Introduction to Genetic Testing

Genetic tests examine DNA, the chemical in our cells which provides our bodies with instructions about how to grow, develop and function. DNA is composed of two strands of four nucleotide bases, or “letters” (Adenosine (A), Thymine (T), Guanine (G), Cytosine(C)), arranged in a particular order. Each gene produces a specific protein, determined by the order of these bases. Humans have ~25,000 different genes, arranged on a number of thread-like structures, called chromosomes. We inherit our chromosomes from our parents, 23 from our mother and 23 from our father, so we have two sets of 23 chromosomes, or 23 ‘pairs’. A good description is if you think of genetics as the book of life, then the DNA are the letters, the genes are words, and the chromosomes are the chapters.

Often times, people living with the same inherited retinal disease (IRD), for example Retinitis Pigmentosa (RP) have varying mutations in the same genes or different mutations in different genes which causes the condition. Genetic testing allows for these specific mutations to be identified and can influence the health care and management of the individuals with these conditions into the future.

A mutation occurs when one or more of these bases are replaced by another base-pair. Some mutations don’t change the type of protein produced (synonymous mutation) and everything continues to function as normal. Other mutations called non-synonymous mutations alter the protein produced and can have a negative impact on how our bodies function. If you think of a mutation as a spelling mistake or a series of words changed in a sentence, then this causes a problem in the meaning and the sentence no longer makes sense. Retinal conditions caused by a genetic mutation are called inherited retinal diseases (IRDs).

A genetic test takes the form of a blood or tissue sample (mouth swab) that is analysed in a laboratory by scientists and can identify which gene or chromosome abnormality is causing a particular condition in an individual or family. The results of a genetic test are incredibly important and helpful for health care providers as they can accurately advise patients about how their condition is likely to progress and provide more clarity about how these rare eye diseases (REDs) are inherited.

Genetic testing also plays a big role in assisting the researchers to better understand disease pathways in the hope that it will help progress clinical research and develop appropriate treatment for these REDs and IRDs. But most importantly, genetic testing allows patients and their families to better understand their condition, empowering them with the knowledge to make informed decisions regarding their healthcare and life choices.

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