BUB1B and microcephaly: In this regard, the dissimilar disease expression in carriers of biallelic pathogenic variants in another MVA gene, BUB1B, is mentionable: the initially reported 5 families with the BUB1B-associated MVA1 subtype displayed an — albeit variable — childhood-onset MVA phenotype with intrauterine growth retardation, microcephaly, neurological abnormalities, and, in 2 families, cancer (7).