In myotonic dystrophy type 2 the diagnosis is established by identification of a heterozygous pathogenic expansion of a CCTG repeat within a complex repeat motif, (TG)n(TCTG)n(CCTG)n, present in the CNBP (CCHC-type zinc finger, nucleic acid binding protein; previously known as zinc finger 9 gene, ZNF9) gene, located on the long arm of chromosome 3 (chr3q.21). The gene discussed is CNBP; the disease is myotonic dystrophy type 2.