to develop the disease in midlife. GENETIC COUNSEL-
ING is almost always a valuable and necessary
component of genetic testing.
See also ETHICAL ISSUES IN GENETICS AND MOLECU-
LAR MEDICINE; GENETIC PREDISPOSITION; LIFESTYLE AND
HEALTH.
genome The total genetic material, including
coding and noncoding sequences, a cell contains
in its chromosomes. Each organism has a unique
genome. Scientists define the size of a genome by
the number of its base pairs. The human genome
contains 3.2 billion base pairs, which make up
that comprise about 23,000 genes.
See also CELL STRUCTURE AND FUNCTION; CHROMO-
SOME; GENE; GENOTYPE; HUMANGENOMEPROJECT; PHE-
NOTYPE.
genotype The contents of an individual’s GENETIC
CODE. The genotype directs the structures and func-
tions of the human body. A person’s genotype is to
the human body what an architect’s blueprint is to
a house: It provides the directions for the construc-
tion and operation of the human organism.
See also GENOME; KARYOTYPE; PHENOTYPE.
G6PD deficiency An inherited genetic disorder
in which the body lacks the enzyme glucose-6-
phosphate dehydrogenase (G6PD). Erythrocytes
(red BLOODcells) normally produce G6PD, which
aids in metabolizing carbohydrates and also helps
to protect erythrocytes from oxidation (damage
resulting from metabolic waste). The absence of
G6PD causes health problems when the body
experiences unusual stress, such as illness, or with
certain medications such as aspirin and sulfa
antibiotics. These circumstances cause oxidants to
accumulate in the blood. Without G6PD to neu-
tralize these oxidants, they destroy erythrocytes,
resulting in hemolytic ANEMIA.
The symptoms of hemolytic anemia resulting
from G6PD deficiency include- dark URINE
- pale SKIN
- weakness
- JAUNDICE (yellowish discoloration of the skin
and sclera of the eyes)
- HEPATOMEGALY(enlarged LIVER) and SPLENOMEGALY
(enlarged SPLEEN) - tachycardia (rapid HEART RATE)
- FEVER
Symptoms and family history may cause the
doctor to suspect G6PD deficiency. Blood tests will
reveal the hemolytic anemia. Treatment generally
consists of avoiding circumstances and substances
that trigger oxidative stress. Many people are able
to avoid symptoms entirely through such an
approach. Because G6PD is an inherited condition,
there are no methods for prevention. The inheri-
tance pattern for G6PD is X-linked recessive;
G6PD affects twice as many males as females and
is more prominent in people of African American
heritage and Mediterranean heritage.
See also ERYTHROCYTE; GENETIC DISORDERS; INHERI-
TANCE PATTERNS; PHENYLKETONURIA(PKU); PORPHYRIA.G6PD deficiency 131