Biallelic Mutations in TBCD, Encoding the Tubulin Folding Cofactor D, Perturb Microtubule Dynamics and Cause Early-Onset Encephalopathy.
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.
Department of Hematology, Oncology and Molecular Medicine, Istituto Superiore di Sanità, Rome 00161, Italy.
Elisabetta
E
Flex
Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, Rome 00146, Italy.
Marcello
M
Niceta
Department of Cell Biology and Neurosciences, Istituto Superiore di Sanità, Rome 00161, Italy.
Serena
S
Cecchetti
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.
Isabelle
I
Thiffault
Department of Pediatrics, Medical Genetics, Cedars-Sinai Medical Center, Los Angeles, CA 90048, USA.
Margaret G
MG
Au
Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, Rome 00146, Italy.
Alessandro
A
Capuano
Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, Rome 00146, Italy.
Emanuela
E
Piermarini
Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322, USA.
Anna A
AA
Ivanova
Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322, USA.
Joshua W
JW
Francis
CINECA, SCAI-SuperComputing Applications and Innovation Department, Rome 00185, Italy.
Giovanni
G
Chillemi
Scuola Normale Superiore, 56126 Pisa, Italy.
Balasubramanian
B
Chandramouli
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.
Giovanna
G
Carpentieri
Department of Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen 1105, the Netherlands.
Charlotte A
CA
Haaxma
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.
Andrea
A
Ciolfi
Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, Rome 00146, Italy.
Simone
S
Pizzi
GeneDx, Gaithersburg, MD 20877, USA.
Ganka V
GV
Douglas
GeneDx, Gaithersburg, MD 20877, USA.
Kara
K
Levine
Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, Rome 00146, Italy.
Antonella
A
Sferra
Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, Rome 00146, Italy.
Maria Lisa
ML
Dentici
Department of Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen 1105, the Netherlands.
Rolph R
RR
Pfundt
Department of Pediatrics, Children's Mercy Hospitals, Kansas City, MO 64108, USA.
Jean-Baptiste
JB
Le Pichon
Center for Pediatric Genomic Medicine, Children's Mercy Hospital, Kansas City, MO 64108, USA.
Emily
E
Farrow
Department of Genome Analysis, Academic Medical Center, Amsterdam 1105, the Netherlands.
Frank
F
Baas
Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, Rome 00146, Italy.
Fiorella
F
Piemonte
Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, Rome 00146, Italy.
Bruno
B
Dallapiccola
Department of Pediatrics, Medical Genetics, Cedars-Sinai Medical Center, Los Angeles, CA 90048, USA.
John M
JM
Graham
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.
Carol J
CJ
Saunders
Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, Rome 00146, Italy.
Enrico
E
Bertini
Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322, USA.
Richard A
RA
Kahn
Department of Human Genetics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen 1105, the Netherlands.
David A
DA
Koolen
Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, Rome 00146, Italy. Electronic address: marco.tartaglia@opbg.net.
Marco
M
Tartaglia
D000293:Adolescent; D017668:Age of Onset; D000483:Alleles; D001921:Brain / Q000378:metabolism / Q000473:pathology; D001927:Brain Diseases / Q000235:genetics* / Q000473:pathology; D049109:Cell Proliferation; D002675:Child, Preschool; D005260:Female; D005347:Fibroblasts; D006801:Humans; D007223:Infant; D008297:Male; D008869:Microtubule-Associated Proteins / Q000235:genetics* / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism* / Q000473:pathology; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D011485:Protein Binding; D017510:Protein Folding; D008941:Spindle Apparatus / Q000378:metabolism / Q000473:pathology; D014404:Tubulin / Q000737:chemistry / Q000378:metabolism*
D008869:Microtubule-Associated Proteins; D018832:Molecular Chaperones; C418662:TBCD protein, human; D014404:Tubulin
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