Treatment and monitoring of the disorders of homocystinuria
| HCU | MTHFR | Cobalamin disorders | ||
| Pyridoxine-responsive (partial or fully) | Pyridoxine non-responsive | |||
| Main treatment | High-dose pyridoxine | Low protein diet with methionine-free amino acid supplement; cystine | Betaine | High-dose vitamin B12 as intramuscular hydroxocobalamin |
| Additional treatment | Betaine (required if partially pyridoxine-responsive) | Betaine | Folate derivative (mefolinate or folinic acid) | Betaine |
| Treatment to consider | Vitamin B12; folate | Vitamin B12; folate | Methionine | Folinic acid; Methionine |
| Monitor | Total homocysteine; methionine if on betaine Symptoms of peripheral neuropathy if on high-dose pyridoxine | Total homocysteine; methionine; quantitative amino acids if on low protein diet Symptoms of cerebral oedema on betaine | Total homocysteine; methionine; consider CSF folate analysis after starting treatment Symptoms of cerebral oedema on betaine | Total homocysteine; methionine; haemoglobin and mean cell volume |
CSF, cerebrospinal fluid; HCU, classical homocystinuria; MTHFR, methyltetrahydrofolate reductase deficiency.