Classical Homocystinuria (HCU) is a rare inborn error of methionine metabolism caused by a deficiency of cystathionine-ß-synthase (CBS). This enzyme is involved in the transsulfuration of homocysteine to cysteine and lack of CBS results in an increased plasma concentration of homocysteine, methionine and other sulphur containing metabolites and in low levels of plasma cysteine, cystathionine and serine.

Treatment strategies aimed at lowering total homocysteine may be pharmacological or dietary or a combination of both.

(1) Pharmacological doses of pyridoxine (B6) lead to an increase of residual CBS activity in B6 responsive HCU. Response to B6 is variable and is influenced by folate depletion. Folate is therefore given in conjunction with B6. Betaine will lower the plasma homocysteine whilst raising the less toxic methionine through the process of remethylation.

(2) Dietary treatment aims to reduce the plasma concentration of total homocysteine by means of a methionine restricted, cystine enriched, diet in those who are non-pyridoxine or partially pyridoxine responsive.

Essential components of diet:

• Methionine from normal dietary sources - since methionine is an essential amino acid it cannot be excluded but must be restricted to individual tolerance and measured using an exchange system of either 1g protein exchanges or 20mg methionine exchanges

• Protein Substitute - supplementation with methionine-free amino acids to meet or slightly exceed total protein requirements

• Comprehensive vitamin, mineral and trace mineral supplement is required because of the severe dietary restriction and limited range of foods permitted

• Cystine - some centres recommend additional supplements of Cystine over and above that provided in the protein substitute, aimed at correcting the low plasma concentration of cystine.

Due to the rarity of this condition there is a very limited choice of dietary products available to treat HCU.

Vitaflo have developed a range of protein substitutes for patients with homocystinuria:

1. HCU gel (1-10 years)

2. HCU express (8 years +)

3. Cystine Amino Acid Supplement

HCU gel and HCU express have been specifically designed to be low volume nutritionally complete protein substitutes. They are quick and easy to prepare and to drink thus setting a new standard of acceptance and convenience and meeting the needs of this patient group.

Cystine Amino Acid Supplement is available in powder form and can be easily incorporated into the diet when required.