There is no family history of Parkinson's disease. What is the correct factor in this case?

You are attending a 70-year-old man recently treated for Parkinson’s disease, to which treatment he has been
showing good response.
His son wants to know how likely he is to develop Parkinson’s disease. There is no family history of
Parkinson’s disease.
What is the correct factor in this case?

Inheritance pattern of this disease is not known This is the correct answer
It all depends on the exposure to the environmental factors
Late onset disease is not usually familial
The disease is autosomal dominant
The disease is autosomal recessive

Parkinson’s disease is a common neurodegenerative disorder which selectively affects dopaminergic neurons
of the substantia nigra, cultimating in their destruction. After approximately 50% of the dopamine neurones, and
75-80% of striatal dopamine is lost patients start to exhibit the classical signs of bradykinesia, resting tremor
and rigidity.
Despite many years of research, the cause of Parkinson’s disease is not fully understood. The relative
contribution of genetic and environmental factors still remains unclear. Early studies showed that protoxin nmethyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes parkinsonism in animals and humans. Other
environmental toxins have also been linked, but there is no clear causation between exposure and disease.
Up until 10 years ago, it was widely thought that Parkinson’s disease was not a genetic disorder. However,
since then inherited forms have been identified and there have been a number of genetic findings culminating
in the cloning of several genes from loci which have been given the nomenclature PARK1 to PARK 12. α -
synuclein is thought to be an important moleceule in the dopaminergic signalling pathways.
In addition single genes have been linked to heritable forms of Parkinson’s disease, including SNCA, Parkin,
PINK1, DJ1 and LRRK2. The inheritance pattern differs depending on the gene that is altered: LRRK2 and
SNCA mutations are autosomal dominant; PARK2, PARK7 and PINK1 are autosomal recessive.
Despite the identification of these genes, the majority of the cases remain idiopathic and therefore the correct
answer is option A.