Some diseases are written in the genome. Pathological genetics is the study of how changes in DNA — inherited or acquired — cause disease, and it has moved from a niche specialty to something central to modern medicine as genetic testing and targeted therapies have matured.
Types of genetic change
Disease-causing changes range from the tiny to the wholesale: point mutations (a single DNA letter altered), insertions and deletions, and large-scale chromosomal abnormalities (extra, missing, or rearranged chromosomes). Whether a change causes disease depends on what it does to the protein the gene encodes — or to gene regulation.
Patterns of inheritance
- Single-gene (Mendelian) disorders — caused by one faulty gene, inherited in recognisable patterns (dominant, recessive, X-linked). Examples include cystic fibrosis and sickle-cell disease.
- Chromosomal disorders — from whole-chromosome changes, such as the extra chromosome 21 in Down syndrome.
- Multifactorial / polygenic — many genes plus environment, behind common conditions like heart disease and diabetes. Most disease risk is of this kind, not single-gene.
Most disease isn't 'a gene for X' — it's many genetic influences interacting with environment. The single-gene cases are the exception that taught us the rules.
Cancer is a genetic disease
Cancer is fundamentally a disease of the genome — an accumulation of mutations that unleash cell growth. Two gene classes are central: oncogenes (accelerators stuck on) and tumour-suppressor genes (brakes that have failed). Understanding which are altered in a given cancer increasingly guides targeted treatment.
Why it matters clinically
Genetic understanding now drives diagnosis (genetic testing), risk prediction (knowing a patient's inherited risk), reproductive counselling, and a growing wave of targeted and personalised therapies aimed at the specific molecular fault. Pathological genetics is where the future of precision medicine is being built.
Decode the genetics of disease
My Pathological Genetics course covers mutation types, inheritance patterns, chromosomal disorders, and cancer genetics — how DNA changes become clinical disease.
View the course →Questions
Is most disease caused by single genes?
No — most common disease is multifactorial (many genes plus environment). Single-gene disorders are important but relatively rare; they taught us the principles.
Is cancer genetic?
Yes — cancer is fundamentally a disease of accumulated genetic changes, typically activating oncogenes and disabling tumour-suppressor genes, though most cancers aren't inherited.