Inheritance means passing of features from one generation to the next generation. The genes of DNA are passed from parent to the child. Any change in the parent DNA will be passed on to their child. Therefore, diseases caused due to change in DNA is called inherited disease or genetic disease.
Cancer occurs due to change in DNA. But it may not be always inherited. First let us see the molecular basis of cancer: DNA damaging agents like virus, radiation and chemicals damages the DNA and usually DNA repair takes place with help of DNA repair gene. The DNAs which fail to get repaired will cause activation of oncogenes, inactivation of tumor suppressor genes and inhibition of apoptosis. This will result in the abnormal cell proliferation and this results in the clonal expansion and thereby cancer.
The damage to the DNA of somatic cells will not be inherited. But mutation to germs cells (sperm or ovum) will pass from generation to generation. This is called germ line mutation.
The gene with mutation which is passed on from the previous generation is called ‘cancer susceptibility gene’ which means being born with a defective gene doesn’t mean that the person will definitely have cancer, but the person will be in a higher risk of developing cancer when compared to others. This is called genetic predisposition to cancer.
Most of the cancers have negative family history and the mutation occurs after birth. These are called sporadic cancer and not hereditary. 90% of the cancers are sporadic. Gene mutations over years in combination with the environmental factors results in cancer. That is the reason why most of the cancer occurs in later ages.
The carcinogenic changes that occur in a cell develops through a series of addition of genetic variations. The main target of mutations is the tumour suppressor gene, p53 or the gene which controls it. p53 is called guardian genome. If p53 is not affected in a cancer then it will have good prognosis (1).
Let us see some of the mutated genes and associated cancer (2):
1. BRCA gene: Mutation of BRCA gene causes breast cancer and ovarian cancer in females and prostate cancer in males.
2. PTEN gene: Breast and uterine cancer in females. Thyroid cancer in both females and males.
3. APC gene: Colorectal cancer and soft tissue tumours.
4. Tp53 gene: Soft tissue sarcomas, breast cancer, leukaemia, lung cancer, brain tumour.
5. MEN1 gene: Cancers of endocrine system.
6. VHL gene: Hemangioblastomas, angiomas.
When a person have strong family history of cancer, it means that many of their relatives were diagnosed with the cancer over several generations. In such cases this person is of higher risk of developing a cancer. Genetic testing, specialist consultation and risk assessment may help in such cases (3)
Gene therapy can be used as the treatment modality for cancer by incorporating a healthy gene to restore the lost function or add a new function. This can be done using a vector such as inactivated virus. Effect of gene therapy done on somatic cells will not be inherited while the effect of gene therapy done on germ cells will be inherited to the next generation.
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