NEW YORK, May 25 (Reuters Health) - Mutations in the parkin gene can cause
Parkinson's disease to develop early in life, but the symptoms of this
early-onset form of the disease do not differ from the later developing illness.
Parkin gene mutations have only recently been linked to Parkinson's disease
in younger individuals, so the frequency of the mutations and the manifestations
of this form of the disease have not been studied previously, according to Dr.
Christoph Lucking from Hopital de la Salpetriere in Paris, France and an
international team of researchers.
The authors studied 73 families with early-onset, inherited Parkinson's
disease (including 152 affected family members), as well as 100 other patients
whose early-onset Parkinson's disease did not appear to be inherited.
Nearly half of the families with early-onset Parkinson's disease (PD) showed
mutations in their parkin genes, the authors report, whereas 18% of the patients
with isolated early-onset PD had parkin gene mutations. In both groups of
patients, two abnormal parkin genes appeared to be required for PD to develop.
Geneticists called such diseases autosomal recessive, meaning that an affected
gene is inherited from each parent.
Patients who carried abnormal parkin genes were younger when their disease
developed, and they were more likely to show abnormalities in muscle tone and
reflexes than their normal-parkin-gene counterparts, the report in the May 25th
issue of The New England Journal of Medicine indicates.
Once PD developed, patients with parkin gene mutations were more likely than
those without mutations to improve with medical therapy, the researchers note,
although they were also more likely to experience side effects from the drug
levodopa.
Despite these differences, the investigators suggest, physical examinations
and symptoms were not specific enough to be able to distinguish patients with
mutations from patients without mutations.
A wide variety of parkin genes was detected by specific testing, the
researchers say, but a relatively simple screening test should detect 70% of the
parkin mutations that cause Parkinson's disease.
"Mutations in the parkin gene are a major cause of early-onset autosomal
recessive familial Parkinson's disease and isolated juvenile-onset Parkinson's
disease (at or before the age of 20 years)," the authors conclude.
The results also suggest "...that among patients who are older than 30 years
at the onset of isolated (that is, not familial) Parkinson's disease, the
disease is mainly due to causes other than parkin mutations," the authors add.
