What howler monkeys can tell us about the role of interbreeding in human evolution

Did different species of early humans interbreed and produce offspring of mixed ancestry?

Recent genetic studies suggest that Neanderthals may have bred with anatomically modern humans tens of thousands of years ago in the Middle East, contributing to the modern human gene pool. But the findings are not universally accepted, and the fossil record has not helped to clarify the role of interbreeding, which is also known as hybridization.

Now a University of Michigan-led study of interbreeding between two species of modern-day howler monkeys in Mexico is shedding light on why it’s so difficult to confirm instances of hybridization among primates—including early humans—by relying on fossil remains.

The study, published online Dec. 7 in the American Journal of Physical Anthropology, is based on analyses of genetic and morphological data collected from live-captured monkeys over the past decade. Morphology is the branch of biology that deals with the form and structure of animals and plants.

The two primate species in the study, mantled howler monkeys and black howler monkeys, diverged about 3 million years ago and differ in many respects, including behavior, appearance and the number of chromosomes they possess. Each occupies a unique geographical distribution except for the state of Tabasco in southeastern Mexico, where they coexist and interbreed in what’s known as a hybrid zone.

Autism Blood Test Shows Promise

Diagnosing autism could soon be much simpler, with researchers saying this week that they’ve developed a blood test that appears to identify those with the disorder even before symptoms are apparent.

The early-stage test developed at Boston Children’s Hospital may be able to flag about two-thirds of those with autism, researchers reported in the journal PLOS ONE.

Currently, clinicians rely on observation to screen children for autism. Most kids are not diagnosed until after age 4, according to the U.S. Centers for Disease Control and Prevention.

But a blood test offers the promise of flagging kids and potentially enrolling them in early intervention programs even before symptoms appear.

In order to develop the test, researchers analyzed blood samples from 66 boys with autism and 33 without the developmental disorder in an effort to establish patterns. Ultimately, the scientists were able to focus on a group of 55 genes that they used to successfully identify autism with 68 percent accuracy in a second test group made up of 104 people with autism and 82 controls.

“It’s clear that no single mutation or even a single pathway is responsible for all cases,” said Isaac Kohane of Boston Children’s Hospital who worked on the research. “By looking at this 55-gene signature, which can capture disruptions in multiple pathways at once, we can say with about 70 percent accuracy, ‘this child does not have autism,’ or ‘this child could be at risk,’ putting him at the head of the queue for early intervention and evaluation. And we can do it relatively inexpensively and quickly.”

The blood test is not yet ready for prime time, researchers said, but it has been licensed to the company SynapDx for further exploration and potential commercialization.

Combining two genome analysis approaches supports immune system contribution to autism

Researchers using novel approaches and methodologies of identifying genes that contribute to the development of autism have found evidence that disturbances in several immune-system-related pathways contribute to development of autism spectrum disorders. The report published December 4 in the open-access journal PLOS ONE powerfully supports a role for the immune function in autism by integrating analysis of autism-associated DNA sequence variations with that of markers identified in studies of families affected by autism.

"Others have talked about immune function contributions to autism, but in our study immune involvement has been identified through a completely nonbiased approach," says Vishal Saxena, PhD, of the Massachusetts General Hospital (MGH) Department of Neurology, first, corresponding and co-senior author of the PLOS ONE paper. “We let the data tell us what was most important; and most tellingly, viral infection pathways were most important in this immune-related mechanism behind autism.”

Genetic studies of families including individuals with autism have indentified linkages with different locations in the genome. Since traditional interpretation methods implicate the gene closest to a marker site as the cause of a condition, those studies appeared to point to different genes affecting different families. However, Saxena’s team realized that, since autism has typical symptoms and affects the same biological processes, a common molecular physiology must be affecting the different families studied. To search for genetic pathways incorporating these autism-associated sites, they developed a methodology called Linkage-ordered Gene Sets (LoGS) that analyzes all of the genes within a particular distance from marker sites and ranks them according to their distance from the marker.

Genetic cause discovered for rare disorder of motor neurones

Scientists have identified an underlying genetic cause for a rare disorder of motor neurones, and believe this may help find causes of other related diseases.

Disorders of motor neurones are a group of progressive neuromuscular disorders that damage the nervous system, causing muscle weakness and wasting. These diseases affect many thousands of people in the UK. A number are inherited but the causes of the majority remain unknown, and there are no cures.

The new study has discovered a gene mutation that causes a rare disorder of motor neurones called distal hereditary motor neuropathy (dHMN). The researchers say their findings raise a possibility that mutations of the same gene or genes with similar roles might underlie other disorders of motor neurones. This could open up the potential for new treatment options, not only for dHMN but also for the wider group of these disorders.

dHMN principally affects muscles of the hands and feet, and sometimes causes a hoarse voice. Symptoms usually begin during adolescence although this can vary from infancy to the mid-thirties.

The study to investigate possible genetic causes of dHMN was led by Professor Andrew Crosby and Dr Meriel McEntagart at St George’s, University of London. It has been published in the American Journal of Human Genetics.

We all have hundreds of DNA flaws, UK geneticists say

Everyone has on average 400 flaws in their DNA, a UK study suggests. Most are “silent” mutations and do not affect health, although they can cause problems when passed to future generations. Others are linked to conditions such as cancer or heart disease, which appear in later life, say geneticists.

The evidence comes from the 1,000 Genomes project, which is mapping normal human genetic differences, from tiny changes in DNA to major mutations.

In the study, 1,000 seemingly healthy people from Europe, the Americas and East Asia had their entire genetic sequences decoded, to look at what makes people different from each other, and to help in the search for genetic links to diseases.

The new research, published in The American Journal of Human Genetics, compared the genomes of 179 participants, who were healthy at the time their DNA was sampled, with a database of human mutations developed at Cardiff University.

It revealed that a normal healthy person has on average about 400 potentially damaging DNA variations, and two DNA changes known to be associated with disease.

"Ordinary people carry disease-causing mutations without them having any obvious effect," said Dr Chris Tyler-Smith, a lead researcher on the study from the Wellcome Trust Sanger Institute, Cambridge.

He added: “In a population there will be variants that have consequences for their own health.”

The research gives an insight into the “flaws that make us all different, sometimes with different expertise and different abilities, but also different predispositions in diseases,” said Prof David Cooper of Cardiff University, the other lead researcher of the study.

Deep inside a mouse’s ear, a swirling galaxy of cells

Is this a churning galaxy in some faraway corner of the universe? A neon rose plucked by a 1990s raver? Or just a dollop of fluorescent paint swirling down the drain? Nope - it’s the cochlea of a mouse that has been stained with antibodies to reveal cells with different functions.

The image, created by Karen Avraham and Shaked Shivatzki of Tel Aviv University in Israel, was the winning entry in the GenArt 2012 human genetics image competition.

Overlaid on the twisting cochlea is a cascade of green letters that make up the DNA sequence of connexin 26. Mutations in this gene are the most common cause for deafness, says Avraham. The image is an artistic representation of deep sequencing, a technique for detecting variances in DNA.

Avraham says deep sequencing is revolutionising the hunt for genetic mutations because of its speed and low cost. Where sequencing a genome once cost millions of dollars and took years, it now takes weeks and costs about $1000.

"By finding the mutations responsible for human disease, scientists can diagnose disorders in a way that was impossible before," she says.

Human Evolution Enters an Exciting New Phase

“Most of the mutations that we found arose in the last 200 generations or so. There hasn’t been much time for random change or deterministic change through natural selection,” said geneticist Joshua Akey of the University of Washington, co-author of the Nov. 28 Nature study. “We have a repository of all this new variation for humanity to use as a substrate. In a way, we’re more evolvable now than at any time in our history.”

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Study Confirms AKT1 Genotype Contributes to Risk of Cannabis Psychosis

The ability of cannabis to produce psychosis is an important public health concern. Some studies have suggested that cannabis exposure during adolescence may increase the risk of developing schizophrenia.

For these reasons, it would be valuable if a biological test could be developed that predicted the risk of developing psychosis in people who abuse cannabis or use marijuana as a medication.

A recent study has implicated a variation in the gene that codes for a protein called RAC-alpha serine/threonine-protein kinase in the risk for cannabis psychosis. However, independent verification of these finding is critical for genetic associations with complex genetic traits, like cannabis-related psychosis, because these findings are difficult to replicate.

Dr Forti’s team carried out a case control study to investigate variation in the AKT1 gene and cannabis use in increasing the risk of psychosis.

“We studied the AKT1 gene as this is involved in dopamine signaling which is known to be abnormal in psychosis. Our sample comprised 489 patients with their first episode of psychosis and 278 healthy controls,” explained Dr Forti, who, with colleagues, reports on the results in the journal Biological Psychiatry.