Parkinson’s disease is likely to be a multifactor disorder involving a combination of environmental and genetics factors. The cause of PD is unknown. Various factors have been implicated in the etiology of the disease, such as infection, metabolic factors, free radicals, growth factors and toxins. Until recently research mainly focused on connection between this disorder and environmental factors such as viral infection and neurotoxins. In the last few years studies have shown linkage between genetic factors and movement disorders, because of this interest has shifted from environment to genome.
In 1997, a study funded by the National Institute of Health in the US reported that a family of Greek and Italian origin with a parkinsonian syndrome had an abnormal gene on chromosome 4 which produced a protien called alpha-synuclein. This family was atypical because of relatively young mean age of onset of 45 years and the rapid course of 10 years from the onset to death.
However, in over 200 familial cases of PD, studies by other groups, Parkinsonism was not linked to the abnormal gene on chromosome 4.
Work done by different groups have shown linkage of PD with other chromosomes 2 and 6. The demonstration of three different genes, on 3 different chromosomes, producing parkinsonism, shows that there are multiple causes even within genetic category. There are certainly multiple genetic causes but in all probability in majority of patients there are significant non-genetic causes.
It may be that there are several different environmental risk factors just as there are several different genes on several different chromosomes which establish the background of susceptibility to Parkinson’s disease. The liability to develop the disease will depend on what one might say the dose of environmental factor and the dose of genetic predisposition combined.