Macrocephaly, hypospadias grade III-IV, and fragile X-like behavior in identical twins without involvement of the FMR-1 gene.

We present the distinct clinical symptoms and stigmata in 4.5 years old monozygotic male twins: macrocephaly, hypospadias grade III-IV, moderate mental retardation and fragile X-like behavior. Chromosome studies were normal and no FMR-1 mutation could be detected. We could not find other reports on the association of a fragile X-like clinical and behavioral phenotype and hypospadias grade III-IV.