1. Dietary management of classical homocystinuria (CBS deficiency)
Andrew Morris

2. Dietary protein Protein synthesis Methionine Homocysteine CBS
Pyridoxine
CBS
Homocysteine formation is minimised by giving enough methionine for protein synthesis but not much more
This needs a very low-protein diet & supplements of the other amino acids

3. Dietary treatment of babies
Combination of
Special formula that contains
All the normal ingredients except protein
All the amino acids except methionine
Breast milk or normal infant formula
To supply methionine for protein synthesis
Proportions of the two are adjusted to optimise blood homocysteine & methionine levels

4. Dietary treatment of older patients
Small, measured amounts of food containing protein
Methionine-free amino acid mixture
Adequate energy from low protein foods
most fruit & vegetables
synthetic e.g. low-protein bread, biscuits, pasta
Vitamin & mineral supplements
(included in most amino acid mixtures)
Adjusted to optimise homocysteine & methionine

5. Challenges in dietary treatment
Distance to specialist centre
Telephone advice & taking blood locally or measuring
homocysteine in bloodspots can reduce number of visits
Needle phobia may hamper monitoring
Play therapists can help to overcome this
Expense & (relative) unpalatability of supplements & low-protein foods
Health insurance & medical food companies should be
lobbied over these issues
Restrictions are unpopular leading to poor compliance

6. Factors contributing to poor compliance
Diagnosis after infancy
Adolescence
Attitude of family & friends
Personality
Newborn Screening can detect most patients with pyridoxine-unresponsive homocystinuria
Addition of Betaine can help if unable to reach homocysteine targets with diet alone
(Betaine alone seldom achieves adequate control)

7. Dietary protein
Protein synthesis
Methionine
Betaine
Homocysteine
CBS
Side effects of betaine
Taste, fishy odour at high doses
Methionine rises, seldom toxic but keep <1000 umol/l