The information provided here is intended for patients who use our services, people who may need to use our services in the future and anyone wanting to find out more about genomic testing in the NHS.

Genomic medicine refers to the study of an individual's genetic makeup to identify the cause of their condition or susceptibility. By combining and analysing information about patient genomes, with other clinical and diagnostic information, patterns can be identified that can be used to diagnose a condition, predict and prevent disease, and determine the most effective interventions to help improve patient health.

Our team collaborates with genomic laboratories, clinicians and researchers to deliver the benefits of genomic medicine to patients, families and healthcare professionals across North West London.

The video below explains what DNA is and how understanding the properties of our DNA is essential for genetic and genomic testing.  


Genomics vs genetics

Genomics vs genetics diagram

How is a genome sequenced?

Collecting DNA

Patients who took part in the 100,000 genomes project donated a sample of their DNA, mainly in the form of a blood sample. Cancer patients also donated a tumour sample.


There are a variety of methods and machines that can be used to sequence genomes. DNA sequencing machines can’t sequence the whole genome in one go, they sequence the genome in short pieces, each piece is referred to as a ‘read’.


The reads from the sequencing machine are matched to a ‘reference genome sequence’. This is done by mapping software on high performance computers. The software finds where each read belongs on the genome.


Each individual has many differences to the reference sequence. These differences are known as variants. Most of the differences are completely harmless – they are the reason we are different from each other. However, some differences can be disease causing. The findings and any implications are discussed with the patient.

How do you sequence infographic

Why have genomic testing?

A healthcare professional may order a genomic test for several reasons:

Diagnostic testing – to confirm a diagnosis of a particular cancer or rare disease

  • when you display relative symptoms – ‘clinical presentation’
  • a yes/no test
  • can be used to confirm an initial diagnosis or alternatively to rule out a possible cause of the symptoms.

Clinical predictive testing – to assess your risks of developing a genetic condition and to guide preventative care

  • before you display any symptoms
  • usually when a family member has been diagnosed with a genetic condition
  • for a gene that is associated with a condition that is ‘actionable’ – it can be treated or the risk can be reduced with lifestyle changes and/or regular screening
  • for a condition that is not actionable but is sufficiently severe that you may want to know about it before making major life decision (such as starting a family).

Tumour testing – to identify gene mutations present in the tumour cells that are either actionable (meaning targeted treatment can be offered), or warrant further study. This involves comparing the genomes of a patient’s tumour cells with those of the patient’s healthy cells. This can also help in identifying genes that are actionable in other ways, e.g. identify new research targets such as genes that are seen to be ‘driving’ cancers to develop and spread.