Glossary of terms used on this site

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(sickle-cell) crisis

Sickle cell crisis (episodes of pain): Episodes of pain during a sickle cell crisis are one of the most common and upsetting symptoms of sickle cell anaemia.

A sickle cell crisis is triggered when the abnormal blood cells block the small blood vessels that supply the body’s tissue. This causes the cells in the affected tissue to start dying, resulting in swelling which irritates nearby nerve endings.


47, XXY is the way in which the karyotype of a person with Klinefelter syndrome is written. It contains information on the total number of chromosomes present as well as the sex chromosomes. Most men with KS have an extra copy of the X chromosome (47, XXY) instead of the more usual 46 chromosomes that include one X and one Y chromosome (46,XY).

This occurs as a random error during cell division to create either the egg or sperm. The chromosomes fail to separate correctly and the egg or sperm gains an extra copy of the X chromosome.

50% risk

Risk: The probability that a particular family member will be affected by a genetic disorder which has occurred in the family.

With autosomal dominant FAP there is a 50 percent chance of passing the mutated gene to each child. The chance that a child will not inherit the mutated gene is also 50 percent.



An abscess is a collection of pus which can occur in almost any part of the body, treated with antibiotics and drainage.


Briefly losing awareness of surroundings, possibly several times a day. Absences mainly affect children but can occur in adults.


Achondroplasia is a disorder of bone growth, whereby the cartilage fails to convert into bone, particularly in the long bones of the arms and legs. All people with achondroplasia have short stature. It is inherited in an autosomal dominant pattern.


A non-cancerous tumour.


A behaviour disorder originating in childhood in which the essential features are signs of developmentally inappropriate inattention, impulsivity, and hyperactivity.


(ALD) X-linked adrenoleukodystrophy is a disorder that occurs most often in males. It mainly affects the nervous system and the adrenal glands, which are small glands located on top of each kidney. People with this disorder often have progressive destruction of the fatty covering (myelin) that insulates nerves in the brain and spinal cord. They may also have a shortage of certain hormones caused by damage to the outer layer of the adrenal glands (adrenal cortex). This hormonal deficiency is known as adrenocortical insufficiency.

There are three distinct types of X-linked adrenoleukodystrophy: a childhood cerebral form, an adrenomyeloneuropathy type, and a type called Addison disease only.

Adrenoleukodystrophy (ALD)

X-linked adrenoleukodystrophy is a disorder that occurs most often in males. It mainly affects the nervous system and the adrenal glands, which are small glands located on top of each kidney.

Ajmaline test

(provocation test) You may be asked to have this test if your doctor suspects Brugada Syndrome. While you are having an ECG test you will be given an injection of ajmaline or flecainide (antiarrhythmic drugs). The test may show changes on the ECG that are typical of one of the channelopathies.


An inherited condition that causes urine to turn black when exposed to air. Ochronosis, a build-up of dark pigment in connective tissues such as cartilage and skin, is also characteristic of the disorder. People with alkaptonuria typically develop arthritis in adulthood, particularly in the spine and large joints.

Alkaptonuria is caused by changes in the HDG gene which makes an enzyme that helps break down the amino acids phenylalanine and tyrosine. Alkaptonuria is inherited in an autosomal recessive pattern.


Alternative forms of a gene at the same locus (position on a chromosome)

Alternative medicine

Complementary medicines and treatments include a wide range of treatments that are not usually used by most doctors in the UK. These treatments are sometimes described as alternative medicine.


Abbreviated form of the term amniocentesis. A procedure whereby a needle is introduced through the abdominal wall and into the pregnant uterus to obtain amniotic fluid. The procedure is most commonly used to obtain fetal cells to examine the fetal chromosomes or occasionally fetal DNA. The procedure is usually carried out at 16 weeks gestation

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