Clinical Description
The spectrum of DCTN1-related neurodegeneration includes Perry syndrome, distal hereditary motor neuronopathy type 7B (dHMN7B), frontotemporal dementia (FTD), motor neuron disease / amyotrophic lateral sclerosis (ALS), and progressive supranuclear palsy. Some individuals present with overlapping phenotypes (e.g., FTD-ALS, Perry syndrome-dHMN7B) [Caroppo et al 2014, Konno et al 2017, Zhang et al 2021]. In most families, the phenotype is consistent among affected family members. However, not infrequently, the same DCTN1 pathogenic variant may manifest with a different clinical phenotype even within the same family.
Perry Syndrome
The cardinal signs of Perry syndrome are parkinsonism, neuropsychiatric symptoms, hypoventilation, and weight loss [Konno et al 2017, Mishima et al 2018]. The mean age of onset is 49 years (range: 35-70 years); the mean disease duration is five years (range: 2-14 years). Psychiatric (depression, apathy, character changes, withdrawal) and motor (parkinsonism) symptoms tend to occur early, whereas severe weight loss and hypoventilation manifest later. In most affected persons, the reported cause/circumstance of death relates to sudden death/hypoventilation or suicide [Konno et al 2017, Mishima et al 2018, Tsuboi et al 2021].
Parkinsonism. Most individuals with Perry syndrome present with parkinsonism, which manifests in rigidity (60%), tremor (52%), bradykinesia (38%), and postural instability (28%). It is relatively symmetric and less responsive to levodopa than that found in Parkinson disease. Some individuals may develop complications of levodopa therapy, including fluctuations and peak dose dyskinesia [Konno et al 2017, Mishima et al 2018].
Hypoventilation. Alveolar hypoventilation manifests particularly at night or during sleep, with tachypnea alternating with normal respiratory cycles, leading to frequent awakenings. Polysomnographic recordings show that hypoxemia and hypercapnia are of central origin; that is, there is no obstructive or structural respiratory tract abnormality. Respiratory symptoms present later in the disease course and slowly worsen over time, leading to respiratory insufficiency and death. However, respiratory failure may occur rapidly without any predictive signs. Of note, hypoventilation was not reported in four of the thirty-one families with confirmed Perry syndrome [Konno et al 2017, Mishima et al 2018, Tsuboi et al 2021].
Sleep difficulties occur in approximately 20% of individuals and probably reflect hypoventilation.
Neuropsychiatric findings. Depression and apathy occur in the majority of affected individuals and are the most common initial presentation. Depression is usually more severe than that observed in Parkinson disease, refractory to treatment, and often associated with suicidal ideations. Apathy is manifested by social withdrawal, loss of interest, and "psychic self-activation" (referred to as "athymhormia" in French literature). Cognitive impairment is associated with the frontostriatal pattern of deficits. In addition, some individuals present with disinhibited behavior, impulsivity, and other psychiatric features overlapping with the behavioral variant of FTD (bvFTD) [Konno et al 2017, Mishima et al 2018, Milanowski et al 2020].
Weight loss is observed in 50% of individuals, progression can vary. The etiology is probably multifactorial, with dysphagia and psychiatric comorbidities being the leading causes; however, a disease-specific mechanism involving central modification of hunger sensation or an increase in metabolic rate cannot be excluded [Konno et al 2017, Mishima et al 2018].
Autonomic failure (e.g., erectile dysfunction, orthostatic hypotension, bladder and bowel incontinence, anhidrosis) has been reported in some individuals; however, it is probably underreported as no information on autonomic function is provided in most reports.
Other Phenotypes
Distal hereditary motor neuronopathy type 7B (dHMN7B) is a length-dependent, primarily motor neuropathy [Hwang et al 2016, Zhang et al 2021]. In most individuals it presents between the third to fifth decades, but it can manifest earlier, even at birth. It is characterized by bilateral vocal cord palsy (leading to breathing difficulties) and progressive atrophy and weakness of the facial and distal limb muscles [Hwang et al 2016, Tian et al 2020, Zhang et al 2021]. However, the clinical presentation varies, and not all features may be present [Zhang et al 2021].
DCTN1-related
frontotemporal dementia (FTD) is characterized by the impairment of frontal and temporal lobe functions [Convery et al 2019, Piguet & Kumfor 2020]. FTD can be broadly divided into behavioral (bvFTD) and language (lvFTD) variants. Individuals with bvFTD present with predominant behavioral and personality changes, whereas those with lvFTD develop worsening of speech and language. BvFTD manifests with apathy, disinhibition, impulsivity, loss of empathy, obsessive behaviors, alterations in food preferences, executive function deterioration, and lack of insight. LvFTD, also called primary progressive aphasia, is characterized by gradually progressive disorders of speech and language that disturb the activities of daily living and may be accompanied at later stages by behavioral symptoms similar to those observed in bvFTD [Convery et al 2019]. To date, most individuals with DCTN1-related FTD have presented with bvFTD.
DCTN1-related motor neuron disease or amyotrophic lateral sclerosis (ALS) is a multifaceted neurodegenerative disorder predominantly affecting the motor system. It typically presents in adulthood with weakness and atrophy of the distal limb muscles that gradually spread to adjacent body regions. Muscle weakness and atrophy are often associated with fasciculations, muscle cramps, and stiffness. However, the age and region of onset are variable, and in some individuals the disease may start with bulbar symptoms [Masrori & Van Damme 2020]. Additionally, non-motor symptoms are increasingly recognized, including mood disturbances (depression, anxiety), cognitive decline (most pronounced in executive functions), behavioral symptoms (most commonly apathy and disinhibition), suicidal ideation, pseudobulbar affect, sleep disruption, autonomic dysfunction (bladder incontinence, constipation, excessive secretions), pain, fatigue, and metabolic dysfunction [Mahoney et al 2021]. Despite advances in understanding the disease, the prognosis is ominous: median survival is three years, with most individuals dying of respiratory insufficiency [Masrori & Van Damme 2020].
DCTN1-related
progressive supranuclear palsy
(PSP) is characterized by supranuclear gaze palsy, postural instability, and increased falls within a year of symptom onset. However, the clinical presentation of PSP is heterogeneous, and it may initially mimic Parkinson disease, frontotemporal dementia, or corticobasal syndrome; rarely, pure akinesia with freezing of gait may be the only manifestation. In such instances, the classic features of PSP appear later in the disease course [Coughlin & Litvan 2020]. Most individuals with DCTN1-related PSP presented with dominant parkinsonian and FTD-like symptoms [Caroppo et al 2014, Gustavsson et al 2016, Konno et al 2017, Barreto et al 2021].
Neuroimaging and Other Studies
Reported findings [Felicio et al 2014, Barreto et al 2015, Hwang et al 2016, Konno et al 2017, Mishima et al 2018, Convery et al 2019, Coughlin & Litvan 2020, Masrori & Van Damme 2020, Saka et al 2010, Tian et al 2020, Mishima et al 2021, Tsuboi et al 2021, Zhang et al 2021]:
Brain CT and MRI may reveal atrophy of the frontal and temporal lobes or the midbrain.
18F-fluorodeoxyglucose positron emission tomography (FDG-PET) and single-photon emission CT (SPECT) may demonstrate decreased glucose metabolism and blood perfusion in the frontal, temporal, parietal, and occipital lobes.
123I-Ioflupane SPECT (DaTscan) may show reduced tracer uptake in the striatum, reflecting presynaptic dopaminergic dysfunction.
18F-6-fluoro-L-dopa (FDOPA) and 11C-dihydrotetrabenazine (DTBZ) PET may detect a decrease in striatal tracer uptake, reflecting presynaptic dopaminergic dysfunction.
11C-raclopride (RAC) PET may find an abnormal striatal tracer uptake, reflecting disturbances of postsynaptic dopaminergic function.
3-amino-4-(2-dimethylaminomethylphenylsulfanyl)-benzonitrile (DASB) PET may demonstrate cortical and subcortical disruption of serotonergic neurotransmission.
Transcranial sonography may show hyperechogenicity in the substantia nigra comparable to that observed in Parkinson disease.
131I-metaiodobenzylguanidine (131I-MIBG) myocardial scintigraphy may demonstrate reduced cardiac uptake, reflecting autonomic dysfunction.
Electroneurography may reveal length-dependent predominantly motor neuropathy.
Electromyography may show evidence of denervation.
Neuropathology
The neuropathology of DCTN1-related neurodegeneration is not well studied, and most autopsies were conducted on individuals with Perry syndrome.
Histology showed severe neuronal loss and gliosis in the substantia nigra, and to a lesser degree in locus ceruleus, striatum, hypothalamus, periaqueductal gray matter, ventrolateral medulla, dorsal raphe nucleus, and brain stem reticular formation. Lewy bodies and neurofibrillary tangles were not present in most individuals. Immunohistochemistry showed abnormal deposition of transactive response DNA-binding protein 43 (TDP-43) in the form of neuronal cytoplasmic inclusions, dystrophic neurites, glial cytoplasmic inclusions, and axonal spheroids. If present, TDP-43 pathology was morphologically similar in Perry syndrome, FTD, motor neuron disease, and other disorders. However, its distribution was distinct in individuals with Perry syndrome, who had most lesions located in the extrapyramidal system [Konno et al 2017, Mishima et al 2017, Mishima et al 2018].
In DCTN1-related dHMN7B, neuropathologic studies revealed decreased density of large myelinated nerve fibers and neurogenic changes in the muscles [Tian et al 2020, Zhang et al 2021]. TDP-43 aggregation was not observed [Mishima et al 2017]; however, it was detected in a cell model [Deshimaru et al 2021].