Subjects having at least one condition selected from the group consisting of mental retardation, Down's syndrome, fragile X syndrome and autism are treated with a composition that includes gamma-am inobutyric acid agonists and/or Ml muscarinic rreceptor antagonists. The gamma-am inobutyric acid agonist (GABA) can be a GABA(B) agonist, such as baclofen. GABA(B) agonists can be used in combination with Group I mGluR antagonists and Ml muscarinic receptor antagonists in methods of treating humans.
METHODS OF TREATING MENTAL RETARDATION, DOWN'S SYNDROME, FRAGILE X SYNDROME AND AUTISM