C

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Carrier

An individual who carries a single altered gene for a condition. The carrier can pass on the gene to their offspring, who may be affected if they also inherit an altered gene from their other parent. A carrier is a heterozygote for the gene carried.

Carrier testing

Testing to find out if a person who does not show symptoms of a condition nevertheless ‘carries’ a copy of an altered gene which could be passed to his or her children.

Cell

The basic structural unit of all living organisms. A human cell is made up a central nucleus (containing DNA) a cytoplasm and an outer cell membrane.

Child Health Records Department (often referred to as 'child health')

The Child Health Records Department monitors each child who is born. When a mother gives birth the department is notified of the birth. The results of newborn screening tests are also reported to this department.

Chorionic villus sampling (CVS)

An abdominal or cervical procedure performed under continuous ultrasound guidance after 10 completed week in pregnancy to obtain a sample of placental tissue for chromosomal or genetic analysis.  The range of chromosomal and genetic conditions that can be detected is similar to those for amniocentesis. For every 100 women who have this test one will miscarry.

Chromatid

The two identical halves of a chromosome produced as a result of cell division and meiosis.

Chromosomal mosaicism

The presence of two or more cell lines which differ from each other in chromosome number or structure, in an individual that has developed from a single fertilised egg (see Mosaic).

Chromosome

Structures found in the nucleus of cells, composed of DNA and proteins. Normally humans have 46 chromosomes in each cell, 23 from each parent. Of these, 22 are autosomes and one is a sex chromosome.

Chromosome anomaly

A change in the number or arrangement of the normal 23 pairs of chromosomes.

Cochlea

The spiral shaped part of the inner ear where sound it turned from motion of the fluids to electrical impulses in the auditory nerve.

Combined test

Between 11 weeks and 2 days and 14 weeks and 1 day of pregnancy, a combination of the nuchal scan measurement and a blood sample from the mother which measures the concentration of pregnancy associated plasma protein-A (PAPP-A), and free beta human chorionic gonadotrophin (Free beta hCG). Together with the mother’s age and the gestation of the pregnancy, these are used to estimate the chances that the fetus is affected with Down’s syndrome.

Conductive hearing loss

Hearing loss caused by blockage of the external ear or by disorder of the middle ear, resulting in a reduction of sound reaching the inner ear. This can be caused by fluid in the ears which generally resolves itself. Most conductive hearing loss is temporary.

Confirmed result

The results of initial screening tests are not usually 100% certain, and are often called presumptive results. The results of screening tests are NOT confirmed results. They are often confirmed later, with further diagnostic tests.

Congenital

Present at or shortly after birth.

Congenital anomaly

An anomaly present at birth, although not necessarily hereditary.

Congenital dislocation of the hip (CDH)

See developmental dysplasia of the hip.

Congenital hearing loss

Hearing loss considered to be present and detectable using appropriate tests at or very soon after birth.

Congenital hypothyroidism (CHT)

A condition which newborn babies are tested for. People with CHT do not produce thyroid hormones properly. This can affect organ development, in particular the brain. If identified early the baby can be treated and can lead a healthy life. CHT has been screened for throughout the UK since the 1980s.

Cordocentesis

An invasive procedure undertaken from about 18 weeks onwards to obtain a sample of fetal blood from the umbilical cord.  Using an aseptic technique whilst under continuous ultrasound guidance, a sterile needle is passed through the mother's abdomen, uterus, amniotic sac and into the umbilical cord. A small amount of fetal blood is aspirated with a syringe for analysis. A range of tests can be undertaken for example haematological studies, chromosome and genetic analysis. The miscarriage rate is variable depending on the fetal condition and gestational age of the fetus being investigated.

Coverage

This is the proportion of people in the eligible group who actually undergo the screening.

Cut-off level

Screening tests divide people into a group at lower risk of the condition being screened for, and a group at higher risk who are then offered further investigations. Cut off level is a point defined by the programme used to distinguish higher and lower risk.

Cystic fibrosis (CF)

A condition which affects certain organs in the body, especially the lungs and pancreas, by clogging them with sticky mucus. New treatments mean people with CF can live relatively healthy lives. Their quality of life may be improved if the condition is detected and treated in the first months of life. CF is more common in some populations within the UK than others. Some areas have been screening for CF since the 1980s. Within the next few years all newborn babies will be offered screening for the condition.

Cytosine (C)

A nitrogenous base, one member of the base pair G-C (guanine and cytosine) that helps hold together the DNA molecule.