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Authors: Armand Marie Leroi
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of them. This last statistic is intriguing, for it implies that the orientation of the viscera is randomised in right-side twins. It is as if nature, when arranging their internal organs, abandons the determinism that rules the rest of us, and instead flips a coin marked ‘left’ or ‘right’.
In recent years, much has been learned about why our internal organs are oriented the way they are. One source of information comes from those rare people – the best estimates put them at a frequency of 1 in 8500 – who, despite being born without a twin, have internal organs arranged the wrong way round. The most famous historical case of singleton situs inversus was an old soldier who died at Les Invalides in 1688. Obscure in life – just one of the thousands who, at the command of Louis XIV, had marched across Flanders, besieged Valenciennes and crossed the Rhine to chasten German princelings – he achieved fame in death when surgeons opened his chest and found his heart on the right. In the 1600s Parisians wrote doggerel about him; in the 1700s he featured in the
querelle des monstres
debate; in the 1800s he became an example of ‘developmental arrest’, the fashionable theory of the day. Were he to appear on an autopsy slab today, he would hardly be famous, but would simply be diagnosed as having a congenital disorder called ‘Kartagener’s syndrome’.
It is a diagnosis that allows us to reconstruct something of theold soldier’s medical history. Although the immediate cause of his death is not known, it certainly had nothing to do with his inverted viscera. He was, indeed, in all likelihood oblivious to his own internal peculiarities. Although he was quite healthy (dying only at the age of seventy-two), he probably never fathered any children, and his sense of smell was also probably quite poor. We can guess these things because inverted viscera, sterility and a weak sense of smell are all features of men with Kartagener’s.
That the association between these symptoms was ever noticed is surprising, for they seem so disparate, and even after the syndrome was first defined in 1936 the causal link between them remained elusive for years. But in 1976 a Swedish physiciannamed Bjorn Afzelius found that a poor sense of smell and sterility are caused by defective cilia – the minute devices that project from the surfaces of cells and wave about like tiny oars. Cilia clear particles from our bronchial passages, and the tail that drives a spermatozoon to its destination is also just a large sort of cilium. Each cilium is driven by a molecular motor, a motor that in people with Kartagener’s syndrome does not work. As children, for want of beating cilia to clear the passages of their lungs and sinuses they have chronic bronchitis and sinusitis – hence the poor sense of smell. As adults, the men are sterile for want of mobile sperm. At the heart of the ciliary motor lies a large protein complex called dyenin. It is made up of a dozen-odd smaller proteins, each of which is encoded by its own gene. So far Kartagener’s syndrome has been traced to mutations in at least two of these genes, and it is certain that others will be found.
K ARTAGENER ’ S SYNDROME . D ISSECTED INFANT SHOWING SITUS INVERSUS VISCERA . F ROM G EORGE L ECLERC B UFFON 1777
Histoire naturelle générale et particulière.
But it is the situs inversus that is so intriguing. Afzelius noted that not all people with Kartagener’s syndrome have inverted viscera: like conjoined twins, only half of them do. He suggested, insightfully, that this implied that cilia were a vital part of the devices that the embryo uses to tell left from right – but what their role was he could not say. Only in the last few years has the final link been made – and even now there is much that is obscure. It all has to do with (and this is no surprise) the organiser.
I said earlier that the organiser is a group of mesodermal cells located at one end of the embryo’s
In recent years, much has been learned about why our internal organs are oriented the way they are. One source of information comes from those rare people – the best estimates put them at a frequency of 1 in 8500 – who, despite being born without a twin, have internal organs arranged the wrong way round. The most famous historical case of singleton situs inversus was an old soldier who died at Les Invalides in 1688. Obscure in life – just one of the thousands who, at the command of Louis XIV, had marched across Flanders, besieged Valenciennes and crossed the Rhine to chasten German princelings – he achieved fame in death when surgeons opened his chest and found his heart on the right. In the 1600s Parisians wrote doggerel about him; in the 1700s he featured in the
querelle des monstres
debate; in the 1800s he became an example of ‘developmental arrest’, the fashionable theory of the day. Were he to appear on an autopsy slab today, he would hardly be famous, but would simply be diagnosed as having a congenital disorder called ‘Kartagener’s syndrome’.
It is a diagnosis that allows us to reconstruct something of theold soldier’s medical history. Although the immediate cause of his death is not known, it certainly had nothing to do with his inverted viscera. He was, indeed, in all likelihood oblivious to his own internal peculiarities. Although he was quite healthy (dying only at the age of seventy-two), he probably never fathered any children, and his sense of smell was also probably quite poor. We can guess these things because inverted viscera, sterility and a weak sense of smell are all features of men with Kartagener’s.
That the association between these symptoms was ever noticed is surprising, for they seem so disparate, and even after the syndrome was first defined in 1936 the causal link between them remained elusive for years. But in 1976 a Swedish physiciannamed Bjorn Afzelius found that a poor sense of smell and sterility are caused by defective cilia – the minute devices that project from the surfaces of cells and wave about like tiny oars. Cilia clear particles from our bronchial passages, and the tail that drives a spermatozoon to its destination is also just a large sort of cilium. Each cilium is driven by a molecular motor, a motor that in people with Kartagener’s syndrome does not work. As children, for want of beating cilia to clear the passages of their lungs and sinuses they have chronic bronchitis and sinusitis – hence the poor sense of smell. As adults, the men are sterile for want of mobile sperm. At the heart of the ciliary motor lies a large protein complex called dyenin. It is made up of a dozen-odd smaller proteins, each of which is encoded by its own gene. So far Kartagener’s syndrome has been traced to mutations in at least two of these genes, and it is certain that others will be found.
K ARTAGENER ’ S SYNDROME . D ISSECTED INFANT SHOWING SITUS INVERSUS VISCERA . F ROM G EORGE L ECLERC B UFFON 1777
Histoire naturelle générale et particulière.
But it is the situs inversus that is so intriguing. Afzelius noted that not all people with Kartagener’s syndrome have inverted viscera: like conjoined twins, only half of them do. He suggested, insightfully, that this implied that cilia were a vital part of the devices that the embryo uses to tell left from right – but what their role was he could not say. Only in the last few years has the final link been made – and even now there is much that is obscure. It all has to do with (and this is no surprise) the organiser.
I said earlier that the organiser is a group of mesodermal cells located at one end of the embryo’s
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