Summary: Homocystinuria caused by Cystathionine Beta-Synthase (CBS) Deficiency is a rare autosomal-recessive metabolic condition characterized by an excess of homocysteine (Hcy) in the plasma, tissues and urine. It is due to reduced or absent activity of the CBS enzyme, and is also known as classical homocystinuria. The symptoms associated with homocystinuria are variable in severity and time of onset acro...