Microcephaly, growth restriction, and increased sister chromatid exchange

Microcephaly, growth restriction, and increased sister chromatid exchange (MGRISCE) is characterized by prenatal onset growth restriction and microcephaly. Diagnostically, a hallmark feature is the presence of increased sister chromatid exchanges on cytogenetic testing. MGRISCE1, caused by biallelic mutations in BLM, is known as Bloom syndrome [DS:H01346]. Recently, MGRISCE2, caused by mutations in TOP3A, has been reported. TOP3A encodes topoisomerase III alpha, which binds to BLM as part of the BTRR complex, and promotes dissolution of double Holliday junctions arising during homologous recombination.