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ABHD16A (abhydrolase domain-containing protein 16A, phospholipase) encodes the major phosphatidylserine (PS) lipase in the brain. PS lipase synthesizes lysophosphatidylserine, an important signaling lipid that functions in the mammalian central nervous system. ABHD16A has not yet been associated with a human disease. In this report, we present a cohort of 11 affected individuals from six unrelated families with a complicated form of hereditary spastic paraplegia (HSP) who carry bi-allelic deleterious variants in ABHD16A. Affected individuals present with a similar phenotype consisting of global developmental delay/intellectual disability, progressive spasticity affecting the upper and lower limbs, and corpus callosum and white matter anomalies. Immunoblot analysis on extracts from fibroblasts from four affected individuals demonstrated little to no ABHD16A protein levels compared to controls. Our findings add ABHD16A to the growing list of lipid genes in which dysregulation can cause complicated forms of HSP and begin to describe the molecular etiology of this condition., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.)

Reports of patients with concomitant diagnoses of two inherited genetic disorders, sometimes referred to as "double trouble," have appeared intermittently in the medical literature. We report eight additional cases with dual diagnoses of two genetic conditions. All cases had a phenotype atypical for their primary diagnosis, leading to the search for a second genetic diagnosis. These cases highlight the importance of the history, physical examination and continued work-up if the phenotype of the patient falls drastically outside what has been reported with their primary diagnosis. Some of the diagnoses of the patients presented here (e.g., Myotonic Dystrophy Type 1, fascioscapulohumeral muscular dystrophy) would not have been identified by genetic testing done on a next generation sequencing backbone (e.g., panel or exome sequencing). When the clinical picture is atypical or more severe than expected the possibility of a dual diagnosis (double trouble) should be considered. Identification of a second genetic condition can impact management and genetic counseling., (© 2020 Wiley Periodicals LLC.)

While >300 disease-causing variants have been identified in the mitochondrial DNA (mtDNA) polymerase γ, no mitochondrial phenotypes have been associated with POLRMT, the RNA polymerase responsible for transcription of the mitochondrial genome. Here, we characterise the clinical and molecular nature of POLRMT variants in eight individuals from seven unrelated families. Patients present with global developmental delay, hypotonia, short stature, and speech/intellectual disability in childhood; one subject displayed an indolent progressive external ophthalmoplegia phenotype. Massive parallel sequencing of all subjects identifies recessive and dominant variants in the POLRMT gene. Patient fibroblasts have a defect in mitochondrial mRNA synthesis, but no mtDNA deletions or copy number abnormalities. The in vitro characterisation of the recombinant POLRMT mutants reveals variable, but deleterious effects on mitochondrial transcription. Together, our in vivo and in vitro functional studies of POLRMT variants establish defective mitochondrial transcription as an important disease mechanism.

Mitochondrial dynamics, including mitochondrial division, fusion and transport, are integral parts of mitochondrial and cellular function. DNM1L encodes dynamin-related protein 1 (Drp1), a member of the dynamin-related protein family that is required for mitochondrial division. Several de novo mutations in DNM1L are associated with a range of disease states. Here we report the identification of five patients with pathogenic or likely pathogenic variants of DNM1L, including two novel variants. Interestingly, all of the positions identified in these Drp1 variants are fully conserved among all members of the dynamin-related protein family that are involved in membrane division and organelle division events. This work builds upon and expands the clinical spectrum associated with Drp1 variants in patients and their impact on mitochondrial division in model cells.

Background: Ogden syndrome is a rare X-linked disorder caused by pathogenic variants in the NAA10 gene. This syndrome, reported in just over 20 children, has been associated with dysmorphic features, failure to thrive, developmental impairments, hypotonia, and cardiac arrhythmias., Patient Description: We describe a 14-year-old girl who presented in infancy with hypotonia, global developmental delay, and dysmorphic features. She later developed autism spectrum disorder, epileptic encephalopathy, extrapyramidal signs, early morning lethargy with hypersomnolence, and hypertension with left ventricular hypertrophy. Magnetic resonance imaging showed a thin corpus callosum and progressive white matter loss. Whole exome sequencing identified a de novo pathogenic variant in the NAA10 gene (c.247C>T, p.R83C). Much of her early presentation was in keeping with what has been previously described with Ogden syndrome., Conclusions: We have identified additional evolving neurological impairments in this, to date, oldest documented girl with Ogden syndrome. We recommend screening patients with Ogden syndrome for these newly identified features of early life trajectories to guide management., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Background: We aimed for a comprehensive delineation of genetic, functional and phenotypic aspects of GRIN2B encephalopathy and explored potential prospects of personalised medicine., Methods: Data of 48 individuals with de novo GRIN2B variants were collected from several diagnostic and research cohorts, as well as from 43 patients from the literature. Functional consequences and response to memantine treatment were investigated in vitro and eventually translated into patient care., Results: Overall, de novo variants in 86 patients were classified as pathogenic/likely pathogenic. Patients presented with neurodevelopmental disorders and a spectrum of hypotonia, movement disorder, cortical visual impairment, cerebral volume loss and epilepsy. Six patients presented with a consistent malformation of cortical development (MCD) intermediate between tubulinopathies and polymicrogyria. Missense variants cluster in transmembrane segments and ligand-binding sites. Functional consequences of variants were diverse, revealing various potential gain-of-function and loss-of-function mechanisms and a retained sensitivity to the use-dependent blocker memantine. However, an objectifiable beneficial treatment response in the respective patients still remains to be demonstrated., Conclusions: In addition to previously known features of intellectual disability, epilepsy and autism, we found evidence that GRIN2B encephalopathy is also frequently associated with movement disorder, cortical visual impairment and MCD revealing novel phenotypic consequences of channelopathies., Competing Interests: Competing interests: SFT is a consultant of Janssen Pharmaceuticals, Inc., Pfizer Inc., Boehringer Ingelheim Pharma GmbH & Co. KG, and co-founder of NeurOp Inc., (© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.)

Recent research has suggested that transmembrane protein 65 (TMEM65) is localized within the inner mitochondrial membrane. Little else is known about its function. In this study we investigated the location and function of TMEM65. Further, we report the functional consequences of a novel homozygous splice variant (c.472+1G>A) in the TMEM65 gene in a patient with mitochondrial encephalomyopathy. Here we investigated the location of TMEM65 by immunofluorescence staining of the protein and by immunoblotting of the isolated mitochondrial fractions in healthy fibroblasts and those from the patient. To study the function of TMEM65 we knocked down mRNA using TMEM65-specific siRNA, and measured mitochondrial function by enzymology, protein abundance and oxygen consumption rate in fibroblasts. Subcellular fractionation confirmed that the TMEM65 protein was present in the inner mitochondrial membrane. Knocking down TMEM65 expression in dermal fibroblasts severely affected mitochondrial content and respiration rate. Further evidence for the essential role of TMEM65 in mitochondrial function came from the demonstration of severe cellular and clinical consequences resulting from the novel TMEM65 gene mutation. In conclusion, these findings suggest that TMEM65, an inner mitochondrial membrane protein, plays a significant role in mitochondrial respiratory chain function. We also provide the first evidence that a mutation in the TMEM65 gene results in mitochondrial dysfunction and a severe mitochondrial encephalomyopathy phenotype.

From a GeneMatcher-enabled international collaboration, we identified ten individuals affected by intellectual disability, speech delay, ataxia, and facial dysmorphism and carrying a deleterious EBF3 variant detected by whole-exome sequencing. One 9-bp duplication and one splice-site, five missense, and two nonsense variants in EBF3 were found; the mutations occurred de novo in eight individuals, and the missense variant c.625C>T (p.Arg209Trp) was inherited by two affected siblings from their healthy mother, who is mosaic. EBF3 belongs to the early B cell factor family (also known as Olf, COE, or O/E) and is a transcription factor involved in neuronal differentiation and maturation. Structural assessment predicted that the five amino acid substitutions have damaging effects on DNA binding of EBF3. Transient expression of EBF3 mutant proteins in HEK293T cells revealed mislocalization of all but one mutant in the cytoplasm, as well as nuclear localization. By transactivation assays, all EBF3 mutants showed significantly reduced or no ability to activate transcription of the reporter gene CDKN1A, and in situ subcellular fractionation experiments demonstrated that EBF3 mutant proteins were less tightly associated with chromatin. Finally, in RNA-seq and ChIP-seq experiments, EBF3 acted as a transcriptional regulator, and mutant EBF3 had reduced genome-wide DNA binding and gene-regulatory activity. Our findings demonstrate that variants disrupting EBF3-mediated transcriptional regulation cause intellectual disability and developmental delay and are present in ∼0.1% of individuals with unexplained neurodevelopmental disorders., (Copyright © 2017 American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.)

We describe here two novel mitochondrial mutations associated with a complex mitochondrial encephalopathy. An A to G transition at position 7495 (MT-TS1 (MT-tRNSer(UCN))) was identified at 83% heteroplasmy in the muscle of a four year old female with ptosis, hypotonia, seizures, and dilated cardiomyopathy (Case 1). A homoplasmic C to T transition at position 5577 (MT-TW (MT-tRNATrp)) was found in a twenty-four year old woman with exercise intolerance, mild muscle weakness, hearing loss, seizures, and cognitive decline (Case 2). The phenotypic information provided here will assist in phenotype-genotype correlations should additional patients be reported in the future. The mutations can be added to the database of mitochondrial DNA variations in conserved regions which result in clinically diverse phenotypes with the shared markers of mitochondrial disease., (Copyright © 2016 Elsevier B.V. and Mitochondria Research Society. All rights reserved.)