Welcome to Healthcaremagic.
From your query i understood that you are worried about what to be the cause for your father's Progressive supranuclear palsy
Still the cause for this is under research.
But Scientists suspected few causes.
1. Unknown virus that may enter the body and it become active after many years then it cause signs and symptoms
2. Scientists found a abnormal protein clumps in brain called tau. It may be the cause for this disease.
ie. changes in normal gene in cell can damage entire cell and lead the disease.
4. Some free radicals ( ie. byproducts of energy production in our body) can cause injury to brain cells. this damage lead to symptoms and signs of the disease.
It is very difficult to find the specific cause of Progressive supranuclear palsy.
It is better to spend time in management of disease than further investigation.Parkinson
drugs carbidopa- levodopa and antidepressants are helpful.Physiotherapy
and psychological support is very essential.
Please follow Physician and neurologist
Hope this helps.