Placebo study could impact PKU clinical drug trials

Findings from a study published in the Oct. 23 edition of PLOS ONE, a peer-reviewed online scientific journal, suggests that people with a gene variation that leads to higher dopamine levels in the brain respond better to placebos than those individuals with low dopamine levels.

The science, health and technology news website LiveScience reported on the study and described how researchers tested to see whether a person’s genes can control a placebo response:

PKU, Phenylketonuria, Gene Mutation, Gene Variance, PKU Clinical Trials, Placebo

“To find out, Hall and her colleagues analyzed DNA from 104 patients with irritable bowel syndrome who were randomized to one of three groups: One was told they were on the waiting list for treatment, another received a placebo in the form of seemingly real, curt acupuncture, and the third group received fake acupuncture from a caring, warm practitioner who looked patients in the eye, asked about their progress, and even touched them lightly, Hall told LiveScience.

Patients with the high-dopamine version of the gene felt slightly better after seeing the curt, all-business health-care provider that gave placebo acupuncture. But they were six times as likely to say their symptoms improved with a caring practitioner as those with the low-dopamine gene, who didn’t improve much in any group.

The findings suggest that medical studies called clinical trials could identify treatment versus placebo effect by grouping patients by gene variant, Hall said. Knowing up front the level of placebo effect for a clinical trial could reduce the cost of the trial significantly by using fewer participants, for instance, she said.”

How does this relate to PKU?

PKU patients have very little or no phenylalanine hydroxylase (PAH), an enzyme in the body that converts phenylalanine into tyrosine. Tyrosine is used by the brain to synthesize dopamine, an important neurotransmitter involved in motor functions and mood. This means that PKU patients, especially those “off-diet” or those not regularly consuming formula, will experience relatively low levels of dopamine. This is the reason that some of the side effects experienced by PKU patients on an uncontrolled diet can include anxiety, depression and other mood disorders.

No doubt, it will be interesting to see whether these new findings will have any impact on how BioMarin or other pharmaceutical companies will structure future PKU clinical trials. Researchers will have to consider whether having a mixture of on-diet and off-diet PKU patients randomly assigned to control and experimental groups will have any bearing on the trial’s accuracy. Or perhaps a closer look at the specific gene mutation that allows some individuals to operate with higher dopamine levels will someday provide answers for how to increase dopamine in those of us who could benefit from a little more.


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