Odd gene

My Marfan Tale — Part 3

Xem bản dịch tiếng Việt/ For Vietnamese, please see: Gien dở hơi.

  1. Dislocated lenses (My Marfan Tale — Part 1)
  2. Broken heart (My Marfan Tale — Part 2)
  3. Odd gene

I teach General Genetics every year. My students are young and bright sophomores determined to become doctors. After the first three weeks, I would camouflage my story in a question and let them play doctor.

“Emily is an eight year old girl who has recently been diagnosed with Marfan syndrome. Marfan syndrome is a dominant genetic disorder caused by mutations in genes that code for connective tissue proteins such as fibrillin or collagen. The typical signs of this syndrome are tall and lanky build, dislocated lenses, flexible joints, and lungs problems. Emily has all of these signs.

In patients with Marfan, the aorta may become enlarged and ruptured, which is extremely dangerous and potentially fatal (40% of Marfan patients will die immediately if aorta dissection occurs, the risk of death is between 1% to 3% per hour after the dissection event). Patients should avoid demanding physical activities and contact sports to avoid putting extra strain on the aorta and the heart. Aorta abnormality can be detected early by regular echocardiograms. A drug called Losartan can slow down aorta growth rate. If necessary, surgeries can be indicated prior to aorta dissection event and can decrease the risk of death to less than 2%.

Your medical team consisting of a family physician, a genetic counselor, and a specialist of your choice. Your team is in charge of Emily’s and her family’s care. Draft a monitoring and treatment plan and explain it.”

Then I watch them jump into discussion. You might as well imagine that you are watching a movie here. My students are the hero going into a mysterious landscape to fight a dragon, rescue everyone and save their lives. As movie audience, you gasp when the hero almost falls off a cliff and you yell when they tumble into obvious traps. “You missed the mother! The dragon got her! Save her! No, don’t go, come back, save her!” Such an obvious trap, you sigh.
Let’s be fair: my students haven’t read my blog. They have no clue how the movie would turn out. They are in it. They are in a maze of genes and mutations and pedigrees. They see Marfan the Dragon coming for Emily, and they protect her with echo and orders to stay away from sports. They brandish their weapons of Losartan and surgeries. They worry about Emily’s hypothetical children who would have 50% chance of getting Marfan. Emily’s life is a straight line that starts here, now, with her diagnosis of Marfan, and it will only go into the future with possible complications and possible sick children. It is the future of Emily that they travel to and get stuck in.
But Emily’s life does not start there. It started eight years ago when her dad’s sperm fused with her mom’s egg, creating her very first cell. When they did that, they merged their chromosomes: 23 from dad, 23 from mom. They made 23 very loving chromosome couples in Emily’s first cell. As this first cell multiplied, every cell after it would have an identical set of chromosomes made from the Original Twenty Three Pairs. These cells sculptured Emily’s hands, feet, heart, and everything else. After she came out to the world and started growing up, more cells were made, each still contained the same chromosome set made faithfully identical to the Original Twenty Three Pairs.
Chromosomes are not only loving couples who always want to be in pairs, they are also packages of genes. Because chromosomes stay in pair, the genes also stay in pairs. If chromosomes are trains, genes are very cheesy couples who always book exactly the same seats even when their trains depart from different stations. If a gene boards seat 15S on a train from mom, her partner gene will board seat 15S on the partner train from dad. When the trains meet in Emily’s cell, they can line up perfectly with each other, and so can their genes: twenty thousand pairs of genes, each has one from dad and one from mom.
It doesn’t require a whole lot of fancy science to see that all of Emily’s genes must have come from either her mom or her dad. Monolids? Definitely from dad. Thick black hair? Totally mom’s. What about Marfan? Marfan happens because Emily has a faulty gene that refuses to make normal connective tissue proteins. That gene, too, of course, must have come from either her mom or her dad.
How do we know which of her parents has that faulty gene? Well, years ago we didn’t have anyway to know that (now we do, but more on that later). Doctors would have to look at them very carefully and see who has Marfan’s symptoms. That person’s aorta would be monitored to catch any early signs of Marfan’s funny business. If someone had checked, they would have seen that Emily’s mom is tall and lanky, her arms and legs unusually long, her fingers funny looking. She had signs of Marfan. 
And it doesn’t stop there. If Emily has any siblings, they have to be checked, too, for they might have gotten the faulty gene from her mom (there is a 50% chance that they did). Emily’s mom might have gotten this gene from one of her parents — Emily’s grandparents — who might have passed it on to any of their children other than Emily’s mom. Now we have to check Emily’s uncles and aunts. And then if any of them have Marfan, they might have passed it on to their own children — Emily’s cousins. In short, all blood relatives on Emily’s mother side must be checked for Marfan. They are all at risk of being killed by a ruptured aorta until they are confirmed to be Marfan-free, or until they are diagnosed and monitored.
My students don’t see this risk. Somehow they worry about Emily’s hypothetical children yet forget about her currently living family members. They are very upset when I tell them Emily’s mother died 5 years later of aorta rupture, undiagnosed. I hope they remember it. By the time another 8-year-old girl walks into their clinic with dislocated lenses, they will remember to check her mother.
To be continued, maybe. This writing business is exhausting.

Also in “My Marfan Tale” series:

4. True love

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