In this recent (September 28th) paper in Trends in Cancer, Andrii Rozhok and James DeGregori, from the University of Colorado School of Medicine, set out to resolve what they see as two crucial limitations of past and current theories of carcinogenesis, which explain malignancy in terms of the stepwise accumulation of mutations with age. The pioneers of this idea were Peter Armitage and Richard Doll who proposed a theory for age-dependent exponential increase in cancer which was refined by Peter Nowell with his clonal expansion theory of cancer, which posits that pre-neoplastic cells, which have already accumulated some transforming mutations, expand clonally, increasing the likelihood, through time, of further oncogenic events accumulating.
Kelly Robinson and Julie Dunning Hotopp share a lab in the University of Maryland School of Medicine in Baltimore, and jointly research the role of bacterial lateral gene transfer in human disease. We’re used to human evolution putting imported viral genes to good use and there are several examples of viral genes performing vital roles in human reproduction, for instance being responsible for the formation of the layer of cells – the syncytiotrophoblast – at the junction between maternal and placental tissue. But what about the negative effects of microbial DNA – and what about bacteria?
There’s an interesting editorial on autism in PLoS Biology, written by PLoS staffer Liza Gross. She looks at several papers on the possible origins of autism that have come out since the disastrous effect on vaccination caused by the irresponsible publication of Andrew Wakefield’s throughly discredited research that implicated the measles virus in the triple vaccine, with autism.
Probably the most important paper comes from Svante Paabo and Philipp Khaitovich at the Max Planck Institute for Evolutionary Anthropology in Leipzig, together with a world-wide bunch of co-authors. Their paper is titled “Disruption of an Evolutionarily Novel Synaptic Expression Pattern in Autism”. Their study, they say, draws a connection between the genetic risk architecture of autism and molecular features of cerebral cortex development unique to humans.
Back in 1962, James Neel proposed the “thrifty-gene” hypothesis to explain rising epidemics of metabolic syndrome – obesity and its closely associated co-morbidities – throughout the western world. This suggested that, since obesity has a strong genetic component, it represented a classic case of evolutionary mismatch. Neel posited that genes for fat deposition had been selected for in times past because individuals who could efficiently store fats would be able to survive the regular occurrence of famine. In modern times that famine never comes and those thrifty genes become a liability.
Although the hypothesis has, by and large, survived for 50 years, it has not been without its critics and foremost among them is John Speakman, who used to be director of the Institute of Biological and Environmental Sciences at the University of Aberdeen, but now hails from the Institute of Genetics and Developmental Biology at the Chinese Academy of Sciences in Beijing. Speakman has taken several pot-shots at the thrifty gene hypothesis in recent years but, in this recent paper in the journal Cell Metabolism, he goes for the kill.
In direct contrast to the previous post, which preaches caution when attributing antagonistic pleiotropy to cases where palpably deleterious genes or gene variants persist despite their obvious dysgenic effects, this paper, in Proceedings Of The Royal Society B, by Grazyna Jasienska et al, uncovers a very plausible solution to why the deleterious APOE epsilon 4 gene variant persists at high frequency in modern populations despite the fact that it is linked to a 40% increased risk of cardiovascular disease and is THE major risk gene for Alzheimer’s disease, increasing the chances of carriers contracting Alzheimer’s by some fifteen times. The authors make the case that the compensating value of APOE E4 lies in increased production of the female sex hormones estrogen and progesterone which links to higher fertility. They conclude: “We show that women with the ApoE4 allele have higher levels of progesterone during the menstrual cycle, and this finding suggests, albeit indirectly, an evolutionary reason for maintaining the ancestral ApoE4 allele in the human populations, because ApoE is a major supplier of cholesterol precursor for the production of steroid hormones.”
One form of eczema, atopic dermatitis, results in very unpleasant itchy, red, scaly rashes often over large parts of the body. Blistering can occur and splitting of the skin, which can exude and leaves the skin open to infection. The genetic cause of eczema has just been used to test a central idea in evolutionary medicine to explain the continued existence at high frequency of deleterious alleles in human populations – antagonistic pleiotropy.