Mirror-image asymmetry in monozygotic twins with kabuki syndrome

Kabuki syndrome (OMIM 147920) is a rare disorder characterised by moderate intellectual disability, growth retardation, microcephaly and characteristic facial dysmorphic features which comprise long palpebral fissures, eversion of the lateral third of the eyelids and arched eyebrows with lateral sparseness. Mutations in MLL2 are the most frequent cause of this disorder. More than 100 MLL2 point mutations have been reported, but large intragenic deletions comprising one or more exons have not yet been identified. We report on a pair of monozygotic twin brothers in whom a deletion of 2 neighbouring exons was detected. The twins had the characteristic facial features of Kabuki syndrome, and they suffered from microcephaly, cleft lip and palate and congenital heart disease. Cleft lip and palate were left-sided in the first twin and right-sided in the second twin, i.e. they represented a mirror-image asymmetry. The intragenic deletion in these brothers broadens the spectrum of MLL2 mutations, and they provide a rare example of mirror-image asymmetry of congenital malformations in monozygotic twins.