@article {814, title = {Mutations in MYLPF Cause a Novel Segmental Amyoplasia that Manifests as Distal Arthrogryposis.}, journal = {Am J Hum Genet}, volume = {107}, year = {2020}, month = {2020 08 06}, pages = {293-310}, abstract = {

We identified ten persons in six consanguineous families with distal arthrogryposis (DA) who had congenital contractures, scoliosis, and short stature. Exome sequencing revealed that each affected person was homozygous for one of two different rare variants (c.470G>T [p.Cys157Phe] or c.469T>C [p.Cys157Arg]) affecting the same residue of myosin light chain, phosphorylatable, fast skeletal muscle (MYLPF). In a seventh family, a c.487G>A (p.Gly163Ser) variant in MYLPF arose de novo in a father, who transmitted it to his son. In an eighth family comprised of seven individuals with dominantly inherited DA, a c.98C>T (p.Ala33Val) variant segregated in all four persons tested. Variants in MYLPF underlie both dominant and recessively inherited DA. Mylpf protein models suggest that the residues associated with dominant DA interact with myosin whereas the residues altered in families with recessive DA only indirectly impair this interaction. Pathological and histological exam of a foot amputated from an affected child revealed complete absence of skeletal muscle (i.e., segmental amyoplasia). To investigate the mechanism for this finding, we generated an animal model for partial MYLPF impairment by knocking out zebrafish mylpfa. The mylpfa mutant had reduced trunk contractile force and complete pectoral fin paralysis, demonstrating that mylpf impairment most severely affects limb movement. mylpfa mutant muscle weakness was most pronounced in an appendicular muscle and was explained by reduced myosin activity and fiber degeneration. Collectively, our findings demonstrate that partial loss of MYLPF function can lead to congenital contractures, likely as a result of degeneration of skeletal muscle in the distal limb.

}, keywords = {Adolescent, Amino Acid Sequence, Animals, Arthrogryposis, Child, Contracture, Extremities, Female, Humans, Male, Muscle, Skeletal, Musculoskeletal Abnormalities, Mutation, Myosin Light Chains, Myosins, Pedigree, Young Adult, Zebrafish}, issn = {1537-6605}, doi = {10.1016/j.ajhg.2020.06.014}, author = {Chong, Jessica X and Talbot, Jared C and Teets, Emily M and Previs, Samantha and Martin, Brit L and Shively, Kathryn M and Marvin, Colby T and Aylsworth, Arthur S and Saadeh-Haddad, Reem and Schatz, Ulrich A and Inzana, Francesca and Ben-Omran, Tawfeg and Almusafri, Fatima and Al-Mulla, Mariam and Buckingham, Kati J and Harel, Tamar and Mor-Shaked, Hagar and Radhakrishnan, Periyasamy and Girisha, Katta M and Nayak, Shalini S and Shukla, Anju and Dieterich, Klaus and Faure, Julien and Rendu, John and Capri, Yline and Latypova, X{\'e}nia and Nickerson, Deborah A and Warshaw, David M and Janssen, Paul M L and Amacher, Sharon L and Bamshad, Michael J} } @article {338, title = {Mutations in EBF3 Disturb Transcriptional Profiles and Cause Intellectual Disability, Ataxia, and Facial Dysmorphism.}, journal = {Am J Hum Genet}, volume = {100}, year = {2017}, month = {2017 Jan 05}, pages = {117-127}, abstract = {

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.

}, keywords = {Adolescent, Adult, Amino Acid Substitution, Ataxia, Child, Child, Preschool, Chromatin, Cyclin-Dependent Kinase Inhibitor p21, Developmental Disabilities, Exome, Face, Female, Gene Expression Regulation, Genes, Reporter, HEK293 Cells, Humans, Intellectual Disability, Language Development Disorders, Male, Models, Molecular, Mosaicism, Mutation, Neurodevelopmental Disorders, Protein Transport, Syndrome, Transcription Factors, Transcription, Genetic}, issn = {1537-6605}, doi = {10.1016/j.ajhg.2016.11.012}, author = {Harms, Frederike Leonie and Girisha, Katta M and Hardigan, Andrew A and Kort{\"u}m, Fanny and Shukla, Anju and Alawi, Malik and Dalal, Ashwin and Brady, Lauren and Tarnopolsky, Mark and Bird, Lynne M and Ceulemans, Sophia and Bebin, Martina and Bowling, Kevin M and Hiatt, Susan M and Lose, Edward J and Primiano, Michelle and Chung, Wendy K and Juusola, Jane and Akdemir, Zeynep C and Bainbridge, Matthew and Charng, Wu-Lin and Drummond-Borg, Margaret and Eldomery, Mohammad K and El-Hattab, Ayman W and Saleh, Mohammed A M and B{\'e}zieau, St{\'e}phane and Cogn{\'e}, Benjamin and Isidor, Bertrand and K{\"u}ry, S{\'e}bastien and Lupski, James R and Myers, Richard M and Cooper, Gregory M and Kutsche, Kerstin} } @article {58, title = {Association of MTOR Mutations With Developmental Brain Disorders, Including Megalencephaly, Focal Cortical Dysplasia, and Pigmentary Mosaicism.}, journal = {JAMA Neurol}, volume = {73}, year = {2016}, month = {2016 07 01}, pages = {836-845}, abstract = {

IMPORTANCE: Focal cortical dysplasia (FCD), hemimegalencephaly, and megalencephaly constitute a spectrum of malformations of cortical development with shared neuropathologic features. These disorders are associated with significant childhood morbidity and mortality.

OBJECTIVE: To identify the underlying molecular cause of FCD, hemimegalencephaly, and diffuse megalencephaly.

DESIGN, SETTING, AND PARTICIPANTS: Patients with FCD, hemimegalencephaly, or megalencephaly (mean age, 11.7 years; range, 2-32 years) were recruited from Pediatric Hospital A. Meyer, the University of Hong Kong, and Seattle Children{\textquoteright}s Research Institute from June 2012 to June 2014. Whole-exome sequencing (WES) was performed on 8 children with FCD or hemimegalencephaly using standard-depth (50-60X) sequencing in peripheral samples (blood, saliva, or skin) from the affected child and their parents and deep (150-180X) sequencing in affected brain tissue. Targeted sequencing and WES were used to screen 93 children with molecularly unexplained diffuse or focal brain overgrowth. Histopathologic and functional assays of phosphatidylinositol 3-kinase-AKT (serine/threonine kinase)-mammalian target of rapamycin (mTOR) pathway activity in resected brain tissue and cultured neurons were performed to validate mutations.

MAIN OUTCOMES AND MEASURES: Whole-exome sequencing and targeted sequencing identified variants associated with this spectrum of developmental brain disorders.

RESULTS: Low-level mosaic mutations of MTOR were identified in brain tissue in 4 children with FCD type 2a with alternative allele fractions ranging from 0.012 to 0.086. Intermediate-level mosaic mutation of MTOR (p.Thr1977Ile) was also identified in 3 unrelated children with diffuse megalencephaly and pigmentary mosaicism in skin. Finally, a constitutional de novo mutation of MTOR (p.Glu1799Lys) was identified in 3 unrelated children with diffuse megalencephaly and intellectual disability. Molecular and functional analysis in 2 children with FCD2a from whom multiple affected brain tissue samples were available revealed a mutation gradient with an epicenter in the most epileptogenic area. When expressed in cultured neurons, all MTOR mutations identified here drive constitutive activation of mTOR complex 1 and enlarged neuronal size.

CONCLUSIONS AND RELEVANCE: In this study, mutations of MTOR were associated with a spectrum of brain overgrowth phenotypes extending from FCD type 2a to diffuse megalencephaly, distinguished by different mutations and levels of mosaicism. These mutations may be sufficient to cause cellular hypertrophy in cultured neurons and may provide a demonstration of the pattern of mosaicism in brain and substantiate the link between mosaic mutations of MTOR and pigmentary mosaicism in skin.

}, keywords = {Adolescent, Adult, Amino Acids, Animals, Cells, Cultured, Cerebral Cortex, Child, Child, Preschool, Developmental Disabilities, Embryo, Mammalian, Female, Gene Expression Regulation, Genetic Association Studies, Humans, Intercellular Signaling Peptides and Proteins, Male, Malformations of Cortical Development, Mechanistic Target of Rapamycin Complex 1, Megalencephaly, Mosaicism, Multiprotein Complexes, Mutation, Nerve Tissue Proteins, Neurons, Rats, Retrospective Studies, TOR Serine-Threonine Kinases, Young Adult}, issn = {2168-6157}, doi = {10.1001/jamaneurol.2016.0363}, author = {Mirzaa, Ghayda M and Campbell, Catarina D and Solovieff, Nadia and Goold, Carleton and Jansen, Laura A and Menon, Suchithra and Timms, Andrew E and Conti, Valerio and Biag, Jonathan D and Adams, Carissa and Boyle, Evan August and Collins, Sarah and Ishak, Gisele and Poliachik, Sandra and Girisha, Katta M and Yeung, Kit San and Chung, Brian Hon Yin and Rahikkala, Elisa and Gunter, Sonya A and McDaniel, Sharon S and Macmurdo, Colleen Forsyth and Bernstein, Jonathan A and Martin, Beth and Leary, Rebecca and Mahan, Scott and Liu, Shanming and Weaver, Molly and Doerschner, Michael and Jhangiani, Shalini and Muzny, Donna M and Boerwinkle, Eric and Gibbs, Richard A and Lupski, James R and Shendure, Jay and Saneto, Russell P and Novotny, Edward J and Wilson, Christopher J and Sellers, William R and Morrissey, Michael and Hevner, Robert F and Ojemann, Jeffrey G and Guerrini, Renzo and Murphy, Leon O and Winckler, Wendy and Dobyns, William B} }