Medical terms are usually formed of a number of parts which include a root, a prefix and/or a suffix. Knowledge of how terms are built up help in the understanding of medical terminology. For example, hyper- means excessive or increased and hypo- means deficient or decreased thus hypertension is higher than normal blood pressure and hypotension is lower than normal blood pressure.
General medical dictionaries
Web: http://www.childrenfirst.nhs.uk/kids/hospital/dictionary. Clear descriptions of range of medical terms for children and parents.
Web: http://www.nelh.nhs.uk/directories.asp
Detailed explanation of medical terms available at the UK National electronic Library for Health (NeLH).
Web: http://www.nlm.nih.gov/medlineplus/mplusdictionary.html
Short explanation of medical terms from the US government MedlinePlus.
Genetic glossaries and information
Web: http://www.genome.gov/glossary.cfm
US National Institute of Health (NIH) Glossary of Genetic Terms.
Web: http://www.gig.org.uk/education.htm
Genetic glossary and explanation of inheritance modes.
Glossary of medical terms used
ABNORMAL
A variation from the normal. In the case of genes an abnormal gene may result in a specific disorder.
ACQUIRED
A condition or disease originating after birth. An acquired condition is not hereditary.
ACUTE
A sudden onset of symptoms or disease which may be severe and/or brief in duration.
AUTOSOMAL
Something which pertains to the autosome which is any chromosome other than the X and Y (set chromosomes). In practice it means that the abnormal gene can affect males or females equally.
AUTOSOMAL DOMINANT
Where an individual possesses an altered gene that individual will demonstrate characteristics of the disorder. The condition will be transmitted to children with a 50 per cent chance of an affected child for each pregnancy.
AUTOSOMAL RECESSIVE
Where an individual carries an altered gene this will not affect the individual him or herself. However, when two carriers of the same altered gene have children there is a 25 per cent chance of an affected child for each pregnancy.
BALANCED TRANSLOCATION
Occurs when two chromosomes break and exchange places leaving the same amount of genetic material. An individual with a balanced translocation will be unaffected, but children may be affected in a variety of ways.
CARRIER
An individual who carries the abnormal gene for a specific condition without symptoms (also referred to as heterozygote).
CATHETER
A tube used either for withdrawing fluid from a body cavity or for introducing fluid to a body cavity.
CELL
The basic structural unit of all living organisms. It is surrounded by a membrane and contains a nucleus which carries genetic material.
CHORIONIC VILLUS SAMPLING
A method of collecting the chorion cells from the pregnant mother. Chorion cells are situated on the wall of the uterus (womb). They have the same origin as the fetal cells and can, therefore, be analysed to detect certain fetal abnormalities in the fetus.
CHROMATID
The two halves into which a chromosome is longitudinally divided at mitosis and meiosis.
CHROMOSOME
A rod like structure present in the nucleus of all body cells (with the exception of the red blood cells) which stores genetic information. Normally, humans have 23 pairs, the unfertilised ova and each sperm carrying a set of 23 chromosomes. On fertilisation the chromosomes combine to give a total of 46 (23 pairs).
CHRONIC
Long-term or prolonged disease or condition which can persists or progresses over a long period of time.
CONGENITAL
A condition which is present at birth, although it can be recognised prenatally, at birth or many years later. A Congenital disorder can be genetic or acquired at any time during fetal development.
DELETION
The absence of genetic material on a chromosome.
DIZYGOTIC
Two cells having been fertilised resulting in twins.
DNA
Deoxyribonucleic acid is the 'building block' for all genetic material.
DUPLICATION
Occurs where a chromosome or part of a chromosome is duplicated. This may happen during cell division prior to fertilisation.
ENZYME
A protein substance which is essential to the correct functioning of biochemical reactions which break down food into essential chemicals required by the body and/or break down toxic by-products in our bodies.
FAMILIAL
Characteristic of some or all members of a family.
FETOSCOPY
Method of prenatal diagnosis where the inside of womb and the developing fetus can be examined visually and sampling can be performed using a fetoscope.
FRAGILE SITE
A site on a chromosome where genetic material may be prone to break. In Fragile X syndrome there is a fragile site on the female X chromosome.
GENETIC COUNSELLING
Information and support provided by a specialist doctor, usually a geneticist, to parents who have known conditions in their families or who are concerned about the future possibility of genetically transmitted conditions.
IDIOPATHIC
A disease or syndrome that is of unknown cause.
IMPRINTING
Refers to the phenomenon whereby the effect of inheriting a gene is different depending on whether the inheritance was from the mother or father e.g. Prader Willi syndrome and Angelman syndrome.
INVERSION
Occurs where a chromosome breaks in two and becomes reattached after turning round 180 degrees. Providing no chromosome material is lost, this abnormality should have no effect on the individual. However, that individual may carry the risk of producing eggs or sperm with the incorrect amount of chromosome material.
HOMOZYGOTE
A homozygote has a double dose of an altered gene as in an affected individual with an autosomal recessive disorder.
MEIOSIS
The process of cell division which results in a cell where the 23 pairs of chromosomes split into two, each with 23 chromosomes. These cells are the female ova (eggs) and the male sperm.
MITOCHONDRIA
Refers to the small bodies which are responsible for energy production and also carry their own genes and DNA.
MITOSIS
Division of all cells except the reproductive cells with chromosome numbers and genetic make-up identical to that of the parent cell.
MONOSOMY
The total loss of one of a pair of chromosomes. This occurs, for example, in Turner syndrome where one X chromosome is lost leaving a total of 45 chromosomes.
MOSAICISM
Where a genetic or chromosomal abnormality does not occur in all body cells. The proportion of normal to abnormal cells will determine the severity of the disorder.
MUTANT
A gene which has undergone change from the normal gene. This mutation may be an established one or a new sporadic mutation.
NEURAL TUBE DEFECT
Occurs when there is a defective development of the spinal cord and the brain. Conditions such as Spina Bifida and Anencephaly (absent brain) are examples of such developmental defects.
NUCLEUS
Portion in the centre of each cell which contains the chromosomes with their genetic material.
OVUM
Female egg: reproductive cell carrying 23 chromosomes.
PENETRANCE
The degree to which an individual who carries a dominant gene may show symptoms of the disorder.
PLACENTA
A complex structure occurring in pregnancy. It is attached to the wall of the womb and connected to the fetus by the umbilical cord. The fetus receives its nourishment through the placenta and the vessels of the umbilical cord.
PREDISPOSITION (GENETIC)
That the individual concerned is intrinsically more prone to develop a particular disorder.
RING FORMATION
Occurs where the ends of a chromosome bend over and fuse together with a loss of genetic material.
ROBERTSONIAN TRANSLOCATION
Occurs when translocations of chromosomes involve end to end fusion with the loss of the short arms. The balanced carrier has 45 chromosomes and is normal, any children may be affected in number of ways.
SPERM (abbreviation of spermatozoon)
The male reproductive cell carrying 23 chromosomes.
STATUS MODE (PATTERN OF INHERITANCE)
Describes how the gene is inherited: for example, autosomal dominant, autosomal recessive or X-linked.
TRANSLOCATION
Occurs where there is a rearrangement in which a piece of one chromosome is transferred to another with a different number.
TRIPLOIDY
The presence of a full extra set of chromosomes. This abnormality is invariably lethal and would lead to a miscarriage or stillbirth.
TRISOMY
The addition of a complete extra chromosome to a pair.
TWINS
May be genetically identical (monozygous) when they arise from a single fertilised egg or non-identical (dizygous) when they arise from two separate eggs.
X-LINKED RECESSIVE
The form of inheritance where the abnormal gene is carried on the X chromosome. It is a form of inheritance where girls are usually carriers and boys are affected. This is because the male Y chromosome does not carry the compensatory normal gene.
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