Biallelic Loss Of Function Mutations Research Articles

An extensive in silico analysis of missense mutations of the human AIMP2 gene

HLD17 (Hypomyelinating Leukodystrophy 17) is an inherited white matter disorder characterized by insufficient myelin production due to biallelic loss of function mutations in the aminoacyl-tRNA synthetase complex-interacting multifunctional protein 2 (AIMP2) gene. In silico analysis of SNVs (single nucleotide variants) in the AIMP2 gene is an efficient and cost-effective method for analyzing and predicting the impact of mutations on protein function and disease pathophysiology.The study used dbSNP and Ensembl databases to obtain data on 343 nonsynonymous single nucleotide variants (nsSNVs) in the human AIMP2 gene. Six prediction algorithm tools were used to assess the effects of these nsSNVs on AIMP2's functions and structures. Results showed that 18 nsSNVs were located within functional domains, while 10 nsSNVs led to decreased protein stability. The structural and functional properties of the AIMP2 protein were investigated using databases such as Predict Protein, Mutpred2, and HOPE. ConSurf analysis provided information about conserved nsSNVs. GeneMANIA and STRING software tools were used to predict interactions between gene-gene and protein-protein, respectively. Phyre2 and I-TASSER web servers were used to predict the 3D structures of wild-type and mutant proteins.In addition, having the challenge of probable post-translational modification sites in the AIMP2, we made predictions using various bioinformatics tools. Consecuently, three minor mutations (L138Q, V161E, and I188N) and five major mutations (C23S, D121G, I122S, P128S, and W268S) were found to affect the AIMP2 protein's structure or function. Anyway, These mutations need to be further studied and confirmed through experimental investigation and GWAS studies.

Reduction of Filamin C Results in Altered Proteostasis, Cardiomyopathy, and Arrhythmias.

Many cardiomyopathy-associated FLNC pathogenic variants are heterozygous truncations, and FLNC pathogenic variants are associated with arrhythmias. Arrhythmia triggers in filaminopathy are incompletely understood. We describe an individual with biallelic FLNC pathogenic variants, p.Arg650X and c.970-4A>G, with peripartum cardiomyopathy and ventricular arrhythmias. We also describe clinical findings in probands with FLNC variants including Val2715fs87X, Glu2458Serfs71X, Phe106Leu, and c.970-4A>G with hypertrophic and dilated cardiomyopathy, atrial fibrillation, and ventricular tachycardia. Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) were generated. The FLNC truncation, Arg650X/c.970-4A>G, showed a marked reduction in filamin C protein consistent with biallelic loss of function mutations. To assess loss of filamin C, gene editing of a healthy control iPSC line was used to generate a homozygous FLNC disruption in the actin binding domain. Because filamin C has been linked to protein quality control, we assessed the necessity of filamin C in iPSC-CMs for response to the proteasome inhibitor bortezomib. After exposure to low-dose bortezomib, FLNC-null iPSC-CMs showed an increase in the chaperone proteins BAG3, HSP70 (heat shock protein 70), and HSPB8 (small heat shock protein B8) and in the autophagy marker LC3I/II. FLNC null iPSC-CMs had prolonged electric field potential, which was further prolonged in the presence of low-dose bortezomib. FLNC null engineered heart tissues had impaired function after low-dose bortezomib. FLNC pathogenic variants associate with a predisposition to arrhythmias, which can be modeled in iPSC-CMs. Reduction of filamin C prolonged field potential, a surrogate for action potential, and with bortezomib-induced proteasome inhibition, reduced filamin C led to greater arrhythmia potential and impaired function.

Vitamin D3 deficiency and osteopenia in spastic paraplegia type 5 indicate impaired bone homeostasis

Hereditary spastic paraplegia type 5 (SPG5) is an autosomal recessively inherited movement disorder characterized by progressive spastic gait disturbance and afferent ataxia. SPG5 is caused by bi-allelic loss of function mutations in CYP7B1 resulting in accumulation of the oxysterols 25-hydroxycholesterol and 27-hydroxycholesterol in serum and cerebrospinal fluid of SPG5 patients. An effect of 27- hydroxycholesterol via the estrogen and liver X receptors was previously shown on bone homeostasis. This study analyzed bone homeostasis and osteopenia in 14 SPG5 patients as a non-motor feature leading to a potential increased risk for bone fractures. T-Scores in CT bone density measurements were reduced, indicating osteopenia in SPG5 patients. Further, we analyzed various metabolites of bone homeostasis by ELISA in serum samples of these patients. We identified a lack of vitamin D3 metabolites (Calcidiol and Calcitriol), an increase in Sclerostin as a bone formation/mineralization inhibiting factor, and a decrease in cross-linked N-telopeptide of type I collagen (NTX), a marker indicating reduced bone resorption. As statin treatment has been found to lower oxysterol levels, we evaluated its effect in samples of the STOP-SPG5 trial and found atorvastatin to normalize the increased sclerostin levels. In summary, our study identified osteopenia as a non-motor feature in SPG5 and suggests the need for vitamin D3 substitution in SPG5 patients. Sclerostin may be considered a therapeutic target and biomarker in upcoming therapeutical trials in SPG5.

Ablation of Iron Regulatory Protein 2 produces a neurological disorder characterized by motor, somatosensory, and executive dysfunction in mice

Iron is an important cofactor for many proteins and is used to create Fe-S clusters and heme prosthetic groups that enzymes use to catalyze enzymatic reactions. Proteins involved in the import, export, and sequestration of iron are regulated by Iron Regulatory Proteins (IRPs). Recently, a patient with bi-allelic loss of function mutations in IREB2 leading to the absence of IRP2 protein was discovered. The patient failed to achieve developmental milestones and was diagnosed with dystonic cerebral palsy, epilepsy, microcytic hypochromic anemia, and frontal lobe atrophy. Several more IREB2 deficient patients subsequently identified manifested similar neurological problems. To better understand the manifestations of this novel neurological disease, we subjected an Irp2-null mouse model to extensive behavioral testing. Irp2-null mice had a significant motor deficit demonstrated by reduced performance on rotarod and hanging wire tests. Somatosensory function was also compromised in hot and cold plate assays. Their spatial search strategy was impaired in the Barnes maze and they exhibited a difficulty in flexibly adapting their response in the operant touchscreen reversal learning task. The latter is a cognitive behavior known to require an intact prefrontal cortex. These results suggest that loss of Irp2 in mice causes motor and behavioral deficits that faithfully reflect the IREB2 patient's neurodegenerative disorder.

Safe use of the ketogenic diet in an infant with microcephaly, epilepsy, and diabetes syndrome: a case report

BackgroundMicrocephaly, epilepsy, and diabetes syndrome (MEDS) is a rare syndromic form of monogenic diabetes caused by bi-allelic loss of function mutations in IER3IP1. In vitro studies have shown that loss of IER31P leads to apoptosis in both neurons and pancreatic β-cells. Simultaneous management of seizures and diabetes is challenging in patients with MEDS. We present the challenges and successes in the use of ketogenic diet in an infant with insulinopenic diabetes.Case presentationOur term female proband presented at 2 months of age with new onset multifocal seizures followed by the onset of infantile spasms (IS) at 4 months of age. An epilepsy gene panel identified bi-allelic variants, c.239T > G (p.Leu80*) and c.2T > A (initiator codon), in IER3IP1 that were subsequently shown to be inherited in trans. Following initiation of steroid therapy for IS, the patient developed clinically apparent insulin requiring diabetes. Her epilepsy was ultimately refractory to multiple antiseizure medications, thus the ketogenic diet (KD) was initiated. We were able to successfully titrate to a therapeutic KD ratio of 3:1 and maintain a ketotic state without diabetic ketoacidosis (DKA). With intercurrent illnesses, however, the patient had rapid decompensation and mild DKA due to delays in treatment, and for this reason, KD was discontinued after 5 months.ConclusionsWe report two novel IER31P1 mutations in a patient with MEDS and the successful management of the cooccurring conditions of IS and insulinopenic diabetes with the KD. Our experience underscores the importance of careful monitoring during KD as our patient had DKA more easily when on the KD.

β-Glucocerebrosidase Deficiency Activates an Aberrant Lysosome-Plasma Membrane Axis Responsible for the Onset of Neurodegeneration.

β-glucocerebrosidase is a lysosomal hydrolase involved in the catabolism of the sphingolipid glucosylceramide. Biallelic loss of function mutations in this enzyme are responsible for the onset of Gaucher disease, while monoallelic β-glucocerebrosidase mutations represent the first genetic risk factor for Parkinson’s disease. Despite this evidence, the molecular mechanism linking the impairment in β-glucocerebrosidase activity with the onset of neurodegeneration in still unknown. In this frame, we developed two in vitro neuronal models of β-glucocerebrosidase deficiency, represented by mouse cerebellar granule neurons and human-induced pluripotent stem cells-derived dopaminergic neurons treated with the specific β-glucocerebrosidase inhibitor conduritol B epoxide. Neurons deficient for β-glucocerebrosidase activity showed a lysosomal accumulation of glucosylceramide and the onset of neuronal damage. Moreover, we found that neurons react to the lysosomal impairment by the induction of their biogenesis and exocytosis. This latter event was responsible for glucosylceramide accumulation also at the plasma membrane level, with an alteration in lipid and protein composition of specific signaling microdomains. Collectively, our data suggest that β-glucocerebrosidase loss of function impairs the lysosomal compartment, establishing a lysosome–plasma membrane axis responsible for modifications in the plasma membrane architecture and possible alterations of intracellular signaling pathways, leading to neuronal damage.

Human induced pluripotent stem cells generated from Chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature (CANDLE) syndrome patients with a homozygous mutation in the PSMB8 gene (NIHTVBi016-A, NIHTVBi017-A, NIHTVBi018-A)

We have successfully generated induced pluripotent stem cells (iPSC) from dermal fibroblasts and peripheral blood mononuclear cells from patients with a homozygous missense mutation in the gene encoding PSMB8. Biallelic loss of function mutations in this gene are responsible for the PSMB8 deficiency termed Chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature (CANDLE). The iPSC carrying the homozygous PSMB8 gene mutation (c.224C > T, T75M) are phenotypically normal and have the capacity to differentiate toward the three germ layers. These iPSC have great potential to study the role of PMSB8 in the regulation of immune responses and other cellular pathways.

Nav1.7 is required for normal C-low threshold mechanoreceptor function in humans and mice.

Patients with bi-allelic loss of function mutations in the voltage-gated sodium channel Nav1.7 present with congenital insensitivity to pain (CIP), whilst low threshold mechanosensation is reportedly normal. Using psychophysics (n = 6 CIP participants and n = 86 healthy controls) and facial electromyography (n = 3 CIP participants and n = 8 healthy controls), we found that these patients also have abnormalities in the encoding of affective touch, which is mediated by the specialized afferents C-low threshold mechanoreceptors (C-LTMRs).In the mouse, we found that C-LTMRs express high levels of Nav1.7. Genetic loss or selective pharmacological inhibition of Nav1.7 in C-LTMRs resulted in a significant reduction in the total sodium current density, an increased mechanical threshold and reduced sensitivity to non-noxious cooling. The behavioural consequence of loss of Nav1.7 in C-LTMRs in mice was an elevation in the von Frey mechanical threshold and less sensitivity to cooling on a thermal gradient.Nav1.7 is therefore not only essential for normal pain perception but also for normal C-LTMR function, cool sensitivity and affective touch.

Heading towards a dead end: The role of DND1 in germ line differentiation of human iPSCs.

The DND microRNA-mediated repression inhibitor 1 (DND1) is a conserved RNA binding protein (RBP) that plays important roles in survival and fate maintenance of primordial germ cells (PGCs) and in the development of the male germline in zebrafish and mice. Dead end was shown to be expressed in human pluripotent stem cells (PSCs), PGCs and spermatogonia, but little is known about its specific role concerning pluripotency and human germline development. Here we use CRISPR/Cas mediated knockout and PGC-like cell (PGCLC) differentiation in human iPSCs to determine if DND1 (1) plays a role in maintaining pluripotency and (2) in specification of PGCLCs. We generated several clonal lines carrying biallelic loss of function mutations and analysed their differentiation potential towards PGCLCs and their gene expression on RNA and protein levels via RNA sequencing and mass spectrometry. The generated knockout iPSCs showed no differences in pluripotency gene expression, proliferation, or trilineage differentiation potential, but yielded reduced numbers of PGCLCs as compared with their parental iPSCs. RNAseq analysis of mutated PGCLCs revealed that the overall gene expression remains like non-mutated PGCLCs. However, reduced expression of genes associated with PGC differentiation and maintenance (e.g., NANOS3, PRDM1) was observed. Together, we show that DND1 iPSCs maintain their pluripotency but exhibit a reduced differentiation to PGCLCs. This versatile model will allow further analysis of the specific mechanisms by which DND1 influences PGC differentiation and maintenance.

Bi-allelic loss of function variants in GOLGA2 are associated with a complex neurological phenotype: Report of a second family.

GOGLA2/GM130 is a Golgin protein involved in vesicle tethering, cell proliferation and autophagy. Recessive loss of function mutation in GOLGA2 has been previously reported in a single family with muscular dystrophy and microcephaly. Here we describe a second consanguineous family with the bi-allelic loss of function mutations in GOLGA2. The patient exhibits microcephaly, seizures, and myopathy similar to the previously reported patient with GOLGA2 mutation. This report supports the critical developmental requirement of GOLGA2 and emphasizes a similar and severe clinical presentation with loss of function mutations in affected patients.

Expanding the Phenotype of TRMT10A Mutations: Case Report and a Review of the Existing Cases

The tRNA methyltransferase 10 homologue A (TRMT10A) gene encodes tRNA methyl transferase, and biallelic loss of function mutations cause a recessive syndrome of intellectual disability, microcephaly, short stature and diabetes. A case with intellectual disability and distinctive features including microcephaly was admitted. She was diagnosed with epilepsy at 2.5 years old. At 3.6 years of age, severe short stature related to growth hormone (GH) deficiency was detected. She had an incidental diagnosis of diabetes at age 11.4 years which was negative for diabetes antibodies with persistent C-peptide level and she was treated with metformin. Spontaneous puberty did not begin until 15.7 years of age and she was found to have primary ovarian failure. A homozygous p.Arg127* mutation in TRMT10A was detected. In addition to the typical clinical features which characterize TRMT10A syndrome, we observed an unusual form of impaired glucose metabolism which presented in early childhood with hypoglycemia followed by diabetes in late childhood. GH deficiency and primary ovarian failure may also be additional findings of this syndrome. Patients with slow onset diabetes who are negative for auto-antibodies and have extra-pancreatic features should be tested for all known subtypes of monogenic diabetes.

Age-dependent neurological phenotypes in a mouse model of PRRT2-related diseases

Paroxysmal kinesigenic dyskinesia is an episodic movement disorder caused by dominant mutations in the proline-rich transmembrane protein PRRT2, with onset in childhood and typically with improvement or resolution by middle age. Mutations in the same gene may also cause benign infantile seizures, which begin in the first year of life and typically remit by the age of 2 years. Many details of PRRT2 function at the synapse, and the effects of mutations on neuronal excitability in the pathophysiology of epilepsy and dyskinesia, have emerged through the work of several groups over the last decade. However, the age dependence of the phenotypes has not been explored in detail in transgenic models. Here, we report our findings in heterozygous and homozygous Prrt2 knockout mice that recapitulate the age dependence of dyskinesia seen in the human disease. We show that Prrt2 deletion reduces the levels of synaptic proteins in a dose-dependent manner that is most pronounced at postnatal day 5 (P5), attenuates at P60, and disappears by P180. In a test for foot slippage while crossing a balance beam, transient loss of coordination was most pronounced at P60 and less prominent at age extremes. Slower traverse time was noted in homozygous knockout mice only, consistent with the ataxia seen in rare individuals with biallelic loss of function mutations in Prrt2. We thus identify three age-dependent phenotypic windows in the mouse model, which recapitulate the pattern seen in humans with PRRT2-related diseases.

Acantholytic dyskeratotic epidermal naevus and striate palmoplantar keratoderma associated with DSG1 mutation: evidence for segmental type 2 mosaicism

Striate palmoplantar keratoderma (SPPK) is a rare autosomal-dominant form of PPK, characterized by linear hyperkeratosis of the volar aspects of the fingers extending onto the palm and focal to diffuse hyperkeratosis of the soles. The type 1 of SPPK (MIM148700) is associated with heterozygous mutations in desmoglein1 (DSG1) (1).Skin manifestations are generally limited to palms and soles (2-4). In contrast, bi-allelic loss of function mutations of DSG1 have been shown to be responsible for the severe dermatitis, multiple allergies and metabolic wasting (SAM syndrome) (5,6).

Human induced pluripotent stem cells generated from a patient with a homozygous L272P mutation in the OTULIN gene (NIHTVBi014-A).

We have successfully generated induced pluripotent stem cells (iPSC) from dermal fibroblasts of a patient with a homozygous p.Leu272Pro mutation in the gene encoding the linear deubiquitinase OTULIN. Biallelic loss of function mutations in this gene are responsible for the OTULIN deficiency termed Otulipenia or OTULIN-related autoinflammatory syndrome (ORAS). The iPSC carrying homozygous L272P OTULIN gene mutations are phenotypically normal and they have capacity to differentiate toward the three germ layers. These iPSC have great potential to study the role of linear ubiquitination in the regulation of immune responses and other cellular pathways.

Deciphering molecular characters of multiple lung lesion using comprehensive genomic profiling and its association of histology.

e21051 Background: Differentiating multiple pulmonary lesions as multiple primary lung cancer (MLC) or intra-pulmonary metastasis (IPM) is critical for clinics. Radiological or histological (dis)concordance may be informative, while, genetic information may aid tracing lineage information on multiple lung lesions. This study aims to apply comprehensive genomic profiling deciphering intrinsic genetics of multiple lung lesions. Methods: 32 patients, 69 FFPE samples were applied to perform high-through put sequencing. 636 cancer-related genes were captured and sequenced by MGI-seq 2000. Raw data was processed via in-house developed pipeline. Unsupervised clustering was applied to cluster samples based on genetic characters after variant calling and annotation. Patients were categorized into “Genomic related” and “Genomic unrelated” groups. Another cohort consisting of 402 patients with mono-lesion was used as control cohort. Results: No difference of age of onset was found between 32 patients and 403 patients with mono lesion (60.5 versus 60 years). Male had relatively lower incidence of multiple lung lesions (RR:0.46,95%CI: 0.20-0.93, P = 0.04). Eight patients were classified as “Genomic related” by presenting same mutation in driver or tumor suppressor genes. Six of eight patients were characterized to carry EGFR L858R, in addition, two patients presented co-mutation of RB1(c.1814+1G > T, p.E48Kfs*18) and TP53 mutations (p.H193R, p.R249S). Another two patients carried EGFR 19 Deletion. Two lesions from one patient with predefined diagnosis of intra-pulmonary metastasis showed biallelic loss of function mutations in same loci of NF1 gene (p.S2311*/ p.Q1360*) together with same KRAS mutation (p.G13C). Radiologically, no same lobe as well as left-right preference were revealed between “Genomic related” and “Genomic unrelated” groups. Histologically, there was no enrichment of patients with same histology subtype in “genomic related” group, verse visa. While, patients in “genomic related” group had higher ages at initial diagnosis (median age 69.5 vs 56.5 years, P = 0.04). Conclusions: Comprehensive genomic profiling should be applied to clinics distinguishing the nature of multiple lung lesion irrespective of radiological and histological diagnosis. [Table: see text]

ENAMEL RENAL SYNDROME: A NOVEL HOMOZYGOUS FAM20A FOUNDER MUTATION IN 5 NEW BRAZILIAN FAMILIES

Objective To investigate mutations in FAM20A of 11 unreported patients with ERS from 5 different Brazilian families. Study Design Clinical examination, imaging, renal ultrasonography, laboratory tests and DNA sequencing were performed in 11 patients with ERS. Results The patients' ages ranged from 6 to 25 years old, and the presence of hypoplastic amelogenesis imperfecta, microdontia, spaced teeth, intrapulpal calcification, impacted posterior teeth with hyperplastic pericoronal follicle, gingival fibromatosis, ectopic calcifications on gingival and pericoronal tissues, and nephrocalcinosis were common findings to all patients. Only 4 patients showed abnormal results in laboratory tests (vitamin D, parathyroid hormone, phosphate, calcium). Intellectual disability and renal cysts were present in 2 patients each. Biallelic loss of function mutations in FAM20A gene, characterized by 1 base pair deletion in exon 11 (c.1447 delG) and resulting in a premature stop codon at p.GLU483 LYSfsX24 were detected in all patients strongly suggesting a founder effect. Conclusions Our results reinforce the distinct orofacial features of ERS, which are the clue for kidney examination and genetic testing. Here we report the largest series of patients with ERS of the same population, and describe, for the first time, a founder mutation for FAM20A gene. FAPEMIG, FAPESP, CAPES.

P.380: Bi-allelic loss of function mutations in SYT2 cause a congenital onset severe presynaptic myasthenic syndrome

Synaptotagmins are integral membrane proteins of the synaptic vesicles that function as calcium sensors and regulate neurotransmitter release at the presynaptic nerve. Synaptotagmin II, encoded by SYT2, is the major isoform expressed at the neuromuscular junction. Syt2 deficient mice are known to develop a lethal impairment in synaptic transmission with a reduction in evoked release of neurotransmitters at the neuromuscular junction, manifesting with progressive motor degeneration. Recently dominant missense mutations in SYT2 have been reported as a rare cause of distal motor neuropathy and myasthenic syndrome, clinically manifesting as a relatively stable or slowly progressive, distal weakness of variable expressivity with presynaptic NMJ impairment, responsive to 3,4 diaminopyridine treatment in some patients. While the exact pathogenic mechanism of these dominantly-acting SYT2 missense mutations remains largely unknown, they all impact the C2B calcium-binding domain and are thought to have a dominant-negative effect on synaptic vesicle exocytosis. Here we report four patients, of three independent families, with bi-allelic loss-of-function mutations in SYT2, clinically manifesting with a remarkably consistent phenotype of severe congenital-onset hypotonia and weakness, with electrodiagnostic findings consistent with a presynaptic congenital myasthenic syndrome (CMS). This case series further establishes SYT2 as a CMS-disease gene and expands its clinical and genetic spectrum to include recessive loss-of-function mutations, manifesting as a severe congenital-onset presynaptic CMS with potential treatment implications, thus warranting an early genetic diagnosis.

Abstract 3480: TMEM30A loss-of-function mutations drive lymphomagenesis and confer therapeutically exploitable vulnerability in B-cell lymphoma

Abstract Diffuse large B-cell lymphoma (DLBCL) is the most common lymphoma subtype worldwide, accounting for 40% of all non-Hodgkin lymphomas. DLBCL presents as an aggressive disease requiring immediate treatment. Although significant improvement in outcome has been achieved, ~40% of patients still experience treatment failure. Here, we characterized the recurrent genetic alterations and transcriptomic signatures in diagnostic biopsies from a population registry-based cohort of 347 patients with de novo DLBCL uniformly treated with R-CHOP. This analysis revealed bi-allelic loss of function mutations of TMEM30A that were associated with favorable treatment outcome. TMEM30A is a chaperone protein, involved in maintaining the asymmetric distribution of phosphatidylethanolamine and phosphatidylserine, an integral component of the plasma membrane and “eat-me” signal recognized by macrophages. Using TMEM30A knockout systems by CRISPR genome editing techniques, we have functionally characterized this loss-of-function mutation in representative human and mouse DLBCL cell line models. We have discovered that TMEM30A loss is associated with increased B-cell signaling following antigen stimulation, including a two-fold increase in the diffusion rate of B-cell receptor (BCR) clustering, using high resolution Single Particle Tracking (SPT) technology. In addition, we have measured three-fold increase in chemotherapeutic drug accumulation in both knockout cell lines and randomly selected patient biopsies with TMEM30A biallelic loss. This observation was validated in a xenograft mouse model, which presented improved survival and limited tumor growth following vincristine treatment in mice injected with TMEM30A null DLBCL cell lines compared with native cell lines. This phenotype explains the improved prognosis observed in DLBCL patients following R-CHOP treatment. Furthermore, we have observed over two fold higher numbers of tumor-associated macrophages in B-cell lymphoma syngeneic mouse models with Tmem30a loss-of-function, prior to any form of treatment, suggesting the existence of “hot” and primed tumors. Our data highlight a multi-faceted role for TMEM30A and plasma membrane physiology in B-cell lymphomagenesis, and characterize intrinsic and extrinsic vulnerabilities of cancer cells that can be therapeutically exploited. Characterization of these mechanisms will address a missing link in the cancer field as related insights in lymphoma will outline therapeutic approaches that can be extended to cancer therapy in general. Citation Format: Shannon Healy, Daisuke Ennishi, Ali Bashashati, Saeed Saberi, Christoffer Hother, Anja Mottok, Fong Chun Chan, Lauren Chong, Robert Kridel, Merrill Boyle, Barbara Meissner, Tomohiro Aoki, Katsuyoshi Takata, Bruce W. Woolcock, Elena Vigano, Libin Abraham, Michael Gold, Adele Telenius, Pedro Farinha, Graham Slack, Susana Ben-Neriah, Daniel Lai, Allen W. Zhang, Sohrab Salehi, Hennady P. Shulha, Derek S. Chiu, Sara Mostafavi, Alina S. Gerrie, Diego Villa, Laurie H. Sehn, Kerry J. J. Savage, Andrew J. J. Mungall, Andrew P. Weng, Marcel Bally, Ryan D. Morin, Gabriela V. Cohen Freue, Joseph M. Connors, Marco A. Marra, Sohrab P. Shah, Randy D. Gascoyne1, David W. Scott, Christian Steidl, Ulrich Steidl. TMEM30A loss-of-function mutations drive lymphomagenesis and confer therapeutically exploitable vulnerability in B-cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3480.

Clinical, biochemical and genetic spectrum of 70 patients with ACAD9 deficiency: is riboflavin supplementation effective?

BackgroundMitochondrial acyl-CoA dehydrogenase family member 9 (ACAD9) is essential for the assembly of mitochondrial respiratory chain complex I. Disease causing biallelic variants in ACAD9 have been reported in individuals presenting with lactic acidosis and cardiomyopathy.ResultsWe describe the genetic, clinical and biochemical findings in a cohort of 70 patients, of whom 29 previously unpublished. We found 34 known and 18 previously unreported variants in ACAD9. No patients harbored biallelic loss of function mutations, indicating that this combination is unlikely to be compatible with life. Causal pathogenic variants were distributed throughout the entire gene, and there was no obvious genotype-phenotype correlation.Most of the patients presented in the first year of life. For this subgroup the survival was poor (50% not surviving the first 2 years) comparing to patients with a later presentation (more than 90% surviving 10 years). The most common clinical findings were cardiomyopathy (85%), muscular weakness (75%) and exercise intolerance (72%). Interestingly, severe intellectual deficits were only reported in one patient and severe developmental delays in four patients. More than 70% of the patients were able to perform the same activities of daily living when compared to peers.ConclusionsOur data show that riboflavin treatment improves complex I activity in the majority of patient-derived fibroblasts tested. This effect was also reported for most of the treated patients and is mirrored in the survival data. In the patient group with disease-onset below 1 year of age, we observed a statistically-significant better survival for patients treated with riboflavin.

Phenotypic characterization of KCTD3‐related developmental epileptic encephalopathy

The association between KCTD3 gene and neurogenetic disorders has only been published recently. In this report, we describe the clinical phenotype associated with 2 pathogenic variants in KCTD3 gene. Seven individuals (including one set of monozygotic twin) from 4 consanguineous families presented with developmental epileptic encephalopathy, global developmental delay, central hypotonia, progressive peripheral hypertonia, and variable dysmorphic facial features. Posterior fossa abnormalities (ranging from Dandy-Walker malformation to isolated hypoplasia of the cerebellar vermis) were consistently observed in addition to other variable neuroradiological abnormalities such as hydrocephalus and abnormal brain myelination. One patient also had a multicystic kidney. Whole exome sequencing revealed 2 probably pathogenic homozygous variants in KCTD3 gene that fully segregated with the disease. KCTD3 gene belongs to a family of accessory subunits that regulate the biophysical properties of ion channels, and is highly expressed in the kidney and brain. In this largest series to date on KCTD3-mutated patients, we show that biallelic loss of function mutations in KCTD3 lead to a consistent phenotype of developmental epileptic encephalopathy and abnormal cerebellum on brain imaging.