Webster's New World Medical Dictionary

hereditary angioneurotic edema
See
angioedema, hereditary.
hereditary hemorrhagic telangiectasia
A
genetic disease characterized by the presence of
multiple direct connections between arteries and
veins called arteriovenous malformations (AVMs).
Small AVMs, or telangiectases, close to the surface
of skin and mucous membranes often rupture and
bleed after slight trauma. Abbreviated HHT. The
most common manifestations of HHT are recurrent
nosebleeds beginning at about 12 years of age.
About one-fourth of individuals with HHT will
develop gastrointestinal bleeding. Large AVMs may
also bleed in the brain, lung, or other sites. HHT is
inherited as an autosomal dominant trait. Most
patients have a parent with HHT. HHT is unusual in
that it can be caused by a mutation in at least three
different genes. Also known as Osler-Rendu-Weber
syndrome and Rendu-Osler-Weber syndrome.
hereditary multiple exostoses
See 
osteochon-
dromatosis.
hereditary mutation
A gene change that occurs
in a germ cell (an egg or a sperm) and is then
incorporated into every cell in the developing body
of the new organism. Hereditary mutations play a
role in cancer, as, for example, in the eye tumor
retinoblastoma and Wilms’ tumor of the kidney.
Also known as germline mutation.
hereditary spherocytosis
See 
spherocytosis,
hereditary.
heredity
The genetic transmission of characteris-
tics from parent to child.
heritability
The degree to which something is
inherited.
heritable
Capable of being transmitted from par-
ent to child.
Hermansky-Pudlak syndrome
A group of
genetic diseases characterized by a deficiency of
pigment in the skin and eye, a bleeding tendency
resulting from a platelet storage pool deficiency,
and systemic disorders related to deficient function
of lysosomes. Abbreviated HPS. Albinism that
occurs in the eyes results in significant reduction in
visual acuity. Pulmonary fibrosis and granulomatous
colitis are known complications. The diseases are
inherited as an autosomal recessive trait and are
due to multiple different gene mutations. Diagnosis
is made by examining blood platelets under an elec-
tron microscope or by genetic testing. There is cur-
rently no treatment for HPS. Also known as albinism
with hemorrhagic diathesis, pigmented reticuloen-
dithelial cells, and delta-storage pool disease.
hernia
A general term referring to a protrusion
of a tissue through the wall of the cavity in which it
is normally contained. Also known as rupture.
hernia, hiatal
Protrusion of the stomach up into
the opening that is normally occupied by the esoph-
agus in the diaphragm, the muscle that separates the
chest cavity from the abdomen. A hiatal hernia can
be congenital, or it can be acquired through stren-
uous physical activity. Hiatal hernias may contribute
to gastroesophageal reflux disease with associated
symptoms. Treatment involves lifestyle modifica-
tions, medications, and in some cases, surgery. Also
known as hiatus hernia. See also 
gastroesophageal
reflux disease.