Neurologic Manifestations
All affected individuals reported to date have had episodes of choreiform, myoclonic, and/or dystonic movements that primarily affect the limbs, face, and/or neck. Typically the abnormal movements first appear during infancy, childhood, or early adolescence (range: neonatal period to age 19 years) [Chen et al 2015].
In those with milder manifestations, the abnormal movements involve the face and distal limbs (although minimally affecting function) and are socially debilitating. Some affected individuals may be described as "excessively clumsy."
In more severely affected infants, the earliest manifestations can include severe axial hypotonia resulting in developmental delays that lead to impairment in the ability to ambulate, requiring use of wheelchairs.
The abnormal movements are continual during waking hours, and have been noted to persist during sleep, particularly in infancy. Several affected individuals have noted severe, sleep-disrupting movements [Chen et al 2014, Chen et al 2015] that occurred during stages N2 and N3 of sleep, and were not associated with epileptiform discharges in one individual [Chen et al 2014].
A curious feature observed in some individuals is the occurrence of long periods (days to weeks) of remission.
The movements are often exacerbated by anxiety or stress and with drowsiness or sleep (although not by startle or alcohol). Less common triggers include intercurrent illness, fatigue, excitement, or caffeine, although one individual showed improvement with caffeine and other individuals have reported benefit [J Friedman, personal observation]. One woman reported that her choreiform movements were precipitated by enforced inactivity (e.g., as during a road trip), and could often be alleviated by voluntary movement.
Facial "twitches" (previously thought to be myokymia) involving the periorbital and/or perioral muscles may also be present. Twitches were also documented in limb muscles in one individual [Fernandez et al 2001].
Dysarthria and hypotonia have been reported in some affected individuals [Chen et al 2014, Chen et al 2015, Mencacci et al 2015].
Intellect and life span are usually normal. In severely affected individuals with onset in early childhood, intellectual disability may be present.
Neurologic examination can vary widely between individuals and in the same individual over time. Examination may reveal:
A mixed movement disorder that may include prominent choreiform movements usually affecting the hands and/or feet, often characterized as piano playing movements [
Vijiaratnam et al 2019];
Non-myokymic facial twitching, hyperreflexia of the lower limbs, and intermittent head or limb tremors [
Chen et al 2014];
Somatic mosaicism has been demonstrated in 43% of individuals with a de novo pathogenic variant [Raskind et al 2017] and in the founders of two multigenerational families, including one individual shown to be mosaic for the p.Met1029Lys variant who demonstrated considerable improvement during adulthood [Chen et al 2015].
Another individual, thought to be mosaic for p.Arg418Trp, exhibited significantly milder phenotypic features: fewer facial twitches, milder chorea, and no dysarthria [Mencacci et al 2015].
The natural history varies. In most, the abnormal movements are static or slowly progressive with increased severity and frequency. In some instances, choreiform movements have been more constant, and less paroxysmal, from the onset [Mencacci et al 2015]. The overall tendency is for the abnormal movements to stabilize in early middle age, at which point they may improve in some individuals.
Studies
Needle electromyogram (EMG) studies in two individuals with facial muscle twitching suggested centrally driven irregular muscle movements that were also observed in other muscles, including the orbicularis oculi, tongue, frontalis, and dorsal interosseous muscles. No fibrillations, fasciculations, myokymia, or myotonia were noted on EMG.
Brain imaging (MRI, CT) is normal.
Neuropathology. Gross pathology is normal. Detailed immunohistochemical analysis in one individual with molecularly confirmed ADCY5 dyskinesia revealed increased immunoreactivity for ADCY5 in multiple brain regions as well as tau deposits in deep cortical sulci, the midbrain and hippocampus. Lewy bodies and amyloid pathology were absent [Chen et al 2019].