G
6
PD DEFICIENCY
G
G6PD deficiency
An
X-linked disorder
in w hich an abnor-
mal gene causes a deficiency of G
6
PD
(the
enzyme
glucose
6
phosphate de-
hydrogenase) in red blood cells. In a
healthy person, this enzyme contributes
to a chemical process that protects the
cells from
damage. G
6
PD
deficiency
makes the red cells prone to damage or
destruction by infectious illness or by
certain drugs or foods.
The disorder most commonly affects
southern
European
and
black
men.
Women are unaffected but they can
carry the abnormal gene and are at risk
of passing it on to their sons.
Some drugs, such as certain
antimalar-
ial drugs
and
antibiotics
,
may precipitate
haemolysis (destruction of red cells) in
people with the abnormal gene; see the
table below for drugs that may pose this
risk. In one form of G
6
PD deficiency,
called
favism,
haemolysis may be trig-
gered by a chemical in broad beans, and
affected people must avoid eating them.
After taking a precipitating drug or
food, or during an infectious illness, an
affected person develops symptoms of
anaemia (see
anaemia, haemolytic
) ,
such
as
jaundice
,
fatigue,
headaches,
and
shortness of breath (which may occur
even after m ild exertion).
G
6
PD deficiency is diagnosed with a
blood test. There is no specific treatment
available, but symptoms provoked by a
drug or food can, however, be prevented
by avoiding that substance.
GABA
The
abbreviation
for
gamma-amino-
butyric acid. This chemical is a
neuro-
transmitter
(a chemical released from
nerve
endings
that
relays
messages
within the
nervous system
) .
GABA con-
trols the flow of nerve impulses by
blocking the release of other neuro-
transmitters, such as
noradrenaline
and
dopamine
,
that stimulate electrical acti-
vity in the nerve cells; as a result, this
activity is inhibited.
The action of GABA is enhanced by
benzodiazepine drugs
,
anticonvulsant drugs
,
and possibly
alcohol
.
In contrast, it has
been suggested that people with
Hunt-
ington’s disease
(an inherited disorder
that causes a loss of brain function and
abnormal
movements)
suffer
degen-
eration of GABA-secreting brain cells,
leading to overstimulation of the
basal
ganglia
(an area of the brain that helps
coordinate movement) and producing
the typical symptoms.
gabapentin
An
anticonvulsant drug
used either alone
or with other anticonvulsants to treat
some types of
epilepsy
.
Common side
effects include
drowsiness,
dizziness,
unsteadiness, and fatigue.
gag reflex
An automatic impulse to retch, brought
about by the
autonomic nervous system
in
response to a particular stimulus, such
as a foreign object touching the back of
DRUGS TO BE AVOIDED BY PEOPLE WITH G6PD DEFICIENCY
Class
Drugs to avoid
Antimalarial drugs
Primaquine, chloroquine*, quinine*, quinidine*,
dapsone
Antibacterial and antibiotic drugs
Nitrofurantoin, sulphonamides
(such as co-trimoxazole), quinolone drugs
(such as ciprofloxacin and nalidixic acid)
Analgesics (painkillers)
Aspirin*
Miscellaneous
Vitamin K (water-soluble form), probenecid
*These drugs do not usually cause problems in the type ofG6PD deficiency that affects blackpeople.
the throat. The reflex protects the airway
from becoming blocked by debris. If a
person becomes unconscious, however,
the gag reflex may be lost, and the per-
son may be at risk of choking.
gait
A term used to describe the manner or
style of
walking
.
Gait varies from one
person to another. An abnormal gait, or
an unusual change in the gait, may
indicate a neuromuscular or brain dis-
order (such as
Parkinson’s disease
) .
(See
also
festinating gait
. )
galactocele
A
breast cyst
that contains milk or a
milky substance. A galactocele can be
caused by obstruction of a milk duct in
the
breast
during
breast-feeding
.
In most
cases, it occurs at the end of breast-
feeding
when
milk
is
allowed
to
stagnate in the breast. The swelling may
occasionally become infected, leading
to a
breast abscess
.
Usually, no treatment
is needed; the fluid is reabsorbed, or
can be expelled by massaging the breast
towards the nipple.
galactokinase deficiency
A rare, inherited condition in w hich
there is a deficiency of galactokinase, an
enzyme
involved in the breakdown of
galactose (a simple sugar that is derived
from the m ilk sugar
lactose
) .
Galactoki-
nase deficiency is an autosomal recessive
genetic disorder
. T h e
condition leads to a
form of
galactosaemia
(the inability of
the body to convert galactose into
glu-
cose
,
another simple sugar). The only
manifestation
of
galactokinase
defi-
ciency galactosaemia is
cataracts
,
w hich
usually become apparent in affected
babies w ithin the first few weeks of life.
galactorrhoea
The spontaneous, persistent production
of breast m ilk by a woman who is
not pregnant or
breast-feeding
,
or, very
rarely, by a man. Lactation (m ilk pro-
duction) is initiated by a rise in the
level of
prolactin
,
a hormone produced
by the
pituitary gland
.
Galactorrhoea is
caused by excessive secretion of pro-
lactin due either to a
pituitary tumour
or
to another endocrine disorder, such as
hypothyroidism
.
It may also be caused by
some
antipsychotic drugs
.
As well as triggering breast milk pro-
duction, excess prolactin may adversely
affect the
ovaries
,
causing
amenorrhoea
(absence
of
menstrual
periods)
or
328
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