Biallelic Mutations in TBCD, Encoding the Tubulin Folding Cofactor D, Perturb Microtubule Dynamics and Cause Early-Onset Encephalopathy

Am J Hum Genet. 2016 Oct 6;99(4):962-973. doi: 10.1016/j.ajhg.2016.08.003.

Elisabetta Flex ¹, Marcello Niceta ², Serena Cecchetti ³, Isabelle Thiffault ⁴, Margaret G Au ⁵, Alessandro Capuano ², Emanuela Piermarini ², Anna A Ivanova ⁶, Joshua W Francis ⁶, Giovanni Chillemi ⁷, Balasubramanian Chandramouli ⁸, Giovanna Carpentieri ⁹, Charlotte A Haaxma ¹⁰, Andrea Ciolfi ¹¹, Simone Pizzi ², Ganka V Douglas ¹², Kara Levine ¹², Antonella Sferra ², Maria Lisa Dentici ², Rolph R Pfundt ¹⁰, Jean-Baptiste Le Pichon ¹³, Emily Farrow ¹⁴, Frank Baas ¹⁵, Fiorella Piemonte ², Bruno Dallapiccola ², John M Graham Jr ⁵, Carol J Saunders ⁴, Enrico Bertini ², Richard A Kahn ⁶, David A Koolen ¹⁶, Marco Tartaglia ¹⁷

Affiliations

1 Department of Hematology, Oncology and Molecular Medicine, Istituto Superiore di Sanità, Rome 00161, Italy.
2 Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, Rome 00146, Italy.
3 Department of Cell Biology and Neurosciences, Istituto Superiore di Sanità, Rome 00161, Italy.
4 Center for Pediatric Genomic Medicine, Children's Mercy Hospital, Kansas City, MO 64108, USA; Department of Pathology and Laboratory Medicine, Children's Mercy Hospital, Kansas City, MO 64108, USA; University of Missouri-Kansas City School of Medicine, Kansas City, MO 64108, USA.
5 Department of Pediatrics, Medical Genetics, Cedars-Sinai Medical Center, Los Angeles, CA 90048, USA.
6 Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322, USA.
7 CINECA, SCAI-SuperComputing Applications and Innovation Department, Rome 00185, Italy.
8 Scuola Normale Superiore, 56126 Pisa, Italy.
9 Department of Hematology, Oncology and Molecular Medicine, Istituto Superiore di Sanità, Rome 00161, Italy; Dipartimento di Medicina Sperimentale, Sapienza Università di Roma, Rome 00161, Italy.
10 Department of Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen 1105, the Netherlands.
11 Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, Rome 00146, Italy; Centro di Ricerca per gli alimenti e la nutrizione, CREA, Rome 00178, Italy.
12 GeneDx, Gaithersburg, MD 20877, USA.
13 Department of Pediatrics, Children's Mercy Hospitals, Kansas City, MO 64108, USA.
14 Center for Pediatric Genomic Medicine, Children's Mercy Hospital, Kansas City, MO 64108, USA.
15 Department of Genome Analysis, Academic Medical Center, Amsterdam 1105, the Netherlands.
16 Department of Human Genetics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen 1105, the Netherlands.
17 Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, Rome 00146, Italy. Electronic address: marco.tartaglia@opbg.net.

PMID: 27666370 DOI: 10.1016/j.ajhg.2016.08.003

Abstract

Microtubules are dynamic cytoskeletal elements coordinating and supporting a variety of neuronal processes, including cell division, migration, polarity, intracellular trafficking, and signal transduction. Mutations in genes encoding tubulins and microtubule-associated proteins are known to cause neurodevelopmental and neurodegenerative disorders. Growing evidence suggests that altered microtubule dynamics may also underlie or contribute to neurodevelopmental disorders and neurodegeneration. We report that biallelic mutations in TBCD, encoding one of the five co-chaperones required for assembly and disassembly of the αβ-tubulin heterodimer, the structural unit of microtubules, cause a disease with neurodevelopmental and neurodegenerative features characterized by early-onset cortical atrophy, secondary hypomyelination, microcephaly, thin corpus callosum, developmental delay, intellectual disability, seizures, optic atrophy, and spastic quadriplegia. Molecular dynamics simulations predicted long-range and/or local structural perturbations associated with the disease-causing mutations. Biochemical analyses documented variably reduced levels of TBCD, indicating relative instability of mutant proteins, and defective β-tubulin binding in a subset of the tested mutants. Reduced or defective TBCD function resulted in decreased soluble α/β-tubulin levels and accelerated microtubule polymerization in fibroblasts from affected subjects, demonstrating an overall shift toward a more rapidly growing and stable microtubule population. These cells displayed an aberrant mitotic spindle with disorganized, tangle-shaped microtubules and reduced aster formation, which however did not alter appreciably the rate of cell proliferation. Our findings establish that defective TBCD function underlies a recognizable encephalopathy and drives accelerated microtubule polymerization and enhanced microtubule stability, underscoring an additional cause of altered microtubule dynamics with impact on neuronal function and survival in the developing brain.

Name
Email *

	Sorry, but the email address you supplied was invalid.