Using the PCR-free whole-genome sequencing data from 10 cases, we searched for known pathogenic trinucleotide repeat polymorphisms (e.g., C9orf72 and frontotemporal dementia) using ExpansionHunter along with a similar in-house approach (that previously identified a pathogenic Huntington’s disease CAG-repeat expansion33). The gene discussed is C9orf72; the disease is juvenile Huntington disease.