DLGAP2 and intervertebral disk degenerative disorder: Of the five genes differentially methylated with exposure to maternal smoking, DLGAP2 (discs large homolog-associated protein 2) is of particular importance for IDD, since rare variants in DLGAP2 were identified in progressive epilepsy with mental retardation (EPMR [MIM#610003) [58] as well as ASD [59].