Webster's New World Medical Dictionary

homocysteine
An amino acid that is produced by
the human body, usually as a byproduct of consum-
ing meat. Homocysteine is normally converted into
other amino acids. An abnormal accumulation of
homocysteine, which can be measured in the blood,
can be a marker for the development of heart dis-
ease. Elevated levels of homocysteine in the blood
appear to increase the risk of heart attack, stroke,
peripheral vascular disease, and venous thrombo-
embolism (blood clots in the veins). Homocysteine is
believed to damage blood vessels in several ways. It
injures the cells that line arteries and stimulates the
growth of smooth muscle cells. Homocysteine can
also disrupt normal blood clotting mechanisms.
Elevated levels of homocysteine also appear to
increase the risk of Alzheimer’s disease. The ways to
lower homocysteine are to eat less meat and take
supplements of the B vitamins folic acid (folate),
B6, and B12 that are needed by the enzymes that
process homocysteine.
homocystinuria
A genetic disease that is due to
an enzyme deficiency that permits a buildup of the
amino acid homocysteine. Progressive mental retar-
dation is common, but does not always occur, in
untreated cases of homocystinuria. The finding of
vascular disease and premature arteriosclerosis in
persons with homocystinuria led to the theory that
homocysteine may be a factor in heart disease.
Homocystinuria is inherited in an autosomal reces-
sive manner and is one of the diseases commonly
included among the diseases for which newborns
are screened. Treatments include special diets and
vitamin B6.
homolog 1
One chromosome of a pair.
2
A
gene from one species that has a common origin
and functions the same as a gene from another
species. Also spelled homologue.