A new study of twins has found that trichloroethylene, or TCE, a solvent widely used in refrigerants and as a metal degreaser, is associated with an increased risk of Parkinson's disease.

The analysis, published Monday in The Annals of Neurology, used data from an American military twin registry to examine 99 twin pairs, average age 65, in which only one sibling had Parkinson's. A questionnaire was used to establish the twins' history of jobs and hobbies that would have exposed them to TCE.

A twin who had worked with TCE was more than six times as likely to have Parkinson’s as one who had not, the researchers found. Twins exposed to two other solvents, perchloroethylene and carbon tetrachloride, substances used in dry cleaning and other industries, also had a slightly higher risk of developing Parkinson’s.

The authors acknowledge that it is difficult to collect accurate information on exposure retrospectively, that the study is small, and that it is limited to occupational exposure. Still, the lead author, Dr. Samuel M. Goldman of the Parkinson’s Institute, said that almost everyone is exposed to these substances. “These are common contaminants,” he said. “They are detected in blood, breast milk, water and food.”

According to Dr. Goldman and his colleagues, 50 million pounds of TCE are released annually into the environment in the United States.

It is becoming generally known that Parkinson's disease influences more than a patient's motor functions. Patients often also suffer from depression, fear and incontinence, for example. However, the disease also undermines the language processing ability.

University of Groningen researcher Katrien Colman has found clear indications of this in Dutch native speaker patients. She will be awarded a PhD by the University of Groningen on 17 February 2011. Colman: 'We could spare patients a lot of suffering if we learn to better understand their language processing problems.'

The more the population ages, the more cases there will be of Parkinson's disease. The general public mainly recognizes Parkinson's through its motor symptoms. Patients have trembling hands or arms, stiff limbs and walk bent over, shuffling. Well-known patients included Prince Claus, consort to Queen Beatrix of the Netherlands, and Pope John Paul II.

Stiff limbs

Parkinson's disease is caused by a shortage of dopamine in the brain. A lack of this neurotransmitter leads not only to the familiar motor symptoms, but also affects the executive brain functions of the patient; in other words, their ability to guide their own behaviour in new, non-routine situations. Examples include systematic actions, foreseeing consequences and resolving problems flexibly.

Stilted sentences

Katrien Colman demonstrated that impairment of the executive functions also affects language processing. For example, impairment of the executive brain function can result in a patient no longer understanding a complicated sentence construction: before the patient reaches the end of the sentence, he or she has forgotten how it began. Impairment of flexibility means that the patient has difficulty in changing the subject, even if there is a clear reason to do so. Impairment of the ability to work in a structured way means that it becomes difficult to construct grammatically correct sentences.

Aphasia: a different problem

The language processing problems of Parkinson's patients are sometimes compared with those of aphasia patients -- often incorrectly, as revealed by Colman's research. Aphasia, for example as the result of an infarct, can affect the grammatical ability itself, meaning that the patient can no longer conjugate a verb. The patient can then, for example, no longer derive the past participle 'walked' from the infinitive 'to walk'. With Parkinson's patients, this specific grammatical ability is not affected but rather the underlying executive function. The patient is then in principle able to derive a past participle, but in some situations does not do so -- for example because he can no longer view the sentence as a whole.

The research reveals that the language processing problems of Parkinson's patients deserve serious attention. Colman said, 'If communication is difficult, this does not necessarily mean that the patient is tired or depressed, or that there's something wrong with his intelligence.' Patients can be helped if people communicate with them in simple sentences, but it would be wrong to treat them as children. Colman: 'We could spare patients a lot of suffering if we learnt to better understand their language impairments and developed suitable ways to communicate with them.'

Black patients and those with lower levels of income and education have more severe parkinsonism with greater levels of disability, a new study FINDS.

Parkinsonism -- a condition marked by slow movements, tremor and rigidity -- is common among older adults in the United States. Parkinson's disease is the most common cause of parkinsonism.

This study by researchers at the University of Maryland, Baltimore included 1,159 patients with parkinsonism. Of those patients, 93.4 percent were white, 6.1 percent were black, 61.2 percent earned more than $50,000 a year, 62.7 percent had completed college, and 79.2 percent had been diagnosed with Parkinson's disease.

Black patients tended to have more severe parkinsonism and greater levels of disability than white patients. Patients with lower levels of income and education were also more likely to have greater disease severity and disability.

The study also found that black patients were prescribed fewer medications to treat parkinsonism at their first clinic visit than white patients -- 61.9 percent vs. 77.6 percent.

Only 20.6 of black patients were prescribed newer dopaminergic medications (drugs that replace the neurotransmitter dopamine), compared with 41.1 percent of white patients. Antipsychotic drugs were prescribed to 12.7 percent of black patients and 6.1 percent of white patients. There was no disparity in medication treatment, however, tied to income and education levels.

"Parkinsonism reduces quality of life and results in disability and premature mortality [death]. The results of this study suggest we need to better understand the cause of parkinsonism and to find remedies for disparate outcomes among patients with parkinsonian disease who are of different backgrounds and means," the researchers concluded.

The study appears online Dec. 13 and in the April 2011 print issue of the Archives of Neurology.