DDAH1 and Compulsive behaviors: In addition, enrichment analyses showed that the following genes: melanocortin 1 receptor MC1R, tubulin Beta 3 (TUBB3), dimethylarginine dimethylaminohydrolase 1 (DDAH1), inositol monophosphatase 2 (IMPA2), and parathyroid hormone 2 receptor (PTH2R) could theoretically lead to coexistence of ASD and OCD.