The genetics of idiopathic torsion dystonia.

The genetics of idiopathic torsion dystonia N A Fletcher Idiopathic torsion dystonia (ITD) is a disorder of the central nervous system which produces dystonic movements and postures.The spectrum of severity is wide, including severe generalised dystonia (formerly termed dystonia musculorum deformans), segmental dystonia, and focal dystonias such as torticollis, blepharospasm, and writer's cramp (table).No other neurological deficits occur in ITD, although some patients display a postural tremor that is clinically indistinguishable from essential tremor.1Although ITD is frequently inherited,2 the genetics of the condition have only recently become clear after decades of controversy.This disorder is not rare; the most recent estimate ofprevalence (from the United States) is approximately 1 in 30003 and a strikingly high frequency among Ashkenazi Jews has long been apparent.4I ITD may develop at almost any age and this is the key factor determining its severity; generalised ITD almost always starts before the age of 20 years whereas focal Classification of dystonia by anatomical extent.Focal: one body part affected, examples include: Blepharospasm (eyes) Torticollis (neck) Oromandibular dystonia Spasmodic (adductor) laryngeal dystonia Whispering (abductor) laryngeal dystonia Writer's cramp (arm) Segmental: two or more contiguous parts affected: Cranial: 2 or more parts of cranial or neck musculature affected Brachial: 1 arm + axial (neck or trunk) or 2 arms ± axial (neck or trunk) affected Axial: neck + trunk affected Crural: 1 leg + trunk or both legs ± trunk Generalised: segmental crural plus any other part affected Multifocal: 2 or more non-contiguous areas affected.Hemidystonia: ipsilateral arm and leg affected.ITD usually begins in older adults.Some adult onset cases are very mild and often asymptomatic.6The