According to Yue Huang and her team from the University of New South Wales, Sydney, Australia, Parkinson's disease is marked by the abnormal accumulation of a-synuclein NACP-Rep1 and the early loss of dopamine neurons in the substantia nigra region of the brain.
A polymorphism in the promotor of NACP-Rep1 has been implicated as a risk factor for the disease.
"Our data are the first to show that polymorphisms of NACP and MAPT interact to influence the rate of progression of Parkinson's disease, a finding with clinical utility," Huang said.
"Our study shows that genotypes for NACP and MAPT can be used as a surrogate marker for the estimated rate of Parkinson's disease progression, with positive predictive values of 94-100 percent for certain genotypes," she said.
123 patients with Parkinson's disease underwent genetic testing to determine NACP-Rep 1 and MAPT H1 allele or genotype. The patient's disease severity was measured using the Unified Parkinson's Disease Rating Scale (UPDRS), and a measurement of disease progression was calculated based on detailed information about disease and symptom onset.
Three common variations, or alleles, of NACP-Rep1 were detected. Patients with one '0' NACP-Rep1 allele had significantly slower disease progression compared to two or no '0' carriers.
This may partially reflect the known protective influence of '0' allele on Parkinson's disease. There was a high variation in the estimated rate of disease progression for the '0' allele group due to an interactive effect with the MAPT genotype.
The results of the study showed that a low relative risk for rapid clinical progression in patients with one NACP-1 '0' allele, or those carrying MAPT non-H1H1 genotype with two NACP-Rep1 '0's. In contrast there was a high risk of a fast clinical progression in patients carrying MAPT H1H1 genotype with two or no NACP-Rep1 '0's.
"Based on current knowledge, it is perhaps not surprising that genetic variation predisposing to high a-synuclein expression gives rise to more rapid progression of PD," Huang said.
"However, our results suggest that low a-synuclein expression may also be as detrimental in people with high tau expression levels, calling into question the concept that reducing neuronal a-synuclein in all PD patients may be therapeutically advantageous," she added.