Tubulin plays an essential role in cortical development, and TUBA1A encodes a major neuronal α-tubulin. Neonatal mutations in TUBA1A are associated with severe brain malformations, and approximately 70% of patients with reported cases of TUBA1A mutations exhibit lissencephaly. We report the case of a 1-year-old boy with the TUBA1A nascent mutation c.1204C >T, p.Arg402Cys, resulting in lissencephaly, developmental delay, and seizures, with a brain MRI showing normal cortical formation in the bilateral frontal lobes, smooth temporo-parieto-occipital gyri and shallow sulcus. This case has not been described in any previous report; thus, the present case provides new insights into the broad disease phenotype and diagnosis associated with TUBA1A mutations. In addition, we have summarized the gene mutation sites, neuroradiological findings, and clinical details of cases previously described in the literature and discussed the differences that exist between individual cases of TUBA1A mutations through a longitudinal comparative analysis of similar cases. The complexity of the disease is revealed, and the importance of confirming the genetic diagnosis from the beginning of the disease is emphasized, which can effectively shorten the diagnostic delay and help clinicians provide genetic and therapeutic counseling.

Tubulinopathies are associated with malformations of cortical development but not Walker-Warburg Syndrome. Intensive monitoring of a Croatian infant presenting as Walker-Warburg Syndrome in utero began at 21 weeks due to increased growth of cerebral ventricles and foetal biparietal diameter. Monitoring continued until Caesarean delivery at 34 weeks where the infant was eutrophic. Clinical assessment of a progressive neurological disorder of unknown aetiology found a macrocephalic head and markedly hypoplastic genitalia with a micropenis. Neurological examination showed generalized hypotonia with very rare spontaneous movements, hypotonia-induced respiratory insufficiency and ventilator dependence, and generalized myoclonus intensifying during manipulation. With clinical features of hypotonia, lissencephaly, and brain malformations, Walker-Warburg Syndrome was suspected; however, eye anomalies were absent. Genetic trio analysis via whole-exome sequencing only identified a novel de novo mutation in the TUBA1A gene (NM_006009.4:c.848A>G; NP_006000.2:p.His283Arg) in the infant, who died at 2 months of age, as the likely cause. We report a previously unpublished, very rare heterozygous TUBA1A mutation with clinical features of macrocephaly and hypoplastic genitalia which have not previously been associated with the gene. The absence of eye phenotypes or mutations in Walker-Warburg-associated genes confirm this as not a new presentation of Walker-Warburg Syndrome but a novel TUBA1A tubulinopathy for neonatologists to be aware of.

Lissencephaly is a rare brain malformation characterized by abnormal neuronal migration during cortical development. In this study, we performed a comprehensive genetic analysis using next-generation sequencing in 12 unsolved Japanese lissencephaly patients, in whom PAFAH1B1, DCX, TUBA1A, and ARX variants were excluded using the Sanger method. Exome sequencing (ES) was conducted on these 12 patients, identifying pathogenic variants in CEP85L, DYNC1H1, LAMC3, and DCX in four patients. Next, we performed genome sequencing (GS) on eight unsolved patients, and structural variants in PAFAH1B1, including an inversion and microdeletions involving several exons, were detected in three patients. Notably, these microdeletions in PAFAH1B1 could not to be detected by copy number variation (CNV) detection tools based on the depth of coverage methods using ES data. The density of repeat sequences, including Alu sequences or segmental duplications, which increase the susceptibility to structural variations, is very high in some lissencephaly spectrum genes (PAFAH1B1, TUBA1A, DYNC1H1). These missing CNVs were due to the limitations of detecting repeat sequences in ES-based CNV detection tools. Our study suggests that a combined approach integrating ES with GS can contribute to a higher diagnostic yield and a better understanding of the genetic landscape of the lissencephaly spectrum.

Malformations of cortical development (MCD) are a group of disorders affecting the normal development of the human cortex and are significant causes of delay in psychomotor development and epilepsy in children. Lissencephaly (smooth brain) forms a major group of brain malformations. Microtubules help in the migration of neuronal cells. Defect in tubulin gene alpha-tubulin (TUBA), beta-tubulin (TUBB), and gamma-tubulin (TUBG) leads to defective neuronal migration. This group of disorders is termed as "tubulinopathies." The important genes implicated in causing lissencephaly are LIS1, XLIS, and TUBA1A gene. Recently, a mutation in the TUBG1 gene is associated with it. Here, we report a one-and-a-half-year-old girl with global developmental delay, microcephaly, infantile-onset epilepsy, epileptic spasms, dysmorphism, and motor signs. There was no significant birth history. Neuroimaging (MRI) showed a broad thick gyri and a decreased number of sulci suggestive of lissencephaly/pachygyria spectrum. There was dilatation of the ventricles, and no grey matter heterotopia was noted. Sleep EEG showed multifocal epileptiform discharges. The child was treated with multiple anti-seizure medicines (ASMs). A genetic test, whole exome sequencing, was done to determine the etiology of MCD. A heterozygous missense variation in exon 6 of the TUBG1 gene was identified and reported as a "variant of unknown significance." Still, because the genotype matched with the clinical phenotype of the patient, it was considered clinically significant. Therefore, a complete diagnosis of TUBG1 mutation-associated cortical malformation (lissencephaly/pachygyria) with microcephaly and early-onset epilepsy was established. TUBG1 mutation is de novo in most cases, but parental testing is recommended. The parents of such patients need to be counseled about the need for prenatal testing and the risk of the disease to siblings. The overall prognosis in such cases is poor because of refractory seizures, physical limitations, and intellectual disability.

Microtubules are dynamic cytoskeletal structures involved in several cellular functions, such as intracellular trafficking, cell division and motility. More than other cell types, neurons rely on the proper functioning of microtubules to conduct their activities and achieve complex morphologies. Pathogenic variants in genes encoding for α and β-tubulins, the structural subunits of microtubules, give rise to a wide class of neurological disorders collectively known as "tubulinopathies" and mainly involving a wide and overlapping range of brain malformations resulting from defective neuronal proliferation, migration, differentiation and axon guidance. Although tubulin mutations have been classically linked to neurodevelopmental defects, growing evidence demonstrates that perturbations of tubulin functions and activities may also drive neurodegeneration. In this study, we causally link the previously unreported missense mutation p.I384N in TUBA1A, one of the neuron-specific α-tubulin isotype I, to a neurodegenerative disorder characterized by progressive spastic paraplegia and ataxia. We demonstrate that, in contrast to the p.R402H substitution, which is one of the most recurrent TUBA1A pathogenic variants associated to lissencephaly, the present mutation impairs TUBA1A stability, reducing the abundance of TUBA1A available in the cell and preventing its incorporation into microtubules. We also show that the isoleucine at position 384 is an amino acid residue, which is critical for α-tubulin stability, since the introduction of the p.I384N substitution in three different tubulin paralogs reduces their protein level and assembly into microtubules, increasing their propensity to aggregation. Moreover, we demonstrate that the inhibition of the proteasome degradative systems increases the protein levels of TUBA1A mutant, promoting the formation of tubulin aggregates that, as their size increases, coalesce into inclusions that precipitate within the insoluble cellular fraction. Overall, our data describe a novel pathogenic effect of p.I384N mutation that differs from the previously described substitutions in TUBA1A, and expand both phenotypic and mutational spectrum related to this gene.