DHX9 and cerebellar ataxia: DHX9: In patient T91 with SM (−2.8 SD), corpus callosum dysgenesis, DD, moderate ID, ataxia, hypotonia, convergent strabismus and dysmorphic facial features we identified a de novo variant NM_001357.5: c.3497G>C: p.(Arg1166Pro) in the DHX9 gene encoding the DNA and RNA helicase.