ATM and ataxia telangiectasia: Pediatric patients with classical AT may present dystonia as the main manifestation, or even a first symptom, besides typical cerebellar ataxia, bulbar conjunctive telangiectasia, dysarthria, intellectual disability, stunted growth, etc. Most crucially, we found three novel pathogenic ATM gene mutation sites, c.437_440delTCAA, c.2482A>T, and c.5495_5496+2delAAGT, expanding the ATM pathogenic gene mutation spectrum.