Thursday, July 19, 2007

Harry Potter and the Incomplete Penetrance

Via Eye on DNA: Pondering Pikaia gives an overview of controversial theories on the genetics of wizardry.

First up: the genetics of wizardry. What makes a person a wizard, and not a muggle? There was actually some discussion in the journal Nature on this very topic, back in 2005: a letter (Craig, J. Dow, R. and Aitken, M. Harry Potter and the Recessive Allele. Nature. Vol 436: 776.) and a rebuttal letter (Dodd, A., Hotta, C. and Gardner, M. Harry Potter and the Prisoner of Presumptions. Nature. Vol 437, p 318.).
The first letter claims that being being magical must depend upon a recessive allele. Wizards can have a variety of family histories: they can be born from a purely magical family, they can come from a strictly nonmagical family, or they can have one magical and one nonmagical parent (commonly scorned as "mudbloods" by haughty purebloods such as the Malfoys). Since wizards/witches can be born into muggle (nonmagical) families, Craig et al suggest that magical ability is a recessive trait (they designate the wizard allele as W and the muggle allele as M). They hypothesize that all wizards/witches are WW, which can result from a cross between two muggle "carriers" that are MW.

Tuesday, July 17, 2007

Smallpox and the Little Ice Age

Via Analog Science Fiction and Fact: Richard A. Lovett's column on "The Ice Age That Wasn't" in the April issue was partly drawn from Plows, Plagues, and Petroleum by William F. Ruddiman. An Amazon reviewer explains Ruddiman's smallpox connection:

He proposes that major plague pandemics have caused sufficient die-offs, abandonment of farms, and reforestation to temporarily lower CO2 and temperature. This could explain the later-Roman/Dark Ages lower temperatures, followed by the relatively disease-free Medieval Warming Period, in which Greenland was settled, and UK vineyards spread again to current levels, if not quite as far as early Roman. He ascribes the Little Ice Age drop to Bubonic plagues in Europe, and especially, to the death of estimated 50 million native Americans from smallpox and other European diseases.

Monday, July 16, 2007

Wolbachia and the Single Butterfly

Via John Hawks: MSNBC reports on a butterfly population that has developed resistance to the bacterial parasite Wolbachia.

Sylvain Charlat of the University of California, Berkeley, and the University College London, along with colleagues, studied the sex ratios of Hypolimnas bolina butterflies on the Samoan islands of Upolu and Savaii, where males had dwindled to 1 percent of the populations in 2001.
The likely culprit was a male-killing parasite, Wolbachia, which lives inside the butterfly’s reproductive cells, preferably female sex cells. With a female host, Wolbachia can hitch a ride to the next generation aboard the mother’s eggs. Since males are “useless” for the bacteria's survival, the parasite kills male embryos.
But the male butterflies found a way to stealthily overcome the parasites. At the beginning of 2006, the scientists found the males made up about 40 percent of Upolu’s butterfly population.
On Savaii, females still dominated the Blue Moon butterfly population (99 percent) at the start of 2006, but by the year’s end, males made up nearly 40 percent.
The team ran genetic analyses to see if the parasite had somehow vanished. It hadn’t. Wolbachia was still present in butterflies from both islands. Other lab experiments indicated the males had evolved suppressor genes to shield against the parasite.

If you find yourself a member of a suddenly or unexpectedly parthenogenic species, PlagueBlog recommends tetracycline.

Sunday, July 15, 2007

Birthwort and Balkan Nephropathy

Via ProMED-mail: New Scientist reports on the likely solution to a longstanding mystery.

Since it was first formally recognised in 1956, the disease called endemic Balkan nephropathy has perplexed experts, who have considered various explanations, including groundwater contamination.
Unlike most patients with kidney failure, people with the Balkan illness often have healthy blood pressure. Nonetheless, as their kidneys begin to fail they require dialysis and about half of them eventually develop a rare cancer of the upper urinary tract.
Arthur Grollman, at the University at Stony Brook, New York, US, did not expect to discover birthwort as the cause of this kidney disease when he set out for the region a few years ago. Instead, he had hypothesised that herbal remedies were to blame for this nephropathy.
[... H]e surveyed patients in dialysis clinics in the region on whether they had taken any herbal medicines. But none reported taking such supplements.
Disappointed his theory had proved wrong, Grollman headed for home – but not before killing a final afternoon in a library in Zagreb, the Croatian capital.
There, he came across a striking description from the 1930s about how horses in the region had developed kidney failure after grazing on a plant known as Aristolochia clematis, also known as birthwort. Grollman immediately cancelled his flight and set off to meet Balkan farmers.
A survey of their fields and mills revealed that some of their wheat was indeed contaminated with Aristolochia clematis seed. Back in the lab, Grollman and his colleagues examined kidney samples from Croatian nephropathy patients. They found the same telltale signs of DNA damage linked to Aristolochia clematis as seen in animal studies.

PlagueBlog recommends weeding the wheat.

Friday, July 13, 2007

Another Typhoid Traveller

Via ProMED-mail: The Sydney Morning Herald reports on Australia's first polio case in 21 years, imported from Pakistan by plane:

A 22-year-old man carrying the disease was in isolation in a Melbourne hospital last night and health authorities were trying to track down the 249 passengers who shared his July 2 Thai Airlines flight from Bangkok to Melbourne.
Those on flight TG999 were urged to contact the health information hotline on 1800 004 599, which is open between 8.30am and 10pm.

Thursday, July 12, 2007

Autism and Vaccines Again

Via Gene Expression: the UK Times reports on the latest autism and MMR controversy.

One of the two team members reported as resurrecting the discredited theory that MMR causes autism is Dr Carol Stott, a developmental psychologist who once worked at ARC. Baron-Cohen says she left ARC some time ago. She is now listed as a member of staff at Thoughtful House, a research centre in developmental disorders in Texas. Thoughtful House is run by Dr Andrew Wakefield, the gastroenterologist who first raised the possibility of a MMR-autism link in 1998. The other figure named as having revived the MMR-autism link was Dr Fiona Scott, who still works at ARC as an honorary research associate and runs training courses on how to diagnose autism. Scott has issued a statement denying that she privately believes in any link between MMR and autism.
Baron-Cohen says the news story is alarmist and wrong. He does not believe that MMR has anything to do with autism. “We are gobsmacked, really, at how this draft report has got out,” Baron-Cohen says. “It was only in the hands of the authors – about half a dozen people. There are three professors listed, including me, and none of us was contacted. It was also seen by two PhD students for whom I have the utmost respect because they are very careful scientists.
“I don’t believe that the MMR vaccine causes autism and I don’t believe that there are hidden environmental reasons for any rise in cases. For the moment, we should assume [any rise] is more to do with diagnostic practice.”

Wednesday, July 11, 2007

Autism, Bipolar Disorder, and Schizophrenia

Via Gene Expression, a PNAS article that correlates susceptibility to 161 diseases, pairwise, with special attention to autism, bipolar disorder, and schizophrenia. They interpret the correlations as overlap in the genetic mechanisms of (susceptibility to) the various diseases.

Our analysis suggests that, instead of following the familiar model of ‘‘unique malady–unique (disjoint with others) set of broken genes’’ applicable to most Mendelian disorders (Fig. 2D), most complex phenotypes are probably rooted in genetic variation that is significantly shared (in either a competitive or cooperative manner) by multiple disease phenotypes (Fig. 2E).
Phenotypes of non-Mendelian disorders are often defined with a considerable degree of fuzziness, especially those that are neurological: it is not uncommon to define a neuropsychiatric disease phenotype as comprising, for example, at least five of a list of 10 symptoms (4). This fuzziness arises because, in many cases, the observed disease is a heterogeneous collection of multiple maladies that have partially similar symptoms and potentially different genetic causes. However, these genetically heterogeneous maladies are combined because of the history of disease identification and the incompleteness of our knowledge about the disease causes.
Our interpretation of genetic overlap among pairs of disorders does not exclude the possibility that one disorder can cause the other. For example, it is possible that comorbidity of autism (or schizophrenia, or bipolar disorder)with infectious and autoimmune maladies indicates that the neurodevelopmental disorder can be triggered by different developmental insults, including viral or bacterial infection, or an autoimmune disease launched by a benign allergen. Another possibility is that the same molecular features that make a child more susceptible to infection or to autoimmune attack have a pleiotropic effect on brain development and function.

For the full list of overlaps, see the appendices. Appendix 1 has more pretty pictures, while 4 and 5 have some easier-to-read tables. Here's the pretty picture for plague (click to enlarge):

Monday, July 09, 2007

CDC Closes Texas A&M's Biodefense Lab

Via ProMED-mail: CIDRAP reports that the CDC has shut down Texas A&M's biodefense research lab for failure to report accidents.

In April, the Sunshine Project reported that a Texas A&M researcher had been infected with Brucella after a February 2006 aerosol chamber mishap and that the school did not immediately notify the CDC as required by federal law. Five days ago, the watchdog group reported that the exposure of three other Texas A&M workers to C burnetti, which causes Q fever, was confirmed in April 2006 but also was not reported to the CDC.

The CDC noted other concerns as well:

In the Jun 30 letter, the CDC outlined the concerns it has about the lab, which include the adequacy of biosafety plans, security of the facility from unauthorized visitors, occupational safety protocols, authorization from the CDC to work with certain agents, and compliance with federal select agent regulations.

Sunday, July 08, 2007

Nosocomial HIV Transmission in Africa

Via Gates of Vienna: Medilinks has an October 2002 article from the International Journal of STD & AIDS on HIV infections in sub-Sahara Africa not explained by sexual or vertical transmission.

An expanding body of evidence challenges the conventional hypothesis that sexual transmission is responsible for more than 90% of adult HIV infections in Africa. Differences in epidemic trajectories across Africa do not correspond to differences in sexual behavior. Studies among African couples find low rates of heterosexual transmission, as in developed countries. Many studies report HIV infections in African adults with no sexual exposure to HIV and in children with HIV-negative mothers. Unexplained high rates of HIV incidence have been observed in African women during antenatal and postpartum periods. Many studies show 20%-40% of HIV infections in African adults associated with injections (though direction of causation is unknown). These and other findings that challenge the conventional hypothesis point to the possibility that HIV transmission through unsafe medical care may be an important factor in Africa's HIV epidemic.

Although the authors of the article dance around the issue, the primary cause of the HIV epidemic in Africa appears to be the reuse of hypodermic needles. Both Marburg and Ebola have been spread nosocomially in Africa, but in that case the evidence is so immediate and bloody that no one questions it.

PlagueBlog recommends against seeking medical care in sub-Saharan Africa.