The case highlights the need to investigate all cases of venous and arterial thrombosis to find out the cases of Hyperhomocystenuria/Hyperhomocysteinemia. This is almost imperative in all cases of younger patients, who should not normally have stasis induced DVT. The incidence is quoted to be anything between 1: 50,000 to 1: 100,000 of population. The important fact is that mere anti-coagulation is not enough in these cases. I have encountered cases where the thrombosis has occurred while being anticoagulated with warfarin/acetrom. It is only when the supplements of Folic Acid, Pyridoxine and Cynocobalamin are given in therapeutic doses that a tangible clinical response is seen.
Answering specific questions:
The cause of the disease is an error in the metabolism of the amino acid methionine due to absence of a certain enzyme. This is an inborn error and cannot be corrected but can be kept under control by taking the required vitamins.
The absorption of these vitamins is quite good anyway but it is better to take these in therapeutic doses and, as these are readily available and inexpensive, it is better to take these in the medicine form rather than look for foods rich in these.
I think the second question answers this part as well. The Cynocobalamin is an injection to be given once a month and other two are tablets which are absorbed well.