WASHINGTON – Women who develop Parkinson's disease do so at an older age than affected men, are more likely to present with a tremor-dominant form, and have higher levels of striatal dopamine transporter, according to data presented at the World Parkinson Congress.
“Several findings in our study indicated a more benign phenotype for women with Parkinson's disease,” said Dr. Charlotte Haaxma of Raboud University in Nijmegen, the Netherlands.
Dr. Haaxma and her colleagues retrospectively studied 253 patients with Parkinson's disease (PD) seen at their clinic between 1988 and 2003 to assess gender differences. Men accounted for 62% of patients. Patients were excluded from the study if they were taking levodopa or another dopamine agonist, had the disease for longer than 10 years, had physical disabilities resulting from another disease, used non-PD drugs, or were demented.
The researchers assessed the age at onset, presenting symptoms, estrogen status, Unified Parkinson Disease Rating Scale (UPDRS) motor scores, and dopamine transporter levels measured by [I-123]FP-CIT single-proton emission computer tomography (SPECT) imaging. UPDRS motor scores were assessed every 3–6 months.
Women were slightly older at the age of onset (53 years) than men (51 years). Women were also more likely to present with tremor–67% vs. 48%. “This gender difference remained intact throughout all age categories,” said Dr. Haaxma.
This finding prompted the researchers to look more closely at patients with tremor as the presenting symptom. Patients who presented with tremor were on average age 55 years at onset, compared with patients who presented with bradykinetic rigidity (age 50 years at onset).
“Women were older at symptom onset. They presented more often with tremor, and, if so, had an even higher age at onset,” said Dr. Haaxma. In addition, “the more children that a woman had, the higher the age at onset–2.7 years later per child,” said Dr. Haaxma. Women also had onset 0.5 year later for each fertile year. No correlations were found for age of menarche or estrogen therapy with age at onset.
Mean UPDRS motor scores were comparable for both genders at onset and the rate of degeneration did not differ between genders. However, tremor-dominant patients had a 38% slower rate of UPDRS motor score decline than bradykinetic-rigid subtype patients.
In terms of [I-123]FP-CIT SPECT imaging, women had a 16% higher mean binding than men, indicating higher striatal levels of dopamine transporter. However, the rate of dopamine transporter loss did not differ between genders. The tremor-dominant group tended to have a slower rate of deterioration, though this trend did not reach statistical significance.
The researchers proposed two hypothetical models to interpret the findings. In the first model, women have higher dopamine striatal levels and therefore take longer to reach the point of symptom onset. “Further, the estrogen effect of parity and other items associated with high cumulative estrogen levels might … delay the moment of symptom onset further,” said Dr. Haaxma.
In the second model, women have a slower rate of progression, so they take longer to reach symptom onset. Estrogen effects would translate into an even slower rate of decline. However, once symptoms start, the estrogen effect decreases, and men and women deteriorate with similar speed.