Genetic and Medical Glossary

Glossary

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There are 57 names in this directory beginning with the letter H.
Hair whorl, abnormal number
more than two clockwise hair whorls

Hair whorl, abnormal position
hair growth from a single point on the scalp in any location other than lateral to the midline and close to the vertex of the skull

Hair, frontal upsweep
upward and/or sideward growth of anterior hair (cowlick)

Hallucination
Subjectively experienced sensations or false sensory perception in the absence of an appropriate stimulus, but which are regarded by the individual as real

Hamartoma
benign tumor-like malformation resulting from faulty development in an organ and composed of an abnormal mixture of tissue elements that develop and grow at the same rate as normal elements but are not likely to compress adjacent tissue

Hand–foot–genital syndrome
condition that affects the development of the hands and feet, the urinary tract, and the reproductive system; caused by mutations in the HOXA13 gene in chromosome 7 at 7p15.2

Haploid
refers to a cell or an organism with one set of chromosomes

Haploinsufficiency
refers to a protein produced by a single gene copy which is then insufficient for normal functioning, leading to an abnormal or diseased state; responsible for some but not all autosomal dominant disorders

Hemifacial microstomia
congenital disorder that affects the development of the lower half of the face, most commonly the ears, the mouth and the mandible

Hemihypertrophy
condition in which one side of the body or a part of one side is larger than the other

Hemivertebrae
congenital anomaly of the spine that is characterized by the formation of half of a vertebral body, a corresponding pedicle, and a corresponding hemilamina

Heredity
the overall mechanism by which characteristics or traits are passed from one generation of organisms to the next; genetics is the scientific study of heredity

Heterochromia irides
difference in color between the irises of the two eyes

Heterogeneous
not uniform in structure or composition; phenomenon in which a single phenotype or genetic disorder may be caused by any one of a multiple number of alleles or non-allele (locus) mutations

Heterotaxy
abnormality where the internal thoraco-abdominal organs demonstrate abnormal arrangement across the left-right axis of the body

Heterotopia
clusters of neurons placed in unusual places along the lateral ventricles

Heterozygote
an individual with two different alleles at a gene locus (site)

Heterozygous
composed of two alleles that are different

Hexadactyly
presence of an extra digit (ie, a sixth finger or toe)

Hippocampus
elongated ridges on the floor of each lateral ventricle of the brain, thought to be the center of emotion, memory, and the autonomic nervous system

Hirschsprung’s disease
characterized by the absence of particular nerve cells (ganglions) in a segment of the bowel, causing muscles to lose their ability to move the stool through the intestine (peristalsis) and resulting in constipation and obstruction of the colon

Hirsutism
excessive growth of facial or body hair in women

Histone
specialized protein in eukaryotic cells that binds to DNA molecules and causes them to become more compact; also thought to be involved in regulation of gene expression

Holoprosencephaly (HPE)
failure of the forebrain (prosencephalon) to develop normally; instead of the normal complete separation of the left and right halves of the forebrain, there is an abnormal continuity between the two sides; alobar HPE is the most severe form

Homologous
refers to chromosomes that are identical in terms of types of genes present and the location of the centromere

Homozygote
an individual with two identical alleles at a gene locus (site)

Homozygous
characterized by a genotype composed of two alleles that are the same and at the same locus

Horseshoe kidney
congenital partial fusion of the kidneys resulting in a horseshoe shape

Human Genome Project
multiyear genetic research endeavor that sequenced the entire human genome; officially completed in 2003

Hunter–McAlpine syndrome
dominantly inherited syndrome characterized mainly by premature fusion of skull bones, mental retardation, small mouth, short stature and finger and toe anomalies; thought to be caused by duplication of the region 5q35-qter on chromosome 5

Hybridization
a process of base pairing involving two single-stranded nucleic acid molecules with complementary sequences; the extent to which two unrelated nucleic acid molecules will hybridize is often used as a way to determine the amount of similarity between the sequences of the two molecules

Hydrocephalus
condition in which abnormally widened (dilated) cerebral spaces in the brain (ventricles) inhibit the normal flow of cerebrospinal fluid (CSF), resulting in accumulation of cerebrospinal fluid (CSF) in the skull which puts pressure on the brain tissue; treatment involves insertion of a shunt to redirect the CSF for elimination, usually through the stomach

Hydrocolpos
accumulation of mucus or other non- sanguineous fluid in the vagina

Hydronephrosis
distention of the kidney with urine; caused by obstruction of urine outflow

Hygroma
sac, cyst, or bursa distended with a fluid

Hyperacusia
over-sensitivity to loud noises

Hypercalcemia
abnormally high level of calcium in the blood, usually more than 10.5 milligrams per deciliter of blood

Hyperopia
condition of the eye where incoming rays of light reach the retina before they converge into a focused image

Hyperphagia
over–eating, sometimes with insatiable appetite

Hyperpigmentation
darkening of an area of skin or nails caused by increased melanin

Hypertelorism
abnormally increased distance between two organs or parts; usually refers to the eyes

Hyperthyroidism
over active thyroid gland

Hypertrichosis
abnormal amount of hair growth over the body

Hypodontia
congenital condition marked by a less than normal number of teeth

Hypogonadotropic-hypogonadism
pubertal failure similar to Kallman syndrome, but with a normal sense of smell; due to deficiency of the reproductive hormone gonadotropin-releasing hormone

Hypomelanosis of Ito
not a specific entity but rather represents features of many different forms of mosaicism; characterized by unilateral or bilateral hypopigmented macules in whorls, streaks, and patches in a “marble-cake” pattern, variably associated with epidermal nevi, alopecia, and ocular, skeletal, and neural abnormalities

Hypoparathyroidism
Underfunctioning of the parathyroid glands with deficient production of the hormone parathormone which leads to low blood calcium

Hypoparathyroidism, deafness, renal syndrome
autosomal dominant disorder characterized by hypoparathyroidism, sensorineural deafness, and renal disease caused by mutation of the GATA3 gene located on chromosome 10 at 10p15

Hypopigmentation
diminished pigmentation in a bodily part or tissue

Hypoplasia
incomplete development or underdevelopment of an organ or tissue

Hypoplastic
abnormal deficiency of cells or structural elements

Hypoplastic left heart syndrome
form of congenital heart disease in which the whole left half of the heart (including the aorta, aortic valve, left ventricle and mitral valve) is underdeveloped (hypoplastic)

Hypoplastic supraorbital ridges
Flatness of the supraorbital portion of the frontal bones (brow area)

Hypospadias
developmental anomaly of the urethra in which a part of the urethral canal is open on the undersurface of the penis or on the perineum

Hypotelorism
abnormally decreased distance between two organs or parts. Usually refers to the eyes

Hypothyroidism
underactive or inactive thyroid gland

Hypotonia
floppiness, low or underdeveloped muscle tone

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