Webster's New World Medical Dictionary

gastrostomy, percutaneous endoscopic
A sur-
gical procedure for placing a feeding tube that does
not necessitate performing an open laparotomy
operation on the abdomen. Abbreviated PEG. An
endoscope is passed through the mouth, throat, and
esophagus to the stomach. The surgeon then makes
a small incision in the skin of the abdomen, pushes
an IV tube through the skin into the stomach, and
then sutures (ties) the tube in place. PEG is used for
feeding as well as administering medications.
Gaucher disease
A series of disorders that are
due to deficient activity of the enzyme glucocere-
brosidase, which leads to accumulation of gluco-
cerebroside in tissues of the body. The five types of
Gaucher disease encompass a continuum of clinical
findings from a lethal form that occurs before or
just after birth to a form so mild that it may not be
diagnosed until old age. All types of Gaucher disease
are inherited in an autosomal recessive manner.
gender identity disorder
See 
transsexualism.
gene 1
In classical genetics, a unit of inheritance.
2
In molecular genetics, a sequence of chromoso-
mal DNA that is required to make a functional 
product.
gene, breast cancer susceptibility
See 
breast
cancer susceptibility gene.
gene, evolutionarily conserved
A gene that
has remained essentially unchanged throughout
evolution. Conservation of a gene indicates that it is
unique and essential. Changes in the gene are likely
to be lethal.
gene, target
The primary gene of concern. See
also 
gene, marker.
gene, zygotic lethal
A gene that is fatal for the
zygote, the cell formed by the union of a sperm and
an egg. The zygote would normally develop into an
embryo, as instructed by the genetic material within
the unified cell. However, a zygotic lethal gene kills
prenatal development at its earliest point. A zygotic
lethal gene is a mutated version of a normal gene
that is essential to the survival of the zygote.