Before she wrote her infamous post about the Hole in the Bucket, Ginger Houston-Ludlam had written another post on one of the DS parent lists (I think it was DS-Nutrition, I haven’t been able to check the archives yet to get the date) to explain the workings of the SAM and Folate cycles. Ginger wrote the “wipers on the bus go trap, trap, trap” to explain in simple terms what happens in Down syndrome in DNA methylation, its connection to leukemia, and what parents can do about it.
At the B12 station, the folate bus line connects with the SAM bus line. Passengers (“methyl groups” in this case) get off the folate bus line and transfer to the SAM bus line. The methyl groups get onto a bus labeled “Homocysteine,” at which point it changes its name to “Methionine.” The methionine bus then goes to the station where it becomes “SAM.” The methyl groups get off the bus at the SAM station and go on to do a lot of very important stuff in the body, such as methylating DNA.
In Down Syndrome, the homocysteine busses are being hijacked to the CBS station because CBS is triplicated, and so there are no busses available to pick up the methyl groups who are milling around grumbling at the B12 station waiting to get on the homocysteine bus. Because there are no homocysteine busses available to take the methyl groups around to the SAM station, the chemicals (like DNA) waiting for the methyl groups at the SAM station can’t go about their business either. The methyl-folate is “trapped” there.
If you are not yet comfortable with these concepts, and yet you want to understand your child’s blood tests, take some time with these articles. Study the diagrams. Say the big words out loud. Then go to check if your DS child’s vitamin supplement contains TMG and sufficient folic acid or folinic acid, and B12.
Filed under: biocchemistry Tagged: | folate, homocysteine, leukemia, MTHFR, SAM
