Natural selection can actually favor an otherwise harmful allele of a gene, if that allele somehow confers a survival advantage in some individuals and populations. The one textbook example of this phenomenon has always been sickle cell disease, a genetically inherited disease that results in deformed red blood cells and can lead to early death. Sickle cell disease is prevalent in persons of African ancestry because the allele that causes sickle cell disease also protects the person with that allele from malaria, a disease which is widespread in Africa.
Now there’s a second example of this phenomenon. Researchers have found that two different alleles for a gene involved in the production of a blood protein can; a) lead to kidney disease, and b) protect against the parasite that causes African sleeping sickness. Not surprisingly, the two abnormal alleles and the kidney diseases they cause are four to five times more common in African Americans than in persons of European descent.
Researchers are wondering how many other genetic diseases we’ll find that also confer protective advantages against certain infectious diseases. Researchers are also hoping to develop new treatments for African sleeping sickness that are based on the proteins these abnormal alleles produce.
Tampilkan postingan dengan label Urinary system. Tampilkan semua postingan
Tampilkan postingan dengan label Urinary system. Tampilkan semua postingan
Minggu, 22 Agustus 2010
Kamis, 06 Mei 2010
How Safe is Live Kidney Donation?
It’s been about 60 years since the first live kidney donor operation. There have been scattered reports that kidney donation is safe, but most published studies have been limited in scope and used inappropriate control groups against which to compare mortality statistics.
A recent report strengthens the hypothesis that live kidney donation is relatively safe. The report compares mortality data for essentially all 80,347 live kidney donors in the United States between 1994 and 2009 to a carefully matched control group of people who were eligible to donate but were not asked to do so. Mortality statistics were followed in both groups for up to 12 years (median 6.3 years) after donation by the live kidney donor group.
The results indicate that there is a small risk of death from the surgical procedure itself, as would be expected of any similar major surgical procedure. Early post-surgical (three-month) mortality was 3.1 per 10,000 kidney donors, compared to 0.4 deaths in the control group over a similar three-month period. After that, however, there were no differences in survival between the donor and control groups out to 12 years.
The results support the hypothesis that there is no long-term mortality risk associated with live kidney donation except for the usual risks of surgery. Presumably a follow-up study will be done in years ahead to extend the definition of “long-term” to beyond 12 years.
A recent report strengthens the hypothesis that live kidney donation is relatively safe. The report compares mortality data for essentially all 80,347 live kidney donors in the United States between 1994 and 2009 to a carefully matched control group of people who were eligible to donate but were not asked to do so. Mortality statistics were followed in both groups for up to 12 years (median 6.3 years) after donation by the live kidney donor group.
The results indicate that there is a small risk of death from the surgical procedure itself, as would be expected of any similar major surgical procedure. Early post-surgical (three-month) mortality was 3.1 per 10,000 kidney donors, compared to 0.4 deaths in the control group over a similar three-month period. After that, however, there were no differences in survival between the donor and control groups out to 12 years.
The results support the hypothesis that there is no long-term mortality risk associated with live kidney donation except for the usual risks of surgery. Presumably a follow-up study will be done in years ahead to extend the definition of “long-term” to beyond 12 years.
Senin, 26 April 2010
Paying Living Donors for a Kidney
Arguments against paying living donors for a kidney generally focus on two ethical concerns; 1) that payments might induce a potential donor to ignore the risks associated with kidney donation, and 2) that payments might exploit poor people, who would have a greater incentive to donate than wealthier persons.
To test these concerns, a team of researchers polled 342 potential donors in Philadelphia. The study found that potential donors’ perception of the risk of kidney donation is completely unaltered by how much money is offered for their kidney ($0, $10,000, or $100,000). The study also found that although a potential donor’s willingness to donate is influenced by money (more money, more willingness to donate), the effect of money was the same across all income strata. In other words, there was no evidence that payments would either induce donors to ignore risk or specifically exploit poor people.
Based on these data, perhaps payments should be offered to donors on a trial basis. It’s worth knowing whether potential donors’ actual choices would be the same as their hypothetical choices on a survey.
To test these concerns, a team of researchers polled 342 potential donors in Philadelphia. The study found that potential donors’ perception of the risk of kidney donation is completely unaltered by how much money is offered for their kidney ($0, $10,000, or $100,000). The study also found that although a potential donor’s willingness to donate is influenced by money (more money, more willingness to donate), the effect of money was the same across all income strata. In other words, there was no evidence that payments would either induce donors to ignore risk or specifically exploit poor people.
Based on these data, perhaps payments should be offered to donors on a trial basis. It’s worth knowing whether potential donors’ actual choices would be the same as their hypothetical choices on a survey.
Sabtu, 03 Oktober 2009
Encouraging Organ Donations
Fewer than 40% of all adults have signed a donor card or other legal document indicating their willingness to donate their organs after death. Perhaps it’s a form of avoidance, but for whatever reason we just don’t seem to get around to it. "Presumed consent" laws are one solution, but some people find presumed consent laws objectionable on the grounds that they are a form of religious discrimination. Under presumed consent, it's people who do not wish to donate (perhaps for religious reasons) who must make their wishes known in advance, not the other way around.
One innovative and eminently fair solution is to require everyone to make their wishes known. Its called “mandated choice”. In the State of Illinois, every person over the age of 18 who renews a driver’s license must answer the question, “Do you wish to be an organ donor?” The state now has a donor signup rate of 60%. Several other states (Pennsylvania, for one) ask the question as well, but it's for informational purposes only. In Illinois, the answer is considered legally binding, meaning that relatives cannot later overturn it.
Senin, 03 Agustus 2009
Buying/Selling Kidneys
A Brooklyn businessman named Levy-Izhak Rosenbaum was arrested in New Jersey in 2009 for allegedly trying to broker the purchase of a kidney for $160,000. According to the criminal complaint filed against him, Mr. Rosenbaum told an undercover agent that he could arrange for a live kidney donor from Israel, and that they would then fabricate a fictitious “relationship” between the donor and the recipient so that the hospital in the U.S. would not become suspicious.
The Rosenbaum case is just one example of the shadowy black market in human organs worldwide. The World Health Organization estimates that about 10% of the more than 60,000 kidneys transplanted each year come from living donors who have sold their kidneys strictly for money. The temptation is hard to resist, especially for donors from poor countries where the choice may come down to selling a kidney or selling a child. The practice is not even illegal in some countries (Pakistan is an example), and as a result those countries are rapidly developing thriving “transplant tourism” enterprises.
What, if anything, could be done about the shortage of organs for transplantation?
The Rosenbaum case is just one example of the shadowy black market in human organs worldwide. The World Health Organization estimates that about 10% of the more than 60,000 kidneys transplanted each year come from living donors who have sold their kidneys strictly for money. The temptation is hard to resist, especially for donors from poor countries where the choice may come down to selling a kidney or selling a child. The practice is not even illegal in some countries (Pakistan is an example), and as a result those countries are rapidly developing thriving “transplant tourism” enterprises.
What, if anything, could be done about the shortage of organs for transplantation?
Selasa, 23 Juni 2009
Steve Jobs' New Liver
It’s not official, but there are reports in the news media that Steve Jobs, CEO of Apple computers, received a liver transplant recently at an undisclosed location in Tennessee (The New York Times, June 23; “A Transplant That is Raising Many Questions”).
Normally, patients who need an organ transplant place themselves on the transplant list of one of eleven regional Organ Procurement Organizations (OPOs) in the U.S. Waiting times can vary. When an organ becomes available the regional OPO offers it to a patient already on its list, with the highest priority given to the sickest patients and those who have been on the list the longest time.
Most patients sign up for the transplant list at only one OPO, because insurance companies will only pay for an organ transplant performed in a person’s “home” OPO. Nevertheless, patients who are willing to pay for the transplant themselves (and with access to a plane so they can get to the hospital within six hours) can increase their odds for a transplant by placing themselves on the transplant lists of several different OPOs simultaneously. No one has said whether or not Mr. Jobs was on more than one list at the time of his transplant, or how long he waited for his new liver.
For a discussion of whether the current organ allocation system is fair, see “How Should We Allocate Scarce Organs?” in Human Biology 5th ed., pp. 368-369.
Normally, patients who need an organ transplant place themselves on the transplant list of one of eleven regional Organ Procurement Organizations (OPOs) in the U.S. Waiting times can vary. When an organ becomes available the regional OPO offers it to a patient already on its list, with the highest priority given to the sickest patients and those who have been on the list the longest time.
Most patients sign up for the transplant list at only one OPO, because insurance companies will only pay for an organ transplant performed in a person’s “home” OPO. Nevertheless, patients who are willing to pay for the transplant themselves (and with access to a plane so they can get to the hospital within six hours) can increase their odds for a transplant by placing themselves on the transplant lists of several different OPOs simultaneously. No one has said whether or not Mr. Jobs was on more than one list at the time of his transplant, or how long he waited for his new liver.
For a discussion of whether the current organ allocation system is fair, see “How Should We Allocate Scarce Organs?” in Human Biology 5th ed., pp. 368-369.
Kamis, 26 Maret 2009
The PSA Test for Prostate Cancer
For over 20 years some health professionals have been recommending that men over 50, and men as young as 45 if they belong to a high-risk group, be screened for prostate cancer by means of a PSA test (see Human Biology 5th ed., table 18.4). The PSA test measures the level of prostate-specific antigen, a protein from prostate cells. An elevated serum PSA indicates that prostate cancer might be present, in which case the next step is a biopsy to determine for sure.
When the PSA test was first introduced in 1987, scientists thought it might lead to as much as a 50% reduction in prostate cancer deaths. But now it seems that it may not save lives after all. In a study of 77,000 U.S. men, the 10-year death rate from prostate cancer was the same in a group who had an annual PSA test for six years plus a digital rectal examination for four years, compared to a control group who were never tested over the same time period. The study may need to be continued out for another decade or so to determine whether the PSA test has any usefulness over the longer term, however.
How can a test that accurately detects prostate tumors not save lives? Apparently the answer is that most prostate cancers are so slow-growing that older men are likely to die of something else first, even if they do have a diagnosis of prostate cancer. For older men, skipping the PSA test altogether may someday be safe option.
By the way, a digital rectal examination is not some sort of digital readout. It's a physician’s gloved digit, or finger.
When the PSA test was first introduced in 1987, scientists thought it might lead to as much as a 50% reduction in prostate cancer deaths. But now it seems that it may not save lives after all. In a study of 77,000 U.S. men, the 10-year death rate from prostate cancer was the same in a group who had an annual PSA test for six years plus a digital rectal examination for four years, compared to a control group who were never tested over the same time period. The study may need to be continued out for another decade or so to determine whether the PSA test has any usefulness over the longer term, however.
How can a test that accurately detects prostate tumors not save lives? Apparently the answer is that most prostate cancers are so slow-growing that older men are likely to die of something else first, even if they do have a diagnosis of prostate cancer. For older men, skipping the PSA test altogether may someday be safe option.
By the way, a digital rectal examination is not some sort of digital readout. It's a physician’s gloved digit, or finger.
Kamis, 12 Februari 2009
Using Urine to Diagnose Disease
Your body gets rid of over a thousand different small metabolic waste molecules, called metabolites, by excreting them in the urine. In certain diseases one or more of these metabolites may be elevated in urine. Scientists now believe that through “metabolomics” – the study of metabolites – it may be possible to diagnose certain diseases even before symptoms appear in the patient.
The concept is simple; once you know the normal range of excretion of metabolites in urine, a change in the excretion of one or more metabolites might signal the presence of a specific disease. For example, scientists at the University of Michigan measured 1,126 metabolites in urine and found that one of them in particular, called sarcosine, showed promise as a marker for metastatic prostate cancer. The findings were reported in Nature this month.
Unlike blood, urine is easily collected in large quantities by non-invasive techniques. (Put more bluntly, you just pee into a cup!) As the field of metabolomics comes of age, perhaps some day it will be possible to screen for dozens of diseases at once.
The concept is simple; once you know the normal range of excretion of metabolites in urine, a change in the excretion of one or more metabolites might signal the presence of a specific disease. For example, scientists at the University of Michigan measured 1,126 metabolites in urine and found that one of them in particular, called sarcosine, showed promise as a marker for metastatic prostate cancer. The findings were reported in Nature this month.
Unlike blood, urine is easily collected in large quantities by non-invasive techniques. (Put more bluntly, you just pee into a cup!) As the field of metabolomics comes of age, perhaps some day it will be possible to screen for dozens of diseases at once.
Jumat, 23 Januari 2009
Gender Bias in Kidney Transplants
According to a recent online report that will be published shortly in the Journal of the American Society of Nephrology, women over the age of 45 who need a kidney transplant are less likely to get one than men of the same age. This despite the fact that they are no sicker than the men and would benefit just as much as the men by having a kidney transplant.
So why the bias against older women? The researchers aren’t sure, but they speculate that women may be seen as more frail than they actually are by whoever makes the decision to put (or not to put) a female patient on the deceased-donor waiting list or to help them find a live donor. Or, perhaps the women themselves think they are less likely to survive the surgery or benefit from the transplant. But if its not true, women and their families will need to know that.
The issue of how we allocate scarce organs like kidneys is discussed in Human Biology 5th ed., pp. 368-369.
Future REFERENCE: Segev, Dorry et al: "Age and Comorbidities are Effect Modifiers of Gender Disparities in Renal Transplantation". J. Am. Soc. Nephrol. 000:00-00, 2009.
So why the bias against older women? The researchers aren’t sure, but they speculate that women may be seen as more frail than they actually are by whoever makes the decision to put (or not to put) a female patient on the deceased-donor waiting list or to help them find a live donor. Or, perhaps the women themselves think they are less likely to survive the surgery or benefit from the transplant. But if its not true, women and their families will need to know that.
The issue of how we allocate scarce organs like kidneys is discussed in Human Biology 5th ed., pp. 368-369.
Future REFERENCE: Segev, Dorry et al: "Age and Comorbidities are Effect Modifiers of Gender Disparities in Renal Transplantation". J. Am. Soc. Nephrol. 000:00-00, 2009.
Rabu, 17 Desember 2008
Incentives for Organ Donations
There are now over 100,000 patients waiting for an organ transplant. Over 6,000 of them will die this year because they will not find a suitable organ in time. The problem, as discussed in Human Biology 5th ed. (pp. 368-369), is simply too few available organs for too many patients. Aside from the fact that finding a good match among unrelated donors is relatively rare, healthy people are often reluctant to donate an organ for emotional reasons and there is no financial incentive for organ donations. In fact, current federal law states that a person can go to jail and be fined $50,000 if “valuable consideration” is given to a donor. The law was meant to discourage commercial trafficking in human organs (considered to be exploitive of the poor), but it has also had a chilling effect on altruistic giving.
But that may soon change. Senator Arlen Specter of Pennsylvania will introduce a bill next year that would allow states to offer certain “incentives” to donors and their families, such as tax credits, contributions to 401K retirement plans, and tuition vouchers. The bill still would still prohibit the direct buying and selling of organs, however, so you won’t be able to buy a kidney on eBay any time soon.
One patient’s emotional odyssey as her kidneys began to fail is described in “Desperately Seeking a Kidney” published two days ago in the New York Times. It might make an interesting additional reading assignment for your students.
But that may soon change. Senator Arlen Specter of Pennsylvania will introduce a bill next year that would allow states to offer certain “incentives” to donors and their families, such as tax credits, contributions to 401K retirement plans, and tuition vouchers. The bill still would still prohibit the direct buying and selling of organs, however, so you won’t be able to buy a kidney on eBay any time soon.
One patient’s emotional odyssey as her kidneys began to fail is described in “Desperately Seeking a Kidney” published two days ago in the New York Times. It might make an interesting additional reading assignment for your students.
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