Update on pediatric dystonias: etiology, epidemiology, and management

Figures & data

Table 1 Classification of dystonias by etiology

Primary
• Primary pure	Dystonia is the only clinical sign (apart from tremor), and there is no identifiable exogenous cause or other inherited or degenerative disease
• Primary plus	Dystonia is a prominent sign but is associated with another movement disorder, for example myoclonus or parkinsonism. There is no evidence of neurodegeneration
• Primary paroxysmal	Dystonia occurs in brief episodes with normalcy in between. These disorders are classified as idiopathic (often familial although sporadic cases also occur) and symptomatic because of a variety of causes
Secondary	Dystonia is a symptom of an identified neurological condition, such as a focal brain lesion, exposure to drugs or chemicals
Heredodegenerative	Dystonia is a feature, amongst other neurological signs, of a heredodegenerative or metabolic disorder

Table 2 Classification of dystonias by age at onset

Early onset (variably defined as 20–30 years)	Usually starting in a limb and frequently spreading to involve other limbs and the trunk
Late onset	Usually starting in the neck (including the larynx), the cranial muscles or one arm. Tends to remain localized with restricted progression to adjacent muscles

Table 3 Classification of dystonias by distribution

Focal	Single body region
Segmental	Contiguous body regions
Multifocal	Noncontiguous body regions
Generalized	Both legs and at least one other body part
Hemidistonia	Half of the body

Table 4 Molecular classification of nonparoxysmal dystonias starting in children

Gene	Locus	Designation	Gene product	Type
With autosomal dominant inheritance
DYT1	9q34	Idiopathic torsion dystonia (ITD)	Torsin A (TOR1A)	Primary pure
DYT4	Unknown	Idiopathic torsion dystonia/whispering dysphonia	Unknown	Primary pure
DYT5	14q22.1	Deficit GTPCH	GTP-cyclohydrolase 1 (GCH1)	Primary plus
DYT6	8p11–21	Adolescent/early adult-onset	N-terminal THAP domain (THAP1)	Primary pure
DYT11	7q21 AD	Myoclonic dystonia	ε-sarcoglycan (SGCE)	Primary plus
DYT12	9q13 AD	Rapid-onset dystonia parkinsonism	Na^+/K^+-ATPase (ATP1A3)	Primary plus
DYT13	1p36.13–36.32	Early-onset dystonia with cranial cervical and upper limb involvement	Unknown	Primary pure
DYT15	18p11	Alcohol-responsive myoclonic dystonia	Unknown	Primary plus
With autosomal recessive inheritance
DYT16	2q31.2	Young onset dystonia-parkinsonism	Kinase PKR (PRKRA)	Primary plus
DYT17	20p11.22-q13.12	Autosomal recessive primary focal TD	Unknown	Primary pure
With X-linked inheritance
DYT3	Xq13.1	X-linked dystonia/parkinsonism	TATA-binding-protein-associated factor 1 (TAF1)	Primary plus
	Xq13	X-linked dystonia-deafness syndrome (Mohr-Tranebjaerg syndrome)	Mitocondrial import inner membrane translocase Tim8A (TIMM8A)