Turner syndrome is a chromosomal disorder associated with the complete or partial absence of an X chromosome. The disease is Turner syndrome (Monarch Disease Ontology entry MONDO_0019499). Also known as: 45,X gonadal dysgenesis, 45,X syndrome, 45,X/46,XX syndrome, 45,X0 syndrome, 45X syndrome, XO syndrome, gonadal dysgenesis - Turner, karyotype 45, X.