Clinical Description
DRPLA (dentatorubral-pallidoluysian atrophy) is a progressive neurologic disorder characterized by five cardinal features (irrespective of the age of onset): ataxia, cognitive decline, myoclonus, chorea, epilepsy, and psychiatric manifestations [Ikeuchi et al 1995b, Kanazawa 1998]. Clinical manifestations vary by age of onset, which is inversely related to ATN1 CAG repeat size [Ikeuchi et al 1995b, Komure et al 1995].
Onset ranges from infancy to late adulthood (range: age 0-72 years; mean: age 31.5 years). Juvenile onset (before age 20 years) is characterized by myoclonus, epilepsy, and progressive intellectual deterioration, whereas adult onset (after age 20 years) is characterized by ataxia, choreoathetosis, and dementia or neuropsychiatric changes. Disease duration is on average eight years (range: 0-35 years) and age at death is on average 49 years (range: age 18-80 years) [Hasegawa et al 2010].
Juvenile Onset (Before Age 20 Years)
Juvenile-onset (also referred to as childhood- or early-onset) DRPLA is generally associated with ≥65 CAG repeats. Juvenile onset is typically characterized by developmental delay, progressive intellectual disability, myoclonus, and epilepsy, often referred to as a progressive myoclonic epilepsy (PME) phenotype [Kanazawa 1998, Hasegawa et al 2010, Maruyama et al 2012, Carroll et al 2018].
Developmental delay and intellectual disability are the most common initial manifestations, with a mean age of onset of 7.1 ± 4.8 (range: 2-18) years [Egawa et al 2008, Maruyama et al 2012]. Variable findings are developmental regression, attention-deficit/hyperactivity disorder, autism spectrum disorder, and microcephaly [Licht & Lynch 2002, Shahwan et al 2005].
Seizure types vary and are frequently resistant to anti-seizure medication [Koide et al 1994, Ikeuchi et al 1995b, Egawa et al 2008]. Clinical-electrographic focal-onset seizures with altered alertness are frequently seen, with higher prevalence when epilepsy onset is before age 10 years [Egawa et al 2008]. Seizure types may evolve over time. Partial seizures and brief generalized seizures (atypical absence and myoclonic seizures) may be seen earlier and generalized tonic-clonic seizures later in the disease course [Egawa et al 2008]. Common findings are photosensitivity with reflex seizures triggered by visual stimuli and EEG photoparoxysmal response to intermittent photic stimulation.
Ataxia may occur early in the disease course or develop later. Eventually, chorea and psychiatric manifestations may also develop [Hasegawa et al 2010, Maruyama et al 2012].
Adult Onset (After Age 20 Years)
Adult-onset (also referred to as late-onset) DRPLA is generally associated with <65 CAG repeats. In one series, the mean age of onset was 48 years [Hasegawa et al 2010]. The most prominent clinical features are ataxia and/or choreoathetosis, combined with personality changes with or without cognitive decline [Kanazawa 1998]. In some individuals, involuntary movements and dementia may mask the presence of ataxia.
Behavioral impairment is characterized by delusions, hallucinations, depressed mood, apathy, loss of inhibitory control, poor judgment, impulsivity, irritability, and aggression [Adachi et al 2001, Grimaldi et al 2019]. This clinical picture may cause psychiatric hospitalization and complicate the differential diagnosis, particularly in younger adults. Cognitive decline is characterized by deterioration of attention and executive functions, semantic fluency, and visuoconstructive abilities; memory is relatively preserved in all its components [Lindsay & Storey 2017, Grimaldi et al 2019].
Rarely, seizures may be present in individuals with disease onset between ages 20 and 40 years. Older individuals (especially those older than age 60 years in one series) may present with isolated ataxia and/or ataxia combined with dementia [Sugiyama et al 2018].
The severity and frequency of sleep disturbances in DRPLA are probably underestimated. Insomnia, excessive daytime sleepiness, and circadian rhythm disturbance can occur. In a case report by Kim et al [2018], a family with DRPLA presented with REM sleep behavior disorders (RBD) in the absence of more common sleep-related respiratory issues such as sleep apnea or hypopnea. In some members of this family, RBD appeared before the classic clinical manifestations of DRPLA.
Other clinical manifestations that may be present in adult-onset DRPLA irrespective of the actual age of onset include choreoathetosis, dystonia, myoclonus, oculomotor impairments, postural instability, corneal endothelial degeneration, and optic atrophy [Warner et al 1995, Destée et al 2000, Ito et al 2002, Hatano et al 2003, Wardle et al 2008, Vale et al 2010, Silver et al 2015, Grimaldi et al 2019].
Dysphagia is frequently seen in the late stages of disease [Hasegawa et al 2010].
Other clinical manifestations rarely reported include parkinsonism, tremors, hyperreflexia, and posterior column sensory loss [Shimojo et al 2001, Licht & Lynch 2002, Rajput 2011].
All Ages
Neuroimaging. Typical MRI findings include atrophic changes in the cerebellum and brain stem, in particular the pontine tegmentum. Quantitative analyses reveal that both the age at MRI and the size of the expanded CAG repeat correlate with the atrophic changes.
Cerebellar white matter lesions are also described in individuals with late adult-onset and elderly-onset disease, often in the paravermal areas (medial part of the cerebellar hemispheres adjacent to the vermis) and present as high-intensity signals in MRI FLAIR images. Although paravermal lesions are considered typical of DRPLA and lacking in other autosomal dominant spinocerebellar ataxias, they are not specific to DRPLA and can be present in adult-onset neuronal intranuclear inclusion disease and fragile X-associated tremor/ataxia syndrome [Sugiyama et al 2018, Sugiyama et al 2020].
Diffuse high-intensity areas deep in the white matter are often observed on T2-weighted MRI in individuals with adult-onset DRPLA of long duration [Koide et al 1997].
Using 18F-fluorodeoxyglucose positron emission tomography (18F-FDG-PET), bistriatal glucose hypometabolism was reported in two affected individuals with juvenile-onset DRPLA; this was not present in individuals with adult onset [Sone et al 2016].
Neuropathology. The major neuropathologic changes are combined degeneration of the dentatorubral and pallidoluysian systems. Also described are cerebral white matter damage, including diffuse myelin pallor, axonal preservation, and reactive astrogliosis with only mild atherosclerotic changes [Muñoz et al 2004].
Histologically, as in other polyglutamine diseases, neurons show intranuclear inclusions [Mori et al 2012a, Mori et al 2012b].
Genotype-Phenotype Correlations
Heterozygotes. In general, an inverse correlation exists between the age at onset and the size of the expanded ATN1 CAG repeat [Koide et al 1994, Ikeuchi et al 1995b] (see Table 2).
Note: ATN1 CAG repeat ranges overlap and the distinctions are not clearly defined.
Table 2.
Correlation between Age at Onset and Size of ATN1 Repeat
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Age at Onset | ATN1 CAG Repeat Range |
---|
<21 years | 63-79 |
21-40 years | 61-69 |
>40 years | 48-67 |
Because juvenile onset (before age 20 years) is associated with the progressive myoclonus epilepsy (PME) phenotype and adult onset (after age 20 years) with the non-PME phenotype, the clinical presentation is strongly correlated with the size of expanded CAG repeats. The frequency of signs and symptoms in affected individuals with <65 CAG repeats and those with ≥65 CAG repeats were summarized by Hasegawa et al [2010].
Severe infantile onset with an extreme ATN1 CAG expansion of 90-93 CAG repeats (c.1462CAG[90_93]) has been reported [Shimojo et al 2001].
Homozygotes
An individual with relatively small biallelic expanded
ATN1 CAG repeat expansions had symptom onset at age 14 years, indicating a possible dosage effect [
Sato et al 1995].
An individual of Japanese ancestry homozygous for a 57-CAG repeat expansion was born to consanguineous parents. Early onset (around age 18 years) and more severe manifestations were observed [
Ikeuchi et al 1995b].
Prevalence
DRPLA is more prevalent in populations of Japanese ancestry, where it affects 0.2-0.7 in 100,000 people [Takano et al 1998, Tsuji et al 2008]. The Japanese population has a greater number of individuals with 20-35 CAG repeats than populations of European origin [Takano et al 1998]. A nationwide epidemiologic study showed that DRPLA is the third most common autosomal dominant ataxia, accounting for 9.7% of cases in Japan [Tsuji et al 2008]. In another Japanese study, DRPLA was the most common cause of childhood-onset cerebellar ataxia [Ono et al 2019].
DRPLA is thought to occur at much lower rates in non-Japanese populations; however, it has also been reported in North America, South America, Europe, and Australia (for a summary of all cases reported see Chaudhry et al [2021]). The frequency of DRPLA has been estimated in cohorts with mostly cerebellar ataxia of unknown cause, typically with a pattern of autosomal dominant inheritance, in the following countries/regions:
Italy: 1% [
Filla et al 2000]. A study of the largest northern European DRPLA pedigree, originating in Italy in the 1500s with a founder couple, demonstrated that DRPLA can be observed over time in certain geographic areas [
Grimaldi et al 2019], suggesting that prevalence could be higher than expected in non-Asian populations.
Portugal: 2%-11.2% [
Silveira et al 2002,
Vale et al 2010]. In the Portuguese population, the prevalence of DRPLA was estimated at 0.33 in 100,000 people, ranking as the second most frequent autosomal dominant ataxia [
Coutinho et al 2013]. The prevalence in Portugal is almost comparable to Japan, and is higher than that described for the rest of Europe. The Portuguese families with DRPLA share the same haplotype as in Japan [
Martins et al 2003], which could explain the higher prevalence in this country.
South Wales: 11.4% [
Wardle et al 2008]. In South Wales the theory of a founder effect only accounted for some but not all of the high prevalence of DRPLA, as the Japanese haplotype was only detected in three out of four families [
Wardle et al 2008]. These findings suggested that DRPLA prevalence can also be influenced by spontaneous repeat expansions in families with high-normal repeats.