By far and large, all of us are products of gene lottery: our individual genome – the genetic blueprint that mapped, among others, our future health or ill-health – is the result of random mixing and swapping of our parents’ genes, which of course they inherited individually from a long line of forbearers. This is a lottery for two reasons: one, the shuffling of our parents’ genes when they made the egg or sperm respectively, and the mosaic genotypes that resulted in us when the sperm fertilised the egg; and two, dad did not choose his mate based on what he knew about her genetic fitness or suitability, and mom, likewise. Most of the time, happily, most of us get a reasonably good draw of genetic cards and thus are relatively healthy; many, though, are shuffled a bad hand, and some even suffer horribly from genetically-inherited diseases such as cystic fibrosis, breast cancer, thalassemia , sickle-cell anemia, and many more. In fact, there are hundreds of diseases, perhaps thousands, are now known to be caused by defects in genes, often a single misspelling in the genetic code.
There is a married couple who are very close relatives of mine who have a gut-wrenching story to tell. Having just been married, they were eager to start a family. It was a joy to see them, like all proud parents, dotting on their first-born. 5 months later they buried their little son. Then in quick succession they tried to have children to ameliorate their loss. The second-born died as a 3-month old while the third lasted 8 months as the doctors and parents battled and tried their best to save him from the same fate as his siblings. The doctors said their little hearts did not grow even as their bodies grew. I never did know the technical terms by which the doctors characterised the disease but it is obvious they suffered from congenital heart defects. Perhaps, it was like Ellis-van Creveld syndrome, a form of congenital heart defect that is a rare autosomal recessive trait. Perhaps with one sick child you can reasonably suspect an aberrant genetic mutation but 3 sick children in succession point to a genetic inheritance with deep (and fatal) penetrance.
Alice Wexler’s book, The Woman Who Walked into the Sea: Huntington’s and the Making of a Genetic Disease chronicles the history of one of the most dreaded of inherited diseases, Huntington’s, which is a disease that causes an progressive, unrelenting movement disorder with progressive mental decline and death.
Alice Wexler is also the sister to Nancy Wexler who was part of the team who spent more than 2 decades to track down the gene involved (at the tip of Chromosome 4, by the way) and causing Huntington’s Disease. Both of them, being the daughters of a woman afflicted with the disease, have a 50% chance of inheriting the affliction.
If you are interested in how your genes may and can define you, including how these may affect your future health, and how you may bequeath your kids with “bad” or “good” genes, I can give no better recommendation than Matt Ridley’s Genome: The Autobiography of a Species in 23 Chapters (P.S.). There are more indepth books of course, but Ridley writes succinctly for the non-scientific ilk like us.