DM2 is caused by a defect of the CNBP gene on chromosome 3.[12] The specific defect is a repeat of the cytosine-cytosine-thymine-guanosine (CCTG) tetranucleotide in the CNBP gene.[12] As it involves the repeat of four nucleotides, it is not a trinucleotide repeat disorder, but rather a tetranucleotide repeat disorder.[13][14]