Two unique TUBB3 mutations cause both CFEOM3 and malformations of cortical development (original) (raw)
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Human Molecular Genetics, 2010
Gé né tique Chromosomique, AP-HP, hô pital Pitié -Salpé triè re, Mutations in the TUBB3 gene, encoding b-tubulin isotype III, were recently shown to be associated with various neurological syndromes which all have in common the ocular motility disorder, congenital fibrosis of the extraocular muscle type 3 (CFEOM3). Surprisingly and in contrast to previously described TUBA1A and TUBB2B phenotypes, no evidence of dysfunctional neuronal migration and cortical organization was reported. In our study, we report the discovery of six novel missense mutations in the TUBB3 gene, including one fetal case and one homozygous variation, in nine patients that all share cortical disorganization, axonal abnormalities associated with pontocerebellar hypoplasia, but with no ocular motility defects, CFEOM3. These new findings demonstrate that the spectrum of TUBB3-related phenotype is broader than previously described and includes malformations of cortical development (MCD) associated with neuronal migration and differentiation defects, axonal guidance and tract organization impairment. Complementary functional studies revealed that the mutated bIII-tubulin causing the MCD phenotype results in a reduction of heterodimer formation, yet produce correctly formed microtubules (MTs) in mammalian cells. Further to this, we investigated the properties of the MT network in patients' fibroblasts and revealed that MCD mutations can alter the resistance of MTs to depolymerization. Interestingly, this finding contrasts with the increased MT stability observed in the case of CFEOM3-related mutations. These results led us to hypothesize that either MT dynamics or their interactions with various MT-interacting proteins could be differently affected by TUBB3 variations, thus resulting in distinct alteration of downstream processes and therefore explaining the phenotypic diversity of the TUBB3-related spectrum. †
Human Molecular Genetics, 2010
Mutations in the TUBB3 gene, encoding b-tubulin isotype III, were recently shown to be associated with various neurological syndromes which all have in common the ocular motility disorder, congenital fibrosis of the extraocular muscle type 3 (CFEOM3). Surprisingly and in contrast to previously described TUBA1A and TUBB2B phenotypes, no evidence of dysfunctional neuronal migration and cortical organization was reported. In our study, we report the discovery of six novel missense mutations in the TUBB3 gene, including one fetal case and one homozygous variation, in nine patients that all share cortical disorganization, axonal abnormalities associated with pontocerebellar hypoplasia, but with no ocular motility defects, CFEOM3. These new findings demonstrate that the spectrum of TUBB3-related phenotype is broader than previously described and includes malformations of cortical development (MCD) associated with neuronal migration and differentiation defects, axonal guidance and tract organization impairment. Complementary functional studies revealed that the mutated bIII-tubulin causing the MCD phenotype results in a reduction of heterodimer formation, yet produce correctly formed microtubules (MTs) in mammalian cells. Further to this, we investigated the properties of the MT network in patients' fibroblasts and revealed that MCD mutations can alter the resistance of MTs to depolymerization. Interestingly, this finding contrasts with the increased MT stability observed in the case of CFEOM3-related mutations. These results led us to hypothesize that either MT dynamics or their interactions with various MT-interacting proteins could be differently affected by TUBB3 variations, thus resulting in distinct alteration of downstream processes and therefore explaining the phenotypic diversity of the TUBB3-related spectrum.
Tubulin genes and malformations of cortical development
European journal of medical genetics, 2018
A large number of genes encoding for tubulin proteins are expressed in the developing brain. Each is subject to specific spatial and temporal expression patterns. However, most are highly expressed in post-mitotic neurons during stages of neuronal migration and differentiation. The major tubulin subclasses (alpha- and beta-tubulin) share high sequence and structural homology. These globular proteins form heterodimers and subsequently co-assemble into microtubules. Microtubules are dynamic, cytoskeletal polymers which play key roles in cellular processes crucial for cortical development, including neuronal proliferation, migration and cortical laminar organisation. Mutations in seven genes encoding alpha-tubulin (TUBA1A), beta-tubulin (TUBB2A, TUBB2B, TUBB3, TUBB4A, TUBB) and gamma-tubulin (TUBG1) isoforms have been associated with a wide and overlapping range of brain malformations or "Tubulinopathies". The majority of cortical phenotypes include lissencephaly, polymicrogy...
Developmental Medicine & Child Neurology, 2014
The aim of this study was to determine the frequency of mutations in tubulin genes (TUBB2B, TUBA1A, and TUBB3) in patients with malformations of cortical development (MCDs) of unknown origin. METHOD In total, 79 out of 156 patients (41 males, 38 females; age range 8mo-55y (mean age 13y 3mo, SD 11y 2mo) with a neuroradiological diagnosis of MCDs were enrolled in the study. The 77 excluded patients were excluded for the following reasons: suspected or proven diagnosis of pre-or perinatal ischaemic insult (n=13); syndromic disease (n=10); congenital infection (n=14); pregnancy complicated by twin-to-twin transfusion syndrome (n=2); proven mutations in known genes (n=13); poor magnetic resonance imaging (MRI) quality, or lack of informed consent (n=25). A genetic analysis of the TUBA1A, TUBB2B and TUBB3 genes was carried out by direct sequencing of the coding regions of the relevant genes for each participant. Previously described patients with mutations in the TUBB2B and TUBA1A genes were reviewed; clinical and neuroradiological findings were compared and discussed. RESULTS Two novel heterozygous mutations were detected: a heterozygous mutation in exon 4 of the TUBA1A gene (c.1160C>T) in a 5-year-old female with microcephaly, severe intellectual disability, and absence of language, and a c.1080 _1084del CCTGAinsACATCTTC in exon 4 of the TUBB2B gene in a 31-year-old female with microcephaly, spastic tetraparesis, severe intellectual disability, and scoliosis. Different types of cortical abnormalities, cerebellar vermis hypoplasia, and optic nerve hypoplasia/atrophy were detected on MRI. Dysmorphisms of the basal ganglia and the hippocampi with abnormalities of the midline commissural structures were present in both cases. INTERPRETATION The consistent presence of hypoplastic and disorganized white matter tracts suggests that, in addition to defects in neuronal migration, disruption of axon growth and guidance is a peculiar feature of tubulin-related disorders.
Mutations in the β-Tubulin Gene TUBB5 Cause Microcephaly with Structural Brain Abnormalities
Cell Reports, 2012
The formation of the mammalian cortex requires the generation, migration, and differentiation of neurons. The vital role that the microtubule cytoskeleton plays in these cellular processes is reflected by the discovery that mutations in various tubulin isotypes cause different neurodevelopmental diseases, including lissencephaly (TUBA1A), polymicrogyria (TUBA1A, TUBB2B, TUBB3), and an ocular motility disorder (TUBB3). Here, we show that Tubb5 is expressed in neurogenic progenitors in the mouse and that its depletion in vivo perturbs the cell cycle of progenitors and alters the position of migrating neurons. We report the occurrence of three microcephalic patients with structural brain abnormalities harboring de novo mutations in TUBB5 (M299V, V353I, and E401K). These mutant proteins, which affect the chaperonedependent assembly of tubulin heterodimers in different ways, disrupt neurogenic division and/or migration in vivo. Our results provide insight into the functional repertoire of the tubulin gene family, specifically implicating TUBB5 in embryonic neurogenesis and microcephaly.
Investigative Ophthalmology & Visual Science, 2010
Orbital magnetic resonance imaging (MRI) was used to investigate the structural basis of motility abnormalities in congenital fibrosis of the extraocular muscles type 3 (CFEOM3), a disorder resulting from missense mutations in TUBB3, which encodes neuron-specific -tubulin isotype III. METHODS. Ophthalmic examinations in 13 volunteers from four CFEOM3 pedigrees and normal control subjects, were correlated with TUBB3 mutation and MRI findings that demonstrated extraocular muscle (EOM) size, location, contractility, and innervation. RESULTS. Volunteers included clinically affected and clinically unaffected carriers of R262C and D417N TUBB3 amino acid substitutions and one unaffected, mutation-negative family member. Subjects with CFEOM3 frequently had asymmetrical blepharoptosis, limited vertical duction, variable ophthalmoplegia, exotropia, and paradoxical abduction in infraduction. MRI demonstrated variable, asymmetrical levator palpebrae superioris and superior rectus EOM atrophy that correlated with blepharoptosis, deficient supraduction, and small orbital motor nerves. Additional EOMs exhibited variable hypoplasia that correlated with duction deficit, but the superior oblique muscle was spared. Ophthalmoplegia occurred only when the subarachnoid width of CN3 was Ͻ1.9 mm. A-pattern exotropia was frequent, correlating with apparent lateral rectus (LR) muscle misinnervation by CN3. Optic nerve (ON) cross sections were subnormal, but rectus pulley locations were normal. CONCLUSIONS. CFEOM3 caused by TUBB3 R262C and D417N amino acid substitutions features abnormalities of EOM innervation and function that correlate with subarachnoid CN3 hypoplasia, occasional abducens nerve hypoplasia, and subclinical ON From the
Nature Communications
De novo heterozygous missense variants in the γ-tubulin gene TUBG1 have been linked to human malformations of cortical development associated with intellectual disability and epilepsy. Here, we investigated through in-utero electroporation and in-vivo studies, how four of these variants affect cortical development. We show that TUBG1 mutants affect neuronal positioning, disrupting the locomotion of newborn neurons but without affecting progenitors' proliferation. We further demonstrate that pathogenic TUBG1 variants are linked to reduced microtubule dynamics but without major structural nor functional centrosome defects in subject-derived fibroblasts. Additionally, we developed a knock-in Tubg1 Y92C/+ mouse model and assessed consequences of the mutation. Although centrosomal positioning in bipolar neurons is correct, they fail to initiate locomotion. Furthermore, Tubg1 Y92C/+ animals show neuroanatomical and behavioral defects and increased epileptic cortical activity. We show that Tubg1 Y92C/+ mice partially mimic the human phenotype and therefore represent a relevant model for further investigations of the physiopathology of cortical malformations.
TURKISH JOURNAL OF MEDICAL SCIENCES, 2020
Background and aim: The number of reports on the role of tubulin gene mutations (TUBA1A, TUBB2B, and TUBB3) in etiology of malformations of cortical development has peaked in recent years. We aimed to determine tubulin gene defects on a patient population with simple and complex malformations of cortical development, and investigate the relationship between tubulin gene mutations and disease phenotype.Materials and methods: We evaluated 47 patients with simple or complex malformations of cortical development, as determined by radiological examination, for demographic features, clinical findings and mutations on TUBA1A, TUBB2B, and TUBB3 genes. Results: According to the magnetic resonance imaging findings, 19 patients (40.5%) had simple malformations of cortical development and 28 (59.5%) patients had complex malformations of cortical development. Focal cortical dysplasia was the most common simple malformation, lissencephaly was the most common coexisting cortical malformation, and ...
Acta Neuropathologica Communications, 2014
Complex cortical malformations associated with mutations in tubulin genes are commonly referred to as "Tubulinopathies". To further characterize the mutation frequency and phenotypes associated with tubulin mutations, we studied a cohort of 60 foetal cases. Twenty-six tubulin mutations were identified, of which TUBA1A mutations were the most prevalent (19 cases), followed by TUBB2B (6 cases) and TUBB3 (one case). Three subtypes clearly emerged. The most frequent (n = 13) was microlissencephaly with corpus callosum agenesis, severely hypoplastic brainstem and cerebellum. The cortical plate was either absent (6/13), with a 2-3 layered pattern (5/13) or less frequently thickened (2/13), often associated with neuroglial overmigration (4/13). All cases had voluminous germinal zones and ganglionic eminences. The second subtype was lissencephaly (n = 7), either classical (4/7) or associated with cerebellar hypoplasia (3/7) with corpus callosum agenesis (6/7). All foetuses with lissencephaly and cerebellar hypoplasia carried distinct TUBA1A mutations, while those with classical lissencephaly harbored recurrent mutations in TUBA1A (3 cases) or TUBB2B (1 case). The third group was polymicrogyria-like cortical dysplasia (n = 6), consisting of asymmetric multifocal or generalized polymicrogyria with inconstant corpus callosum agenesis (4/6) and hypoplastic brainstem and cerebellum (3/6). Polymicrogyria was either unlayered or 4-layered with neuronal heterotopias (5/6) and occasional focal neuroglial overmigration (2/6). Three had TUBA1A mutations and 3 TUBB2B mutations. Foetal TUBA1A tubulinopathies most often consist in microlissencephaly or classical lissencephaly with corpus callosum agenesis, but polymicrogyria may also occur. Conversely, TUBB2B mutations are responsible for either polymicrogyria (4/6) or microlissencephaly (2/6).