The Leeds Teaching Hospitals NHS Trust

Constitutional Cytogenetics

Introduction to Cytogenetics

Cytogenetics is the study of chromosomes and chromosomal abnormalities. The normal number of chromosomes in a human cell is 46. Chromosomes are made from DNA, and contain all the genes present in a cell. Each gene is located at a specific site on each chromosome. There are many clinical syndromes that have been associated with particular chromosomal abnormalities. The image below shows a normal male chromosome complement.


Chromosomal abnormalities usually involve large amounts of DNA and therefore tend to involve large numbers of genes. For this reason, disorders associated with chromosomal abnormalities are usually very serious and can involve multiple organs. Often these abnormalities are severe enough to be fatal, either in utero or in early life.
Each normal human cell contains 23 pairs of chromosomes. 22 of these pairs are identical, the other constitutes the sex chromosomes (one X and one Y in a male and two Xs in a female).

The largest chromosome in the human complement is numbered '1' and the smallest '22'. Modern techniques within the laboratory allow the chromosomes to be identified from one another by distinguishing bands on the chromosomes.

The work of the department can be broken down into the following main areas.

Blood culture and karyotyping

This category comprises the major part of the workload. Urgent samples include those from newborn babies and pregnant women and their partners. Non-urgent referrals include patients with a history of infertility, individuals with impaired physical or sexual development, patients with a family history of a known chromosome abnormality, follow-up from prenatal diagnosis (confirmation of abnormal prenatal results only), screening of patients and donors for IVF and patients with a suspected chromosome fragility syndrome.

SNP array

SNP array is provided as a first line for test for patients for paediatric patients with learning difficulties, behavioural problems, developmental delay, autism, seizures and/or dysmorphism. Newborns may also be tested with congenital abnormalities at the clinicians request. Professional judgment will be used to determine which patients are tested in line with current laboratory policy.

Prenatal Diagnosis

Prenatal diagnosis is carried out by one of three methods - chorionic villus biopsy, amniocentesis or fetal blood sampling. Indications for prenatal diagnosis include advanced maternal age, problems detected on ultrasound scan, risks identified through measuring biochemical markers, and the presence of a family history of a chromosome abnormality. The main abnormality detected is Down Syndrome.

Solid Tissues

Since up to 50% of all spontaneous abortions may have a chromosome abnormality, products of conception after a pregancy loss may be referred for chromosome analysis. Skin biopsies from living persons are also occasionally received either for cytogenetic analysis or for referral onwards for biochemical testing or DNA studies.

Hospitals we receive frequent referrals from:

Northallerton, Scarborough, Hull, Scunthorpe, Grimsby, Pontefract, Wakefield, Calderdale, Airedale, Harrogate, York, Leeds General Infirmary, St James's Hospital, Bradford, Dewsbury. Although we are happy to receive referrals from any hospital.