Pathogenic correlation between mosaic variegated aneuploidy 1 (MVA1) and a novel BUB1B variant: a reappraisal of a severe syndrome

Background: The BUB 1 mitotic checkpoint serine/threonine kinase B (BUB1B) gene encodes a key protein in the mitotic spindle checkpoint, which acts as a surveillance mechanism, crucial for the maintenance of the correct chromosome number during cell deviation. Mutations of BUB1B gene are linked to mosaic variegated aneuploidy 1 (MVA1) syndrome, a rare autosomal recessive disorder characterized by widespread mosaic aneuploidies, involving different chromosomes and tissues. MVA1 is clinically characterized by intrauterine growth restriction, post-natal growth retardation, and severe neurologic impairment including microcephaly, developmental delay/intellectual disability, epileptic seizures, and generalized hypotonia. Malignancies are also serious sequelae associated with the disorder. We reported on a case of two-year-old Italian girl with MVA1 who shows severe neurologic impairment, microcephaly and epileptic seizures. Materials and methods: Clinical data collection and genetic diagnosis of the patient were assessed. Mutational analysis covers the chromosomal microarray analysis, the gene methylation pattern studied using the methylation-specific multiplex ligation-dependent probe amplification, and the family-based Whole Exome Sequencing (WES). A literature research based on reported cases of MVA and premature chromatid separation was also included. Results: Karyotyping has revealed 12% of mosaics in the patient who carries a novel variant in BUB1B gene (c.2679A > T, p.Arg893Ser) detected by WES. Thirty-one cases of MVA1 including the present report, and four prenatally diagnosed cases with MVA1 were selected and inspected. Conclusion: Clinical and genetic findings reported in the girl strongly suggest a new MVA1 genotype-phenotype correlation and lead to a reappraisal of a severe syndrome. Diagnosis and in-depth follow-up provided worthwhile data.