Poor signals. The imperforate anus can occur in isolation or as part of a syndrome. During fetal development the gut starts as a sausage like mass that forms a central cavity, lengthens & moves down from the inside to join up with the external skin at the anus. The defect can be as minimal as a thin membrane in normal position or gut ending far from the anus. Poor signal decoding triggers this defect.
Down, VACTER-L. Anal atresia is most commonly associated with the vacterl association (vertebral, anal atresia, cardiac, tracheoesophageal fistula, renal, limb anomalies), and occurs with increased frequency in trisomy 21 (down syndrome).
No. There are no genetic causes known for imperforate anus or other factors like drugs or illnesses that can happen while pregnant.