Trihexyphenidyl (THP,  benzhexol, trihex, marketed as Artane and others) is an antispasmodic drug used to treat stiffness, tremors, spasms, and poor muscle control. It is an agent of the antimuscarinic class and is often used  in management of Parkinsons disease. It was approved by the FDA for the treatment of Parkinsons in the US in 2003.It is on the World Health Organizations List of Essential Medicines. Medical uses
Trihexyphenidyl is used for the symptomatic treatment of Parkinsons disease in mono and combination therapy. It is active in postencephalitic, arteriosclerotic, and idiopathic forms. The drug is also commonly used to treat extrapyramidal side effects occurring during antipsychotic treatment. It reduces the frequency and duration of oculogyric crises as well as of dyskinetic movements and spastic contractions. Trihexyphenidyl may improve psychotic depression and mental inertia frequently associated with Parkinsons disease and symptomatic problems caused by antipsychotic treatment.The drug cannot cure Parkinsons disease, but may provide substantial alleviation of symptoms. An estimated 50–75% of people with Parkinsons disease will react positively and experience a 20–30% symptomatic improvement. To increase therapeutic activity, trihexyphenidyl is often given concomitantly with levodopa or other antimuscarinic or antihistaminic (e.g. diphenhydramine) agents. Combination therapy with dopamine agonists such as cabergoline is also possible. This is often termed a multidimensional approach. It has also been prescribed for essential tremor and akathisia.
The loss of other genes in the deleted region may help explain why the features of Smith–Magenis syndrome vary among affected individuals. A small percentage of people with Smith–Magenis syndrome have a mutation in the RAI1 gene instead of a chromosomal deletion. These deletions and mutations lead to the production of an abnormal or nonfunctional version of the RAI1 protein. RAI1 is a transcription factor that regulates the expression of multiple genes, including several that are involved in controlling circadian rhythm, such as CLOCK. The groups led by James Lupski (Baylor College of Medicine) and Sarah Elsea (Virginia Commonwealth University) are in the process of studying the exact function of this gene in relation to Smith Magenis Syndrome.SMS is typically not inherited. This condition usually results from a genetic change that occurs during the formation of reproductive cells (eggs or sperm) or in early fetal development. People with Smith–Magenis syndrome most often have no history of the condition in their family. Diagnosis
SMS is usually confirmed by blood tests called chromosome (cytogenetic) analysis and utilize a technique called FISH (fluorescent in situ hybridization). The characteristic  micro-deletion was sometimes overlooked in a standard FISH test, leading to a number of people with the symptoms of SMS with negative results. The recent development of the FISH for 17p11.2 deletion test has allowed more accurate detection of this deletion. However, further testing is required for variations of Smith–Magenis syndrome that are caused by a mutation of the RAI1 gene as opposed to a deletion.