Murder or illness? Chemistry decides. (Chemfusion).
The doctor had seen cases like this before; the symptoms smacked of ethylene glycol poisoning. Could the boy have swallowed some antifreeze? A blood sample was sent to a laboratory and sure enough, it turned up positive for ethylene glycol, the main ingredient in commercial antifreeze.
Intravenous sodium bicarbonate was quickly administered to neutralize the excess acid and the boy soon recovered. But something seemed strange to the doctors. The mother could not account for the presence of the ethylene glycol in the baby's blood. Furthermore, there was a history of social problems in the family. Could she have tried to deliberately poison her child? Was this a case of Munchausen Syndrome by Proxy, a case in which a psychologically disturbed parent deliberately harms a child to gain attention? Social workers were called in and decided that there was sufficient evidence to place the baby with foster parents. The mother was, however, allowed visitation rights.
Eight weeks later, following a visit by his mother during which she carried out an unsupervised feeding, the young boy again began to show the same signs of illness as before. By the time the foster parents brought him to emergency, his blood had become so acidic that despite all efforts he could not be saved. Once again tests by two different laboratories confirmed the presence of ethylene glycol. This time, Patricia Stallings of St. Louis was arrested for the murder of her son.
Stallings was pregnant when arrested and gave birth in prison to a baby boy who was, of course, immediately placed with foster parents. Within a short time, the second son also began to exhibit symptoms similar to the ones which had afflicted his brother. Since the mother could not possibly have poisoned this baby, a more thorough medical evaluation was carried out. Now the diagnosis was different! Instead of ethylene glycol poisoning, the child was found to suffer from a rare genetic disease, methylmalonic acidemia (MMA).
This genetic disease occurs in roughly one in 48,000 newborns. Victims lack a properly functioning enzyme that is required to metabolize valine, isoleucine, threonine and methionine, all amino acids that commonly occur in the diet. Vitamin B12 is a required co-factor for this enzyme but for some reason in the so-called vitamin B12-responsive forms of MMA there is insufficient co-factor available to the enzyme. As a result, methylmalonic acid, a breakdown product of the abovementioned amino acids, does not get converted to the next product in the normal metabolic sequence. It is the buildup of methylmalonic acid that acidifies the blood and causes the symptoms to appear.
Interestingly, these symptoms are very similar to those seen for ethylene glycol poisoning! Ethylene glycol is metabolized to oxalic acid in the body and thereby causes acidosis in the same fashion as methylmalonic acid.
Unfortunately, the diagnosis of methylmalonic acidemia in her second child was not allowed as evidence in Stallings murder trial because the judge ruled that her defense attorney had been unable to come up with an expert witness who could testify that the genetic disease could be confused with finding ethylene glycol in the blood. The baby, like his brother, may indeed have suffered from the disease, but in the judge's view that did not preclude poisoning. In 1991, Patricia Stallings was sentenced to life imprisonment.
The story was so bizarre that it made TV's "Unsolved Mysteries." James Shoemaker and William Sly of St. Louis University, both researchers in metabolic diseases, caught the program and thought it too great a coincidence that Stallings would have poisoned her first son and then given birth to a second son who had an illness which mimicked antifreeze poisoning. They contacted the authorities and asked that they be allowed to examine blood samples from the boy who had been supposedly murdered.
A thorough analysis of these samples revealed that a staggering mistake had been made. Both the laboratories that had carried out the original analysis had erred! Using the technique of gas chromatography, which separates the components of a mixture and displays the results as a series of peaks on chart paper, they had mistaken propionic acid, a substance found in the blood of people afflicted with methylmalonic acidemia, for ethylene glycol, the antifreeze ingredient. Testing with a superior technique that combines gas chromatography with mass spectrometry (a procedure that allows exact identification of the components of a mixture) showed the presence of propionic acid.
A subsequent analysis of the baby's blood by Yale University's Piero Rinaldo confirmed the presence of methylmalonic acid. Stallings was released from prison, was reunited with her surviving child and promptly sued the hospital and the labs. The talk is that the out-of-court settlement ran into the millions. Justice had triumphed, thanks to chemistry and a little luck. Why luck? First of all, Mrs. Stallings was lucky to have been pregnant at the time of her arrest. Secondly, the odds of having a second child with methylmalonic acidemia are only one in four. And finally, an expert on genetic screening happened to be watching TV at just the right time.
Much has been learned about MMA since the Stallings affair. Recently, David Rosenblatt and Thomas Hudson, geneticists par excellence at McGill University, collaborated with Melissa Dobson and Roy Gravel of the University of Calgary to identify two genes that are linked to the vitamin B12-responsive forms of the disease. This will make early prenatal diagnosis possible and allow treatment such as vitamin B12 supplementation and a low protein diet to be initiated.
And the prosecuting attorney learned something too. That scientific evidence may not always be what it seems.
Joe Schwarcz, MCIC is the director of McGill University's Office for Science and Society You can contact him at firstname.lastname@example.org.
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|Publication:||Canadian Chemical News|
|Date:||Mar 1, 2003|
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