Let's look at the Biochemistry part of Homocystinuria

  (S-adenosyl methionine)

1) Methionine -------------------------------> Homocysteine

• Homocysteine is formed from methionine through S-adenosyl methionine (sulfur containing amino acid)

      (Cystathionine Beta Synthase)

2) Homocysteine ------------------------------------> Cystathionine ----> Cysteine

• Enzyme Cystathionine beta synthase converts homocysteine to cystathionine which is then converted to cysteine

What is the problem in the pathway that causes the disorder?

• Due to deficiency of Cysthionine beta-synthase (CBS)

• Cysthionine beta-synthase catalyses the pathway during the catabolism of methionine to cysteine
• When there is deficiency of the (CBS), the step - homocysteine to cystathionine is blocked. Thus, leading to accumulation of homocysteine and methionine.