Everyday entropy: trisomy


My son was born with mosaic trisomy 18. For people who know these things, it is better known as Edward’s syndrome, which is a chromosomal condition in which cells contain three copies of the 18th chromosome. Down’s syndrome occurs when cells contain three copies of the 21st chromosome. Trisomy is generally considered a genetic disorder, but disorder is the wrong word. There’s nothing wrong with the order of the genes, it’s just that there is an extra copy of one of the chromosomes. The extra copy of the chromosome is not in any way malignant. It isn’t like there are two good copies and one bad copy. All three copies are in perfect working order and fine in their own right, so if any one of the three were to disappear, the cell would behave normally. This is just information, and people with trisomy just have too much of it.

Understanding how too much information can be catastrophic is not entirely intuitive. What you have to remember is that most of the processes in the human body are balanced against other processes, and in constant tension between two extremes. One obvious example is the biceps and triceps. If you took away someone’s triceps, their arm wouldn’t work half as well, it wouldn’t work at all. In trisomies like Edward’s and Down’s syndromes, the damage comes from the over-expression of some trait that is finely balanced against another trait, like the balance between nerve cell fibre and nerve cell insulation. Too much insulation may choke off the cell completely, or lead to Alzheimer’s disease in adults with Down’s.

One of the first questions we were asked when my son was born was whether he looked like his brother. None of the doctors or nurses knew why he had such low tone, low oxygen and difficulty swallowing, but the experienced staff had this intuition, and genetic conditions often cause facial anomalies. But it was hard to tell. He was born with severe swelling on one side of his face and when the swelling subsided there was a palsy that immobilised that side, and he had a feeding tube in his nose. We waited ten days for the genetic tests to come back.

When the doctor told us that he had Edwards syndrome, I cried. I don’t cry often, maybe at the end of Apollo 13 when they make in through reentry, but not for normal human things. The doctor was surprised, not because he knew I don’t cry, but because he didn’t expect me to know what Edwards syndrome was. I knew because his 18 week ultrasound had shown that his fists were clenched and his foot turned inwards. The obstetrician mentioned Edwards in passing, but she told us not to worry because he didn’t have holes in his heart or misplaced kidneys and his brain and major organs looked okay. Edwards syndrome is catastrophic. From that moment, he was like schroedinger’s baby, indetminately living and dying at the same time, based totally on the inaccessible information in his cells.

Edwards syndrome is generally incompatible with life, but the mosaic form is special. In my son’s case, only some of his cells have a third copy of chromosome 18, maybe 15%. When he was small, his life hung in the balance of whether too many trisomy cells would be called on to perform too many critical functions. He was like a Rorschach test for the doctors. The optimists focussed on his functioning heart, his stable breathing, his hair, his skin; the pessimists asked us whether we wanted him to be resuscitated if he went into arrest; and the technicians focussed on the details of the feeding tube keeping him comfortable.

He was drowning in information. There was nothing in him that was diseased. His genetic code was fine. The only problem was that the machinery of biology has no sense of irony. It can’t disregard a message, once received. When a virus enters a cell, the cell’s processors can’t do anything but translate and transcribe it’s message, even though the message spells the cell’s demise.  We tend to think of viruses as biological aberrations without value for life, but we have to remember that 40% of bacteria are killed by viruses every day, so without viruses the bacteria in the ocean would multiply astronomically. Viruses may not be alive, but they are a meaningful part of life’s network of information. They are messages that have escaped the dead letter office and can’t but be repeated. His extra chromosome was not malevolent, misshapen or misguided, but his cells had no way of knowing that they were not meant to follow the extra instructions the same as the initial instructions.

It is as though he were hit with a bullet, but instead of obliterating everything in its path, it spread itself over his whole body and randomly eliminated a set of cells he could live without. He isn’t unaffected, and there is no way to know how he will be affected in the future, but he is all there. It is hard to say that he is lucky, but it is equally hard to say that he is unlucky.


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