Anybody know about homocysteine?

Yes.: Homocysteine is a toxic metabolite of methionine metabolism. It is converted to the non-toxic form, homocystine by a series of enzymes. People missing one of those enzymes can develop high levels of homocysteine, enough to spill over into their urine, homocysteinuria. Children with this have heart attacks and strokes by 5 or 6 years of age, and half are dead by 20. But levels have to be very high.

Toxic to endothelium: Accelerated vascular disease. Two breakdown pathways rely on folic acid; one with b6; two with b12. Too lower this, you should take a combination of all three! it's level will rise when any or all of these nutrients are low, most common in folate and B12 deficiencies.