Webster's New World Medical Dictionary

Mantle cell lymphoma
A type of non-Hodgkin’s
lymphoma that originates from a specific type of B
lymphocytes. Abbreviated MCL. Most cases of MCL
are associated with a specific chromosome translo-
cation, t(11;14). MCL has a poor prognosis.
MAO
Monoamine oxydase, an enzyme that is
active in the nervous system. All the effects of MAO
are not known, but it is known that MAO acts against
the neurotransmitter epinephrine.
MAO inhibitor
One of a family of medications
(brand names: Aurorex, Nardil, Parnate) that act to
limit the activity of monoamine oxydase (MAO) in
the nervous system. MAOIs are prescribed to treat
depression, anxiety, migraine, and selected other
conditions in patients who are not responsive to
other medications. They interact with many over-
the-counter medications and some foods, so
patients taking MAOIs must be educated about what
to avoid and must follow a restricted diet.
MAOI
Monoamine oxidase (MAO) inhibitor.
map-dot-fingerprint type corneal dystrophy
See 
Cogan corneal dystrophy.
maple syrup urine disease
A hereditary dis-
ease that is due to deficiency of an enzyme involved
in amino acid metabolism, characterized by urine
that smells like maple syrup. In maple syrup urine
disease, the three branched-chain amino acids
(leucine, isoleucine, and valine) cannot be metabo-
lized (processed), and they build up in the blood,
causing problems with brain function and leading to
mental retardation, physical disability, and death, if
not treated. Treatment involves use of a special diet
and monitoring of protein intake.
mapping
See 
gene mapping.
mapping, gene
See 
gene mapping.
marasmus
See 
cachexia.
Marfan syndrome
An inherited disorder of con-
nective tissue that is characterized by abnormalities
of the eyes, skeleton, and cardiovascular system.
Nearsightedness (myopia) is the most common eye
feature in Marfan syndrome. Displacement of the
lens from the center of the pupil occurs in more
than half of patients. Patients with Marfan syndrome
have an increased risk for retinal detachment, glau-
coma, and early cataracts. The skeleton shows bone
overgrowth and loose joints. The arms and legs are
unusually long, as are the fingers and toes. Due to
overgrowth of the ribs, the sternum may be pushed
in (pectus excavatum) or out (pectus carinatum).
Scoliosis is common. Cardiovascular manifestations
in Marfan syndrome include enlargement of the
aorta at the level of the aortic valve, aortic
aneurysm, prolapse of the mitral and tricuspid
valves, and enlargement of the pulmonary artery.
The major causes of disease and death in the syn-
drome are related to the heart and blood vessels.
Marfan syndrome is inherited in an autosomal dom-
inant manner and is caused by mutation in the FBN1
gene that encodes fibrillin 1. About 75 percent of
people with Marfan syndrome have an affected par-
ent, and 25 percent have a new gene mutation.
Pregnancy can be dangerous for women with
Marfan syndrome because the aorta can widen.
Prevention of complications is key and includes
exercise, blood pressure control, monitoring of the
eyes, heart, and lungs, and physical therapy. Given