Deletion or mutation of the topo IIIβ gene is linked to schizophrenia and autism.[53,57,58] In Drosophila, neuronal synapse formation was disrupted when an autism patient-derived mutation in topo IIIβ was introduced.[54] In addition, a disease-linked mutation in FMRP (I304N) from a Fragile X syndrome patient was shown to disrupt the interaction between FMRP and TDRD3/topo IIIβ. The gene discussed is FMR1; the disease is fragile X syndrome.