The largest DNA-sequencing study of anorexia nervosa has linked the eating disorder to variants in a gene coding for an enzyme that regulates cholesterol metabolism. The finding suggests that anorexia could be caused in part by a disruption in the normal processing of cholesterol, which may disrupt mood and eating behaviour.

‘These findings point in a direction that probably no one would have considered taking before,’ said Nicholas J. Schork, a professor at The Scripps Research Institute (TSRI). Schork was the senior investigator for the multicenter study.

Anorexia affects up to 1 percent of women, and has an estimated mortality rate of 10 or more percent, making it perhaps the deadliest of psychiatric illnesses. Anorexics severely restrict eating and become emaciated, yet see themselves as fat. Individuals with anorexia nervosa tend to be perfectionistic, anxious or depressed, and obsessive, said Walter Kaye, a co-author on the study, professor at the University of California (UC), San Diego School of Medicine and principal investigator of the Price Foundation Genetic Studies of Anorexia Nervosa.

How the disorder develops is still not fully understood. Anorexia predominantly affects girls and young women (the estimated gender ratio is nearly 10:1) and appears to be influenced in part by cultural factors, stress, puberty and social networks. Yet twin studies suggest that genetic factors have the largest influence.

The big mystery has been: what are those genetic factors? Gene-association studies of anorexics have so far produced few replicable findings. Researchers suspect that many genes can contribute to the disorder—and thus only large studies will have the statistical power to detect those individual genetic influences.

For this project—the largest-ever sequencing study of anorexia—Schork worked with an international team of collaborators representing more than two dozen research institutions. The many contributors included first author Ashley Scott-Van Zeeland from The Scripps Translational Science Institute and Scripps Health in La Jolla, California; Kaye and Pei-an Betty Shih from the UC San Diego; Andrew Bergen from SRI International in Menlo Park, California; Wade Berretini from the University of Pennsylvania; and Pierre Magistreti from Ecole Polytechnique Fédérale de Lausanne. The project made use of genetic information from more than 1,200 anorexia patients and nearly 2,000 non-anorexic control subjects.

For an initial ‘discovery’ study in 334 subjects, the researchers catalogued the variants of a large set of genes that had already been linked to feeding behavior or had been flagged in previous anorexia studies. Of more than 150 candidate genes, only a handful showed statistical signs of a linkage with anorexia in this group of subjects.

One of the strongest signs came from the gene EPHX2, which codes for epoxide hydrolase 2—an enzyme known to regulate cholesterol metabolism. ‘When we saw that, we thought that we might be onto something, because nobody else had reported this gene as having a pronounced role in anorexia,’ said Schork.

The team followed up with several replication studies, each using a different cohort of anorexia patients and controls, as well as different genetic analysis methods. The scientists continued to find evidence that certain variants of EPHX2 occur more frequently in people with anorexia.

To help make sense of these findings, they looked at existing data from a large-scale, long-term heart disease study and determined that a subset of the implicated EPHX2 variants have the effect of altering the normal relationship between weight gain and cholesterol levels.

‘We thought that with further studies this EPHX2 finding might go away, or appear less compelling, but we just kept finding evidence to suggest that it plays a role in anorexia,’ said Schork.

It isn’t yet clear how EPHX2 variants that cause an abnormal metabolism of cholesterol would help trigger or maintain anorexia. But Schork noted that people with anorexia often have remarkably high cholesterol levels in their blood, despite being severely malnourished. Moreover, there have been suggestions from other studies that weight loss, for example in people with depression, can lead to increases in cholesterol levels. At the same time, there is evidence that cholesterol, a basic building block of cells, particularly in the brain, has a positive association with mood. Conceivably, some anorexics for genetic reasons may feel an improved mood, via higher cholesterol, by not eating.

‘The hypothesis would be that in some anorexics the normal metabolism of cholesterol is disrupted, which could influence their mood as well as their ability to survive despite severe caloric restriction,’ said Schork.

For now that’s just a hypothesis, which Schork emphasized should be investigated further with more gene association studies and more studies of EPHX2 variants’ biological effects.

The study was funded principally by the Price Foundation of Switzerland. ‘It was a long and difficult study and the foundation was very gracious and patient, and that was important,’ Schork said. The Scripps Research Institute

Protein being studied to fight cancer; may cause toxicity in cardiac cells
A study by researchers at Skaggs School of Pharmacy and Pharmaceutical Sciences and the Department of Pharmacology at the University of California, San Diego, shows that a protein called MCL-1, which promotes cell survival, is essential for normal heart function.

Their study found that deletion of the gene encoding MCL-1 in adult mouse hearts led to rapid heart failure within two weeks, and death within a month.

MCL-1 (myeloid cell leukemia-1) is an anti-apoptotic protein, meaning that it prevents or delays the death of a cell. It is also a member of the BCL-2 family of proteins that regulate mitochondria – the cell’s power producers – and cell death. Aberrant expression of anti-apoptotic BCL-2 family members is one of the defining features of cancer cells, and is strongly associated with resistance to current therapies. Thus, these proteins are currently major targets in the development of new therapies for patients with cancer.

But, while MCL-1 is up regulated in a number of human cancers, contributing to the overgrowth of cancer cells, it is found at high levels in normal heart tissue. Additionally, the researchers found that autophagy – a process which deals with mitochondrial maintenance and is normally induced by myocardial stress – was impaired in mice with MCL-1 deficient hearts.
In summary, the study demonstrated that the loss of MCL-1 led to rapid dysfunction of mitochondria, impaired autophagy and heart failure, even in the absence of cardiac stress.

‘Cardiac injury, such as a heart attack, causes levels of MCL-1 to drop in the heart, and this process may increase cardiac cell death,’ said Åsa B. Gustafsson, PhD, an associate professor at UCSD Skaggs School of Pharmacy and Pharmaceutical Sciences. ‘Therefore, preserving normal levels of this protein in cardiac tissue could reduce damage after a heart attack and prevent progression to heart failure.’

By compromising both autophagy and mitochondrial function, MCL-1 inhibitors are likely to affect the cells’ energy supply. ‘Our findings raise concerns about the potential cardiac toxicity of drugs that block MCL-1 – drugs that have entered clinical trials because they increase cancer cell death,’ said the study’s first author, Robert L. Thomas. Skaggs School of Pharmacy and Pharmaceutical Sciences

Obesity gene testing does not put people off weight loss and may help to reduce self-blame, according to a new study by researchers from the Health Behaviour Research Centre at UCL.

Previous studies have shown that genes play a role in a person’s risk of becoming overweight. One gene, called FTO, has been found to have the biggest influence so far.

FTO has two variants, one associated with greater risk of weight gain (A) and one associated with lower risk (T). One in two people carries at least one copy of the A variant. People who inherit two A variants (one from their mother and one from their father) are 70% more likely to become obese than those with two T variants. Even those who inherit one have a higher weight than those with two T variants.

Researchers can now use a gene test for FTO (although this is not yet commercially available). However, it was not known how people would react to finding out the results of the genetic test.
Regardless of gene status or weight, all the volunteers recognised that both genes and behaviour are important for weight control. The results indicate that people are unlikely to believe that genes are destiny and stop engaging with weight control once they know their FTO status.
Some clinicians thought it would help people to become motivated to manage their weight. Others thought that the ‘genes as destiny’ perspective might mean people felt there was nothing they could do about their weight. If people responded fatalistically it could be harmful because diet and exercise are still very important for health and weight control, perhaps even more so if a person is ‘battling against their biology’.

UCL’s Professor Jane Wardle and Susanne Meisel decided to test a small number of volunteers (18) for their FTO status and interview them about their experience. The sample of volunteers included men and women, who spanned the weight range from underweight to obese.

They found that the volunteers were very enthusiastic about receiving their genetic test result. Those who struggled with their weight said that the genetic test result was helpful because it removed some of the emotional stress attached to weight control and relieved some of the stigma and self-blame.

No one reported a negative reaction to the genetic test result, or said it made them feel there was nothing they could do to about their weight.

Susanne Meisel, who led the study said: ‘These results are encouraging. Regardless of gene status or weight, all the volunteers recognised that both genes and behaviour are important for weight control. The results indicate that people are unlikely to believe that genes are destiny and stop engaging with weight control once they know their FTO status. Although they knew that FTO’s effect is only small, they found it motivating and informative. We are now doing a larger study to confirm whether more people react in the same way.’ University of College London

Massachusetts General Hospital (MGH) researchers have identified and validated two rare gene mutations that appear to cause the common form of Alzheimer’s disease (AD) that strikes after the age of 60. The two mutations occur in a gene called ADAM10 – coding for an enzyme involved in processing the amyloid precursor protein – which now becomes the second pathologically-confirmed gene for late-onset AD and the fifth AD gene overall.
In their report the investigators from the MassGeneral Institute for Neurodegenerative Disease (MGH-MIND) describe how the two mutations in ADAM10 increase generation and accumulation of the toxic amyloid beta (A-beta) protein in the brains of a mouse model of AD. The mutations also reduce generation of new neural cells in hippocampus, a part of the brain essential to learning and memory.
‘This is the first report to document, in animal models, new pathogenic gene mutations for AD since the reports of the original four genes in the 1990s,’ says Rudolph Tanzi, PhD, director of the Genetics and Aging Research Unit at MGH-MIND and senior author of the Neuron paper. ‘What we found regarding the many effects of these two rare mutations in ADAM10 strongly suggests that diminished activity of this enzyme can cause AD, and these findings support ADAM10 as a promising therapeutic target for both treatment and prevention.’
The process leading to the generation of A-beta – which accumulates in characteristic plaques in the brains of AD patients – begins when the amyloid precursor protein (APP) is cut into smaller proteins by enzymes called secretases. A-beta results if APP is first cut into two segments by an enzyme called beta-secretase, and one of those segments is further cut by a gamma-secretase enzyme to release the toxic A-beta fragment. However, processing of APP by an alpha-secretase enzyme – one of which is ADAM10 – cuts right through the A-beta region in APP. So instead of generating the toxic A-beta fragment, cleavage with alpha-secretase produces a protein fragment that has been reported to protect and stimulate the generation of neurons in brain.
An earlier study by Tanzi’s team reported finding that either of two mutations in ADAM10 increased the risk of AD in seven families with the late-onset form of the disease. Since ADAM10 was already known to be important to alpha-secretase processing of APP, along with having a role in early brain development, the researchers set out to investigate how the observed mutations might lead to the pattern of neurodegeneration characteristic of AD.
Experiments using several strains of transgenic mice – including lines that express both one of the ADAM10 mutations and an APP mutation that leads to AD-like pathology – revealed the following:
AD-associated mutations in ADAM10 reduced the release from neurons in the animals’ brains of the beneficial protein produced by alpha-secretase processing of APP,
Reduced ADAM10 activity caused by the mutations increased the generation of A-beta and its accumulation in plaques, along with producing other AD-associated neurodegenerative signs,
Reduced ADAM10 activity also impaired the generation of new neurons in the hippocampus, one of the areas of the brain most vulnerable to neurodegeneration in AD,
The AD-associated mutations produce these effects by impairing the correct folding of ADAM10 and interfering with its normal functions.
Jaehong Suh, PhD, of the MGH-MIND Genetics and Aging Research Unit, lead author of the Neuron article, says, ‘Our current study shows that reducing ADAM10 activity by these AD-associated mutations delivers a ‘one-two punch’ to the brain – one, decreasing neuroprotective alpha-secretase cleavage products and two, increasing neurotoxic A-beta protein accumulation. Thus, we believe that increasing ADAM10 activity might help to alleviate both genetic and environmental AD risk factors that increase the toxic beta-secretase processing of APP. We’re planning to develop optimal ways to increase ADAM10 activity in brain and to further investigate the molecular structure and regulatory mechanism of the ADAM10 enzyme.’ Suh is an instructor in Neurology, and Tanzi is the Joseph P. and Rose F. Kennedy Professor of Neurology at Harvard Medical School. Massachusetts General Hospital