Agenesis, sacral: Failure of formation of all or part of the sacrum (the lowest section of the spine).

Currarino syndrome is a condition characterized by the combination of:

• Partial absence of the sacrum (the lowest portion of spine),
• Anorectal (anal and rectal) abnormalities, and
• An abnormal mass in front of the sacrum (due to a meningocoele or teratoma).

The malformations in Currarino syndrome are all in tissues that have their embryological origin in the tail bud and may reflect disturbances in its formation during early embryonic life. A mutation (change) in a gene called the HLXB9 homeobox gene has been identified as responsible for autosomal dominant Currarino syndrome, also known as hereditary sacral agenesis.