The question of whether Parkinson's Disease is inherited is open to debate. American scientists recently claimed to have discovered a gene which is responsible for some cases, but the genetic contribution in most cases must be small. Balance may be affected, with frequent falls as patients find it difficult to correct a stumble. Rigidity resulting from a sustained increase in muscle contraction may cause pain, particularly at night in conjunction with leg or arm cramps. The handwriting becomes progressively smaller.
Constipation is also a common symptom.
In the advanced stages, the face appears fixed and mask like, there is difficulty with chewing and swallowing, dribbling occurs and speech becomes slow and monotonous. These may give an impression of stupidity or lack of interest, but Parkinson's disease alone does not cause loss of intelligence and sufferers can be as mentally agile as anyone else at their age. The rate of progression varies considerably and some people live for several years with only minor disabilities. Parkinson's disease does not normally shorten life. Because dopamine is depleted, there is a relative excess of acetylcholine.