In three families (3.33%), we observed recurrence of the de novo mutation in a following pregnancy: a family with osteogenesis imperfecta and a mutation in COL1A2 (OMIM: #120160), a family with Rett syndrome and a mutation in the MECP2 and a family with tuberous sclerosis and a mutation in the TSC1 (OMIM: #605284; Table 1). This evidence concerns the gene TSC1 and tuberous sclerosis.