A girl suffering from growth retardation inherited a small genetic deletion on chromosome 11p15.5 from her healthy father. By molecular genetic tests the region was characterised, and it turned out that the deletion affected the imprinted KCNQ1OT1 gene, i.e. a gene which is expressed only from the paternal allele. Since the father inherited the same deletion from his mother, he was not affected because the maternally inherited gene copy is silenced. The identification of this genetic variants provides further insights in the complex regulation of imprinted genes, as it is the smallest variant reported so far for this region. (By Prof. Thomas Eggermann, https://jmg.bmj.com/content/early/2020/05/23/jmedgenet-2020-106868 )