Brain malformations and mutations in α- and β-tubulin genes : a review of the literature and description of two new cases

Aim: 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.