some cases, complicated by additional symptoms such as cognitive impairment. A biochemical explanation for this clinical observation does not exist. By performing proteomic profiling on immortalized lymphoblastoid cells derived from one patient harbouring an alanine to serine amino acid substitution at position 20, we identified a subset of dysregulated proteins playing significant roles in neuronal homeostasis and might have a potential impact on the manifestation of symptoms. Notably, the identified p.(A20S)-SPTLC1 variant is associated with decrease of transcript and protein level. Moreover, we describe associated muscle pathology findings, including signs of mild inflammation accompanied by dysregulation of respective markers on both the protein and transcript levels. By performing coherent anti-Stokes Raman scattering microscopy, presence of protein and lipid aggregates could be excluded.

Biallelic loss-of-function variants in WDR11 are associated with microcephaly and intellectual disability.

Heterozygous missense variants in the WD repeat domain 11 (WDR11) gene are associated with hypogonadotropic hypogonadism in humans. In contrast, knockout of both alleles of Wdr11 in mice results in a more severe phenotype with growth and developmental delay, features of holoprosencephaly, heart defects and reproductive disorders. Similar developmental defects known to be associated with aberrant hedgehog signaling and ciliogenesis have been found in zebrafish after Wdr11 knockdown. We here report biallelic loss-of-function variants in the WDR11 gene in six patients from three independent families with intellectual disability, microcephaly and short stature. The findings suggest that biallelic WDR11 variants in humans result in an overlapping but milder phenotype compared to Wdr11-deficient animals. However, the observed human phenotype differs significantly from dominantly inherited variants leading to hypogonadotropic hypogonadism, suggesting that recessive WDR11 variants result in a clinically distinct entity.

C2orf69 mutations disrupt mitochondrial function and cause a multisystem human disorder with recurring autoinflammation.

BACKGROUNDDeciphering the function of the many genes previously classified as uncharacterized open reading frame (ORF) would complete our understanding of a cell's function and its pathophysiology.METHODSWhole-exome sequencing, yeast 2-hybrid and transcriptome analyses, and molecular characterization were performed in this study to uncover the function of the C2orf69 gene.RESULTSWe identified loss-of-function mutations in the uncharacterized C2orf69 gene in 8 individuals with brain abnormalities involving hypomyelination and microcephaly, liver dysfunction, and recurrent autoinflammation. C2orf69 contains an N-terminal signal peptide that is required and sufficient for mitochondrial localization. Consistent with mitochondrial dysfunction, the patients showed signs of respiratory chain defects, and a CRISPR/Cas9-KO cell model of C2orf69 had similar respiratory chain defects. Patient-derived cells revealed alterations in immunological signaling pathways. Deposits of periodic acid-Schiff-positive (PAS-positive) material in tissues from affected individuals, together with decreased glycogen branching enzyme 1 (GBE1) activity, indicated an additional impact of C2orf69 on glycogen metabolism.CONCLUSIONSOur study identifies C2orf69 as an important regulator of human mitochondrial function and suggests that this gene has additional influence on other metabolic pathways.

Paternal 132 bp deletion affecting KCNQ1OT1 in 11p15.5 is associated with growth retardation but does not affect imprinting.

BACKGROUND: The chromosomal region 11p15.5 harbours two imprinting centres (H19/IGF2:IG-DMR/IC1, KCNQ1OT1:TSS-DMR/IC2). Molecular alterations of the IC2 are associated with Beckwith-Wiedemann syndrome (BWS), whereas only single patients with growth retardation and Silver-Russell syndrome (SRS) features have been reported. CNVs in 11p15.5 account for less than 1% of patients with BWS and SRS, and they mainly consist of duplications of both ICs either affecting the maternal (SRS) or the paternal (BWS) allele. However, this correlation does not apply to smaller CNVs, which are associated with diverse clinical outcomes. METHODS AND RESULTS: We identified a family with a 132 bp deletion within the KCNQ1OT1 gene, associated with growth retardation in case of paternal transmission but a normal phenotype when maternally inherited. Comparison of molecular and clinical data with cases from the literature helped to delineate its functional relevance. CONCLUSION: Microdeletions within the paternal IC2 affecting the KCNQ1OT1 gene have been described in only five families, and they all include the differentially methylated region KCNQ1OT1:TSS-DMR/IC2 and parts of the KCNQ1 gene. However, these deletions have different impacts on the expression of both genes and the cell-cycle inhibitor CDKN1C. They thereby cause different phenotypes. The 132 bp deletion is the smallest deletion in the IC2 reported so far. It does not affect the IC2 methylation in general and the coding sequence of the KCNQ1 gene. Thus, the deletion is only associated with a growth retardation phenotype when paternally transmitted but not with other clinical features in case of maternal inheritance as observed for larger deletions.

Heterogeneous phenotypes in families with duplications of the paternal allele within the imprinting center 1 (H19/IGF2:TSS-DMR) in 11p15.5.

The clinical impact of duplications affecting the 11p15.5 region is difficult to predict, and depends on the parent-of-origin of the affected allele as well as on the type (deletion, duplication), the extent and genomic content of the variant. Three unrelated families with inheritance of duplications affecting the IC1 region in 11p15.5 through two generations but different phenotypes (Beckwith-Wiedemann and Silver-Russell syndromes, normal phenotype) are reported. The inconsistent phenotypic patterns of carriers of the same variant strongly indicate the impact of cis- and/or trans-acting modifiers on the clinical outcome of IC1 duplication carriers.

Loss of supervillin causes myopathy with myofibrillar disorganization and autophagic vacuoles.

The muscle specific isoform of the supervillin protein (SV2), encoded by the SVIL gene, is a large sarcolemmal myosin II- and F-actin-binding protein. Supervillin (SV2) binds and co-localizes with costameric dystrophin and binds nebulin, potentially attaching the sarcolemma to myofibrillar Z-lines. Despite its important role in muscle cell physiology suggested by various in vitro studies, there are so far no reports of any human disease caused by SVIL mutations. We here report four patients from two unrelated, consanguineous families with a childhood/adolescence onset of a myopathy associated with homozygous loss-of-function mutations in SVIL. Wide neck, anteverted shoulders and prominent trapezius muscles together with variable contractures were characteristic features. All patients showed increased levels of serum creatine kinase but no or minor muscle weakness. Mild cardiac manifestations were observed. Muscle biopsies showed complete loss of large supervillin isoforms in muscle fibres by western blot and immunohistochemical analyses. Light and electron microscopic investigations revealed a structural myopathy with numerous lobulated muscle fibres and considerable myofibrillar alterations with a coarse and irregular intermyofibrillar network. Autophagic vacuoles, as well as frequent and extensive deposits of lipoproteins, including immature lipofuscin, were observed. Several sarcolemma-associated proteins, including dystrophin and sarcoglycans, were partially mis-localized. The results demonstrate the importance of the supervillin (SV2) protein for the structural integrity of muscle fibres in humans and show that recessive loss-of-function mutations in SVIL cause a distinctive and novel myopathy.

Long-read sequencing to understand genome biology and cell function.

Determining the sequence of DNA and RNA molecules has a huge impact on the understanding of cell biology and function. Recent advancements in next-generation short-read sequencing (NGS) technologies, drops in cost and a resolution down to the single-cell level shaped our current view on genome structure and function. Third-generation sequencing (TGS) methods further complete the knowledge about these processes based on long reads and the ability to analyze DNA or RNA at single molecule level. Long-read sequencing provides additional possibilities to study genome architecture and the composition of highly complex regions and to determine epigenetic modifications of nucleotide bases at a genome-wide level. We discuss the principles and advancements of long-read sequencing and its applications in genome biology.

Inherited cases of CNOT3-associated intellectual developmental disorder with speech delay, autism, and dysmorphic facies.

De novo pathogenic variants in CNOT3 have recently been reported in a developmental delay disorder (intellectual developmental disorder with speech delay, autism, and dysmorphic facies [IDDSADF, OMIM: #618672]). The patients present with a variable degree of developmental delay and behavioral problems. To date, all reported disease-causing variants occurred de novo and no parent-child transmission was observed. We report for the first time autosomal dominant transmissions of the CNOT3-associated developmental disorder in two unrelated families. The clinical characteristics in our patients match the IDDSADF features reported so far and suggest substantial variability of the phenotype within the same family.

Thyroid hormone induces cellular senescence in prostate cancer cells through induction of DEC1.

While several studies link a state of hypothyroidism to extended lifespan of humans and mice, the role of thyroid hormone in cancer is more controversial since tumor-promoting as well as tumor-suppressive effects are known. In general, aberrant thyroid hormone levels are associated with increased cancer incidence. For prostate cancer (PCa) a prospective cohort study indicates that lower thyrotropin (TSH) and higher thyroxin (T4) levels are associated with an increased risk of PCa. However, triiodothyronine (T3) can attenuate PCa progression. Here we show that T3 treatment of human PCa cells reduces cell proliferation, by induction of cellular senescence. Interestingly, we could neither detect an increased expression of p16INK4A nor p21CIP1 cell cycle inhibitors, which are mediators of the two major pathways for senescence induction. This suggests that the T3-induced cellular senescence of PCa cells is driven by an alternative pathway. We show that T3-mediated cellular senescence is associated with increase of DEC1 expression encoded by the BHLHE40 gene and p15INK4B encoded by CDKN2B. Each DEC1/BHLHE40 and p15INK4B/CDKN2B knockdown reduced significantly the level of T3-mediated cellular senescence. The data suggest that DEC1 and p15INK4B are crucial for the T3-induced cellular senescence. In line with a protective role of cellular senescence in cancer, public databases provide evidence linking low DEC1 expression to poor survival of PCa patients. Further we show that the BHLHE40 promoter is responsive to T3 suggesting BHLHE40 being a target gene for the thyroid hormone receptor (TR). Taken together, the data suggest that T3 mediates cellular senescence in PCa cells through induction of DEC1- and p15INK4B -dependent pathway.

HMGA2 Variants in Silver-Russell Syndrome: Homozygous and Heterozygous Occurrence.

CONTEXT: Silver-Russell syndrome (SRS) is a clinical and molecular heterogeneous disorder associated with short stature, typical facial gestalt, and body asymmetry. Though molecular causes of SRS can be identified in a significant number of patients, about one-half of patients currently remain without a molecular diagnosis. However, determination of the molecular cause is required for a targeted treatment and genetic counselling. OBJECTIVE: The aim of this study was to corroborate the role of HMGA2 as an SRS-causing gene and reevaluate its mode of inheritance. DESIGN, SETTING, PATIENTS: Patients were part of an ongoing study aiming on SRS-causing genes. They were classified according to the Netchine-Harbison clinical scoring system, and DNA samples were investigated by whole exome sequencing. Common molecular causes of SRS were excluded before. RESULTS: Three novel pathogenic HMGA2 variants were identified in 5 patients from 3 SRS families, and fulfilling diagnostic criteria of SRS. For the first time, homozygosity for a variant in HMGA2 could be identified in a severely affected sibpair, whereas parents carrying heterozygous variants had a mild phenotype. Treatment with recombinant growth hormone led to a catch-up growth in 1 patient, whereas all others did not receive growth hormone and stayed small. One patient developed type 2 diabetes at age 30 years. CONCLUSIONS: Identification of novel pathogenic variants confirms HMGA2 as an SRS-causing gene; thus, HMGA2 testing should be implemented in molecular SRS diagnostic workup. Furthermore, inheritance of HMGA2 is variable depending on the severity of the variant and its consequence for protein function.

Germline GPR161 Mutations Predispose to Pediatric Medulloblastoma.

PURPOSE: The identification of a heritable tumor predisposition often leads to changes in management and increased surveillance of individuals who are at risk; however, for many rare entities, our knowledge of heritable predisposition is incomplete. METHODS: Families with childhood medulloblastoma, one of the most prevalent childhood malignant brain tumors, were investigated to identify predisposing germline mutations. Initial findings were extended to genomes and epigenomes of 1,044 medulloblastoma cases from international multicenter cohorts, including retrospective and prospective clinical studies and patient series. RESULTS: We identified heterozygous germline mutations in the G protein-coupled receptor 161 (GPR161) gene in six patients with infant-onset medulloblastoma (median age, 1.5 years). GPR161 mutations were exclusively associated with the sonic hedgehog medulloblastoma (MBSHH) subgroup and accounted for 5% of infant MBSHH cases in our cohorts. Molecular tumor profiling revealed a loss of heterozygosity at GPR161 in all affected MBSHH tumors, atypical somatic copy number landscapes, and no additional somatic driver events. Analysis of 226 MBSHH tumors revealed somatic copy-neutral loss of heterozygosity of chromosome 1q as the hallmark characteristic of GPR161 deficiency and the primary mechanism for biallelic inactivation of GPR161 in affected MBSHH tumors. CONCLUSION: Here, we describe a novel brain tumor predisposition syndrome that is caused by germline GPR161 mutations and characterized by MBSHH in infants. Additional studies are needed to identify a potential broader tumor spectrum associated with germline GPR161 mutations.

Unstable TTTTA/TTTCA expansions in MARCH6 are associated with Familial Adult Myoclonic Epilepsy type 3.

Familial Adult Myoclonic Epilepsy (FAME) is a genetically heterogeneous disorder characterized by cortical tremor and seizures. Intronic TTTTA/TTTCA repeat expansions in SAMD12 (FAME1) are the main cause of FAME in Asia. Using genome sequencing and repeat-primed PCR, we identify another site of this repeat expansion, in MARCH6 (FAME3) in four European families. Analysis of single DNA molecules with nanopore sequencing and molecular combing show that expansions range from 3.3 to 14 kb on average. However, we observe considerable variability in expansion length and structure, supporting the existence of multiple expansion configurations in blood cells and fibroblasts of the same individual. Moreover, the largest expansions are associated with micro-rearrangements occurring near the expansion in 20% of cells. This study provides further evidence that FAME is caused by intronic TTTTA/TTTCA expansions in distinct genes and reveals that expansions exhibit an unexpectedly high somatic instability that can ultimately result in genomic rearrangements.