People with high socioeconomic status jobs are believed to be better off in life.
New research published last week by the Centre for Disease Control, however, suggests that this may not be the case with regards to one’s risk of developing Parkinson’s disease.
In today’s post we will review the research and discuss what it means for our understanding of Parkinson’s disease.
The impact of socioeconomic status. Source: Medicalxpress
In 2013, a group of researchers at Carnegie Mellon University found a rather astonishing but very interesting association:
Children from lower socioeconomic status have shorter telomeres as adults.
Yeah, wow, strange… sorry, but what are telomeres?
Do you remember how all of your DNA is wound up tightly into 23 pairs of chromosomes? Well, telomeres are at the very ends of each of those chromosomes. They are literally the cap on each end. The name is derived from the Greek words ‘telos‘ meaning “end”, and ‘merοs‘ meaning “part”.
Telomeres are regions of repetitive nucleotide sequences (think the As, Gs, Ts, & Cs that make up your DNA) at each end of a chromosome. Their purpose seems to involve protecting the end of each chromosome from deteriorating or fusing with neighbouring chromosomes. Researchers also use their length is a marker of ageing because every time a cell divides, the telomeres on each chromosome gradually get shorter.
There is a question that pops up regularly when I speak at local Parkinson’s UK support group:
‘Do you think there is a certain type of personality that is more vulnerable to Parkinson’s disease?’
And my answer:
‘This is a question that pops up regularly. It is very controversial, but there is some evidence to suggest that ‘yes’ there are certain personality traits’
Here is what we know:
In 1913, Dr Carl Camp, a neurologist at the University of Michigan, wrote in ‘Modern Treatment of Nervous and Mental Diseases’:
“It would seem that paralysis agitans affected mostly those persons whose lives had been devoted to hard work… The people who take their work to bed with them and who never come under the inhibiting influences of tobacco or alcohol are the kind that are most frequently affected. In this respect, the disease may be almost regarded as a badge of respectable endeavor”
Cited from Menza M. (2000).
Dr Carl Camp. Source: OldNews
It was the first observation that there may be personality traits are shared between people who go on to develop Parkinson’s disease. Since Dr Camp’s comment, over 100 years ago now, there are almost 100 studies that have looked at this topic and the majority of them have agreed that certain personality traits that are associated with increased risk of Parkinson’s disease.
These traits include:
- Lack of novelty seeking
And the evidence suggests that these traits persist long after the onset of the illness – that is to say, they are not affected by the disease.
Now it should be NOTED that this area of research remains controversial, and simply having some of these personality traits does not immediately mean that you will go on to develop Parkinson’s disease.
The most interesting results have come from studies comparing twins, in which one twin has developed Parkinson’s disease and the other has not. The first of this type of study was a retrospective analysis (Ward et al, 1984) in which 20 monozygotic twins (that is identical twins; they came from the same egg) were interviewed (Editor’s comment: isn’t it interesting to note that two individuals who are genetically identical can be affected differently by this disease). Personality-related questions were asked of the subjects at 8 and 16 years of age and then again 10 years after diagnosis of Parkinson’s disease. During all three periods the twin with Parkinson’s was more self-controlled than the non-affected twin.
Monozygotic Twins. Source: National Geographic
A similar study (Heberlein et al, 1998) which investigated 15 twins in which one of the pair was affected by Parkinson’s disease (6 monozygotic and 9 dizygotic/fraternal twins) found that affected twins showed higher inhibition and emotionality, and lower on extraversion than a set of control subjects (interestingly, they did not differ from their unaffected twin).
One very interesting study that has stemmed from this personality related research, focused on the idea that if people with Parkinson’s disease are more ‘inflexibility’ or ‘inhibited’, they may have trouble deceiving people. Taken another way: people with Parkinson’s may be more honest!
Here is the study I am referring to:
Title: Do parkinsonian patients have trouble telling lies? The neurobiological basis of deceptive behaviour.
Authors: Abe N, Fujii T, Hirayama K, Takeda A, Hosokai Y, Ishioka T, Nishio Y, Suzuki K, Itoyama Y, Takahashi S, Fukuda H, Mori E.
Journal: Brain. 2009 May;132(Pt 5):1386-95.
Using a novel cognitive task, the authors studied 32 patients with mild Parkinson’s disease of short duration and found that they had difficulty making deceptive responses when compared to healthy controls. That is to say, when the subject with Parkinson’s were commanded to lie, they had more trouble than healthy controls.
Parkinson’s subjects had trouble lying. Source: Abe et al, 2009
The authors then analysed the brains of the participants, using brain imaging techniques and found that this difficulty was significantly correlated with reduced metabolism in the prefrontal cortex – an area at the front of the brain where a lot of the higher-order (or executive) functioning of the brain is occurring.
The blue area indicating reduced metabolism in the prefrontal cortex. Source: Abe et al, 2009
While the study is very interesting, it can not determine whether this inability to lie (and the reduced metabolism in the prefrontal cortex) is personality-based or as a result of the disease course. This will require further investigation.
In summary, while it is fair to say that while some personality traits may appear to be associated with Parkinson’s disease, the results are controversial. Most of the studies have been conducted after diagnosis, and thus one can not be sure if the personality traits in question are really associated with the disease or simply a result of the disease. In addition, it may be that certain traits are associated with the disease, but it must be emphasised that being in possession of these traits does not necessarily mean you will develop Parkinson’s disease.