Webster's New World Medical Dictionary

DMD
Duchenne muscular dystrophy. See 
muscu-
lar dystrophy, Duchenne.
DNA 1
Deoxyribonucleic acid, one of the two mol-
ecules (along with RNA) that encode genetic infor-
mation. DNA is double-stranded. The two strands are
held together by weak hydrogen bonds between base
pairs of nucleotides to form a double helix. The dou-
ble helix looks something like an immensely long
ladder twisted into a helix, or coil. The sides of the
ladder are formed by a backbone of sugar and phos-
phate molecules, and the rungs consist of nucleotide
bases joined in the middle by the hydrogen bonds.
The four nucleotides in DNA contain the bases ade-
nine (A), guanine (G), cytosine (C), and thymine
(T). 
2
In the UK, an abbreviation for “did not
attend,” comparable to the US term “no-show” for a
patient who missed an appointment.
DNA, mitochondrial
The DNA of the mitochon-
drion, a structure situated in the cytoplasm of the
cell rather than in the nucleus, where all the other
chromosomes are located. Abbreviated mtDNA.
mtDNA is inherited from the mother. There are 2 to
10 copies of the mtDNA genome in each mitochon-
drion. mtDNA is a double-stranded, circular mole-
cule. It is very small compared to the chromosomes
in the nucleus, and it contains only a limited number
of genes. It is specialized in the information it car-
ries, and it encodes a number of the subunits in the
mitochondrial respiratory-chain complex that the
cell needs in order to respire. Mutations (changes)
in mtDNA can cause disease, and they often impair
the function of oxidative-phosphorylation enzymes in
the respiratory chain, especially in tissues with high
energy expenditure, such as brain and muscle tis-
sues. See also 
mitochondrial disease.