Misconceptions around Hereditary Diseases

When it comes to little Vedant having his maternal grandmother’s perfectly-chiselled nose or his dad’s dark curly hair, the similarities lead us to conclude that these features were inherited or hereditary. But when it comes to diseases, the conclusions may not be as straightforward. It is common to hear doctors asking us about our family history. And that’s completely justified as it could give them hints about what kinds of conditions we are more likely to end up with. But the extent of this likelihood as well as which specific conditions, is far from determined merely by the fact that these diseases ‘run in the family’.
Studies on various types of non-communicable diseases (very broadly understood as diseases that do not spread through contact with other people or discharges from the infected person that are present in the air, water or food or transmitted through vectors) are constantly churning out new and interesting findings and these sometimes contradict what was formerly held as ascertained. So, for instance, some studies have found that leukaemia – a cancer of the blood or bone marrow – is not really an inherited disease, although the tendency to develop cancers appears to be hereditary to some extent.
There are other diseases that are genetic, in the sense that they occur due to the genetic structure that a person possess, but they do not really run in families at all. For instance, Down syndrome, a condition that some babies are born with due to a defective gene, occurs completely randomly. To put it very simplistically, the occurrence of such genetic diseases can be explained as errors that take place while genes are being copied from parents to children.
Then there are also diseases that do have a basis in hereditary but the pattern of inheritance is complicated. If we take the case of a mental illness called schizophrenia, studies broadly suggest that there is a 1% chance of anyone in the population developing schizophrenia but having a close relative with the disease increases the chances to 10%. They also surmise that having a distant relative with schizophrenia increases the chances of developing it to over 1% but the chances are lower than the 10% attributed to those with close relatives.
In some other cases, despite the above average occurrence of a particular type of disease in a family, the risk of everyone in that family of getting the disease does not increase above average levels for the population in general. So, for instance, if a family is dotted with cases of cancers of various types (lung, breast, blood, etc) or cardio vascular diseases of various types (high blood pressure, coronary artery disease, strokes, etc) it does not necessarily mean that everyone in that family has a higher chance of developing cancers or cardio vascular diseases, respectively.
On the flip side, there is a lot of research which points to the fact that in a number of diseases that are thought to be hereditary, simply possessing the gene which is susceptible to a particular disease does not necessarily mean that one will fall prey to it with certainty; there are some environmental triggers, or the lack of them, which result in the disease never manifesting.
In a nutshell, there are still many grey areas around the hereditary nature of diseases. But it is always recommend that we prepare for the worst and home for the best. There is no disputing the fact that early detection and the most appropriate course of medical action can intervene towards ameliorating, slowing or stemming the progress of a number of conditions.
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