Genome
The term genome is used to describe the genetic material of an organism. In humans it consists of DNA, RNA. It includes the genes and the non-coding DNA. Please see definitions below.
Genomics
This refers to the branch of molecular biology concerned with the structure, function, evolution, and mapping of genomes.
The 100 000 Genomes project
The aim of this project is to create a new genomic medicine service for the NHS. Further information can be found on the Genomics England website. www.genomicsengland.co.uk
Genes
Genes are segments of DNA that provide templates (or patterns) for the manufacture of proteins. Mutations or mistakes in a particular gene can mean that the protein that is made will not function properly or will not be made at all, and this can cause disease.
Since the first genes causing NCL were identified in 1995 over 400 mutations or mistakes in 14 different genes have been discovered. These 14 genes encode or are responsible for the production of different proteins.
Chromosomes
Genes are organized and packaged within the cell in structures called “chromosomes.” Humans have 23 pairs of chromosomes. A child will inherit a set of chromosomes; one chromosome comes from their mother, and the other from their father.
Genetic Code
Each gene is composed of a series of letters adenine (A), thymine (T), guanine (G) and cytosine (C), which correspond to the different bases in the DNA, the sequence of which forms the genetic code.
DNA (deoxyribonucleic acid)
DNA is a molecule found in the nucleus of every cell that holds the template for how living organisms are built and all the proteins we need to make to be healthy. It is made up of chemical building blocks and the order, or sequence, of these determines what biological instructions are contained in a strand of DNA.
RNA
RNA stands for ribonucleic acid. It is an important molecule with long chains of nucleotides. The main function of RNA is to carry information from the genes to where proteins are assembled on ribosomes in the cytoplasm. This is done by messenger RNA (mRNA).
Proteins
Proteins are large, complex molecules that play many critical roles in the body. They do most of the work in cells and are required for the structure, function, and regulation of the body’s tissues and organs.
Proteins are made up of hundreds or thousands of smaller units called amino acids, which are attached to one another in long chains. There are 20 different types of amino acids that can be combined to make a protein. The sequence of amino acids determines each protein’s unique 3-dimensional structure and its specific function.
Genetic Diagnosis in the NCLs
Genetic testing can be used to find out whether a child or young person has specific genetic mutation or mistake in a particular NCL gene.
Blood or cell samples will need to be taken sent to be tested, and examined in a genetics laboratory to check for mutations in the specific NCL gene.
This can be a complex process and samples may be sent to specialist centres for analysis. This means that this may take time, and it is not always possible to give definite answers after genetic testing.
Diagnostic Reports
Once all of the evidence has been gathered, a report detailing the findings is produced, concluding whether the diagnosis has been confirmed or not. This will be sent to the clinician who has made the referral and who will discuss the results with the family.
This report will usually contain the following information:
- Referral Reason – this explains the test that is being performed, why this has been requested, and includes any clinical and biochemical information that supports the diagnosis.
- Results – this is a table that details the mutations that have been found in the patient using the DNA numbering.
The NCLs are autosomal recessive disorders as explained in the leaflet, the genetic test will be looking for the mistakes in each of the 2 chromosomes, one inherited from each parent.
- Report – this goes into more detail about what has been found and what evidence has been used to reach the conclusion. This can be difficult to interpret and an appointment should always be available for the results to be explained by a qualified professional.
Carrier Screening
Essentially the same scientific process, which is used for Genetic Diagnosis, is also used to obtain results for Carrier Testing or Screening. When a diagnosis of NCL is confirmed or suspected other family members may wish to be tested to see if they also carry the same mutation.
A referral will be needed by a GP or Consultant and this should be to the local genetic counselling service and for samples to be sent for analysis. This service should also provide support and advice in understanding and interpreting the results.