Environmental factors influencing the phenotype in identical t\vin sisters affected by hereditary idiopathic torsion dystonla

Among the affected subjects of a large family with several individuals presenting with adult-onset ITD, we observed two identical twin sisters. At the time of the study, they were 69-year-old. Twin 1 was the firstborn. Since she was a young girl, she used to carry on her head heavy bags. At the age of 65 she reported the onset of retrocollis. Dystonia rapidly progressed to the facial muscles, to the trunk, upper and, finally lower limbs: one year after the onset dystonia had become generalized. On examination, axial dystonia with retrocollis and irregular head tremor were the prominent signs; the patient was also invalidated by blepharospasm, adductor tremolous lanngeal dystonia and jauopening movements. Twin 2 was delivered few minutes after her twin sister; small for date; early development was normal. She did not use to carry heavies on her head, as she was very delicate. A; the age of 66 she first had involuntary movements of the pen-oral muscles. Later, dystonia progressed to the other facial muscles and to the neck. At the time of examination we observed blepharospasm and facial dystonia, tremolous voice, involuntary contractions of the platysma muscle, left SCM and trapezius involvement and bilateral tremor of the upper limbs. The role of environmental factors such as overuse or peripheral repetitive traumas on the expression of genetically programmed diseases is discussed.