Psoriasis and obesity may share genetic source
Published 3 May 2016
Psoriasis is a chronic, inflammatory skin disease that affects 2-3 percent of white people globally. It has been associated with obesity, diabetes and other features of metabolic syndrome.
The Centers for Disease Control and Prevention (CDC) describe psoriasis as an autoimmune disease that involves the rapid growth of skin cells.
Symptoms of psoriasis include patches of thick, red skin with silvery scales that can itch or be painful. It can affect the knees, elbows, knees, scalp, face, lower back, palms of the hand, and soles of the feet. It can also appear around the fingernails, toenails, genitals, and inside the mouth.
Metabolic disorders and psoriasis have been linked both genetically and through environmental exposures and lifestyle choices, such as smoking, alcohol, psychological stress, levels of physical activity, and shared immunoinflammatory pathways.
Individuals with metabolic syndrome may experience a systemic inflammation that is similar to psoriasis, and, in both cases, the person may have higher levels of certain inflammatory markers, including one known as tumor necrosis factor.
Metabolic syndrome also predisposes patients to cardiovascular disease.
Psoriasis more common in twins with type 2 diabetes
Researchers can learn a lot about shared causes of diseases by using twin studies. In the current research, a team led by Dr. Ann Sophie Lønnberg, of the University of Copenhagen in Denmark, looked at data for 33,588 Danish twins aged 20-71 years. More than half the participants were women.
Participants completed a questionnaire about psoriasis, which was then matched with diagnoses for type 2 diabetes and body mass index (BMI), which was self-reported.
Psoriasis affected 4.2 percent of the participants, 630 of them men and 771 women, and 1.4 percent had diabetes. Of these, 235 were women and 224 were men.
Average BMI overall was 24.5, and 6.3 percent had a BMI of 30-34, classed as obese.
Psoriasis was present in 7.6 percent of those with diabetes, but it was only present in 4.1 percent of those without diabetes. What is more, people with psoriasis had, on average, a BMI of 25 - higher than the BMI of those without psoriasis, which stood at 24.4.
People with psoriasis had a greater risk of high BMI and obesity than those without psoriasis.
In 720 sets of twins, only one twin out of the pair had psoriasis. The twin with psoriasis also had a higher BMI and was more likely to be obese than the co-twin without psoriasis.
The authors conclude that psoriasis and obesity could partly stem from the same genetic cause, but they are careful to point out that one condition does not necessarily lead to the other.
They suggest that individuals with psoriasis may choose a more sedentary lifestyle, and that this could put them at greater risk of obesity and diabetes.
On the other hand, obesity and diabetes could be a cause of psoriasis.
Studies needed to investigate potential genetic link
Higher levels of a number of factors that have a role in the development psoriasis - such as tumor necrosis factor, tumor necrosis factor receptors, and interleukin 6 - have also been linked with obesity.
Limitations of the study include the fact that questionnaires and BMI relied on self-reporting, which may be unreliable.
Nevertheless, the authors conclude:
"Psoriasis, type 2 diabetes mellitus and obesity are strongly associated in adults after taking key confounding factors such as sex, age and smoking into account. Results indicate a common genetic etiology of psoriasis and obesity. Conducting future studies on specific genes and epigenetic factors that cause this association is relevant."
In a linked editorial, Dr. Joel M. Gelfand, of the University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, says that the findings have "clear implications" for clinical practice, especially for dermatology, where he says "a major practice gap remains" in the screening and counseling of patients for cardiovascular risk factors.
There is growing evidence, says Dr. Gelfand, of an association between psoriasis and cardiometabolic disease implying a need for change in the practice of dermatology.
Learn more about how psoriasis may increase the risk of abdominal aortic aneurysm.
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