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A Genetic Abnormality Links Parkinsonís, Learning Disability and Schizophrenia

A genetic mutation that is a risk factor for cardiac anomalies, schizophrenia and learning disability may also be associated with the development of Parkinson’s disease (PD) at a young age, according to research reported in the May 2016 edition of Lancet Neurology. The mutation has other health consequences as well, and the study may have implications for the care of some people who develop PD younger than age 45.

There are many types of genetic mutations that are possible, one of which is a deletion (when a section of DNA is missing from a gene). Deletions are rare, but among them, one of the most common ones happens at a place called q11.2 on chromosome 22. This mutation, a 22q11.2 deletion, increases risk of schizophrenia and can cause cleft palate, heart defects. In about 90 percent of the cases, the deletion happens spontaneously in embryos and is not inherited.

Researchers previously noticed a higher-than-expected number of cases of PD among people who had a 22q11.2 deletion. But they weren’t sure how common it is in PD. So for the new study, scientists led by Nicholas W. Wood, M.D., Ph.D., at University College London, United Kingdom, searched for this association from the opposite direction — they looked for the chromosomal deletion among people with PD. To do so, the researchers screened genetic data collected during four earlier studies of 9,387 people with PD and 13,863 control subjects. They also analyzed the medical records of people with PD who had the 22q11.2 deletion.


Results

  • Of the 9,387 people with PD, 13 had a deletion in chromosome 22.
  • Researchers estimate that people with a 22q11.2 deletion have a risk of young-onset PD that is 20 times higher than the general population, similar to the increased risk for schizophrenia associated with the same mutation.
  • Among people with PD who had a 22q11.2 deletion, they developed the disease at the median age of 37 years. In contrast, the average age of PD onset for those without the deletion was 61 years.
  • Other than an earlier age of onset, PD symptoms were no different among people with the genetic deletion than among those without it.


What Does It Mean?

Young-onset PD itself is unusual, affecting five to 10 percent of people with PD. The proportion of those people with young-onset PD who also carry a 22q11.2 deletion is very small, less than one percent. The study authors urge clinicians to be alert to the possibility of this deletion among people with early-onset PD and to be aware of symptoms associated with the 22q11.2 deletion in order to manage other medical conditions associated with it and to better counsel patients.

Much remains to be learned about the 22q11.2 deletion and its relationship to PD. It may be that an as-yet-undiscovered gene that causes PD lies in the deleted region. Further research is needed to understand how this deletion links PD and schizophrenia. Both diseases involve the neurotransmitter dopamine — but schizophrenia is treated by lowering dopamine and PD is treated by raising it. Further investigating the 22q11.2 deletion could reveal clues to the underlying causes of both illnesses.


Reference: Mok KY, Sheerin U, Simón-Sánchez J, et al. (2016). Deletions at 22q11.2 in Idiopathic Parkinson’s Disease: A Combined Analysis of Genome-Wide Association Data. Lancet Neurology 15: 585-596 DOI: http://dx.doi.org/10.1016/S1474-4422(16)00071-5

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Source Date: Oct 26 2016