Most published research on<unk>  originates in the United States; in international<unk>  research, the Diagnostic and Statistical Manual of Mental Disorders (DSM) is preferred over the World Health Organization (WHO) classification, which is criticized in the 2021 European Clinical Guidelines. In the fifth version of the DSM (DSM-5), published in 2013,<unk>  is classified as a motor disorder (a disorder of the nervous system that causes abnormal and involuntary movements). It is listed in the neurodevelopmental disorder category.<unk> 's is at the more severe end of the spectrum of tic disorders; its diagnosis requires multiple motor tics and at least one vocal tic to be present for more than a year. Tics are sudden, repetitive, nonrhythmic movements that involve discrete muscle groups, while vocal (phonic) tics involve laryngeal, pharyngeal, oral, nasal or respiratory muscles to produce sounds. The tics must not be explained by other medical conditions or substance use. Other conditions on the spectrum include persistent (chronic) motor or vocal tics, in which one type of tic (motor or vocal, but not both) has been present for more than a year; and provisional tic disorder, in which motor or vocal tics have been present for less than one year. The fifth edition of the DSM replaced what had been called transient tic disorder with provisional tic disorder, recognizing that "transient" can only be defined in retrospect. Some experts believe that<unk>  and persistent (chronic) motor or vocal tic disorder should be considered the same condition, because vocal tics are also motor tics in the sense that they are muscular contractions of nasal or respiratory muscles.<unk>  is defined only slightly differently by the WHO; in its ICD-11, the International Statistical Classification of Diseases and Related Health Problems,<unk>  is classified as a disease of the nervous system and a neurodevelopmental disorder. Older versions of the ICD called it "combined vocal and multiple motor tic disorder de la<unk> ". Genetic studies indicate that tic disorders cover a spectrum that is not recognized by the clear-cut distinctions in the current diagnostic framework. Since 2008, studies have suggested that<unk> 's is not a unitary condition with a distinct mechanism, as described in the existing classification systems. Instead, the studies suggest that subtypes should be recognized to distinguish "pure<unk> " from<unk>  that is accompanied by attention deficit hyperactivity disorder (ADHD), obsessive–compulsive disorder (OCD) or other disorders, similar to the way that subtypes have been established for other conditions, such as type 1 and type 2 diabetes. Elucidation of these subtypes awaits fuller understanding of the genetic and other causes of tic disorders
Tourette syndrome
Lesch–Nyhan syndrome
Conduct disorder
Tardive dyskinesia  Tardive dyskinesia  1
Autism spectrum
High-functioning autism
Oppositional defiant disorder
Klismaphilia