Adult polyglucosan body disease masquerading as "ALS with dementia of the Alzheimer type": an exceptional phenotype in a rare pathology

Neuro-Ophthalmic Manifestations of Adult Polyglucosan Body Disease

BACKGROUND

Adult polyglucosan body disease (APBD) is caused by a deficiency in glycogen branching enzyme that leads to polyglucosan accumulation in multiple organs. It has a progressive clinical course with prominent neurologic manifestations. We aim to describe the neuro-ophthalmic manifestations of APBD.

METHODS

This is a case series of 3 individuals with genetically proven APBD. Written informed consent was provided by the brothers. We also performed a literature review on the current state of knowledge on APBD through PubMed.

RESULTS

Brother 1 developed gait imbalance and length-dependent polyneuropathy in his 40s followed by progressive urinary symptoms in his 50s. He reported diplopia and blurry vision in his 60s. Neuro-ophthalmic assessment revealed bilateral optic neuropathy, convergence insufficiency, and a right fourth nerve palsy. Genetic testing showed a homozygous pathogenic variant in GBE1 c.986A>C p.Tyr329Ser. Brother 2 developed progressive urinary symptoms in his 40s that were followed by cognitive deficits, length-dependent polyneuropathy, and lower extremity weakness in his 50s and 60s. He reported blurred vision, and neuro-ophthalmic evaluation revealed bilateral optic neuropathy. Genetic testing revealed the same variant as Brother 1, GBE1 c.986A>C p.Tyr329Ser. Brother 3 developed progressive urinary urgency and lower extremity weakness in his 50s followed by a length-dependent polyneuropathy in his 60s. He reported diplopia and blurry vision in his 70s. Neuro-ophthalmic assessment revealed bilateral optic neuropathy and convergence insufficiency. Genetic testing revealed the same variant as Brothers 1 and 2, GBE1 c.986A>C p.Tyr329Ser.

CONCLUSIONS

There is an array of afferent and efferent neuro-ophthalmic manifestations in APBD. Neuro-ophthalmic evaluation is crucial in evaluating and treating patients with APBD, particularly in those with visual dysfunction.

Diagnosis and management of glycogen storage disease type IV, including adult polyglucosan body disease: A clinical practice resource

Glycogen storage disease type IV (GSD IV) is an ultra-rare autosomal recessive disorder caused by pathogenic variants in GBE1 which results in reduced or deficient glycogen branching enzyme activity. Consequently, glycogen synthesis is impaired and leads to accumulation of poorly branched glycogen known as polyglucosan. GSD IV is characterized by a remarkable degree of phenotypic heterogeneity with presentations in utero, during infancy, early childhood, adolescence, or middle to late adulthood. The clinical continuum encompasses hepatic, cardiac, muscular, and neurologic manifestations that range in severity. The adult-onset form of GSD IV, referred to as adult polyglucosan body disease (APBD), is a neurodegenerative disease characterized by neurogenic bladder, spastic paraparesis, and peripheral neuropathy. There are currently no consensus guidelines for the diagnosis and management of these patients, resulting in high rates of misdiagnosis, delayed diagnosis, and lack of standardized clinical care. To address this, a group of experts from the United States developed a set of recommendations for the diagnosis and management of all clinical phenotypes of GSD IV, including APBD, to support clinicians and caregivers who provide long-term care for individuals with GSD IV. The educational resource includes practical steps to confirm a GSD IV diagnosis and best practices for medical management, including (a) imaging of the liver, heart, skeletal muscle, brain, and spine, (b) functional and neuromusculoskeletal assessments, (c) laboratory investigations, (d) liver and heart transplantation, and (e) long-term follow-up care. Remaining knowledge gaps are detailed to emphasize areas for improvement and future research.

Amyotrophic lateral sclerosis mimics

Amyotrophic lateral sclerosis (ALS) is the most common adult-onset motor neuron disorder characterized by progressive degeneration of cortical, bulbar, and spinal motor neurons. When a patient presents with a progressive upper and/or lower motor syndrome, clinicians must pay particular attention to any atypical features in the history and/or clinical examination suggesting an alternate diagnosis, as up to 10% percent of patients initially diagnosed with ALS have a mimic of ALS. ALS is a clinical diagnosis and requires the exclusion of other disorders that may have similar presentations but a more favorable prognosis or an effective therapy. Because there is currently no specific diagnostic biomarker that is sensitive or specific for ALS, understanding the spectrum of clinical presentations of ALS and its mimics is paramount. While true mimics of ALS are rare, the clinician must correctly identify these disorders to avoid the misdiagnosis of ALS and to initiate effective treatment where available.

Characterization of cognitive impairment in adult polyglucosan body disease

Adult polyglucosan body disease (APBD) is a rare but probably underdiagnosed autosomal recessive neurodegenerative disorder due to pathogenic variants in GBE1. The phenotype is characterized by neurogenic bladder dysfunction, spastic paraplegia, and axonal neuropathy. Additionally, cognitive symptoms and dementia have been reported in APBD but have not been studied systematically. Using exome sequencing, we identified two previously unreported bi-allelic missense GBE1 variants in a patient with severe memory impairment along with the typical non-cognitive symptoms. We were able to confirm a reduction of GBE1 activity in blood lymphocytes. To characterize the neuropsychological profile of patients suffering from APBD, we conducted a systematic review of cognitive impairment in this rare disease. Analysis of 24 cases and case series (in total 58 patients) showed that executive deficits and memory impairment are the most common cognitive symptoms in APBD.

GBE1-related disorders: Adult polyglucosan body disease and its neuromuscular phenotypes

Adult polyglucosan body disease (APBD) represents a complex autosomal recessive inherited neurometabolic disorder due to homozygous or compound heterozygous pathogenic variants in GBE1 gene, resulting in deficiency of glycogen-branching enzyme and secondary storage of glycogen in the form of polyglucosan bodies, involving the skeletal muscle, diaphragm, peripheral nerve (including autonomic fibers), brain white matter, spinal cord, nerve roots, cerebellum, brainstem and to a lesser extent heart, lung, kidney, and liver cells. The diversity of new clinical presentations regarding neuromuscular involvement is astonishing and transformed APBD in a key differential diagnosis of completely different clinical conditions, including axonal and demyelinating sensorimotor polyneuropathy, progressive spastic paraparesis, motor neuronopathy presentations, autonomic disturbances, leukodystrophies or even pure myopathic involvement with limb-girdle pattern of weakness. This review article aims to summarize the main clinical, biochemical, genetic, and diagnostic aspects regarding APBD with special focus on neuromuscular presentations.

First Report on Fetal Cerebral Polyglucosan Bodies in Mucopolysaccharidosis Type VII

We report on the detection of discordant inclusions in the brain of a 25-week female fetus with a very rare lysosomal storage disease, namely, Sly disease (mucopolysaccharidosis (MPS) type VII), presenting with nonimmune hydrops fetalis. Besides vacuolated neurons, we found abundant deposition of polyglucosan bodies (PGBs) in the developing brain of this fetus in whom MPS-VII was corroborated by lysosomal beta-glucuronidase-deficiency detected in fetal blood and fetal skin-fibroblasts and by the presence of a heterozygous pathogenic variant in the GUSB gene in the mother. Fetal/neonatal metabolic disorders with PGB-deposition are extremely rare (particularly in relation to CNS involvement) and include almost exclusively subtypes of glycogenosis (types IV and VII). The accumulation of PGBs (particularly in the fetal brain) has so far not been depicted in Sly disease. This is the first report on such “aberrant” association. Besides, the detection of these CNS inclusions at such an early developmental stage is remarkably unique.

Immununochemical Markers of the Amyloid Cascade in the Hippocampus in Motor Neuron Diseases

BACKGROUND

Several findings suggest that the amyloid precursor protein (APP) and the amyloid cascade may play a role in motor neuron disease (MND).

OBJECTIVE

Considering that dementia is one of the most frequent non-motor symptoms in amyotrophic lateral sclerosis (ALS) and that hippocampus is one of the brain areas with greater presence of amyloid-related changes in neurodegenerative diseases, our aim was to analyze the molecular markers of the amyloid cascade of APP in pathology studies of the hippocampus of autopsied patients with ALS and ALS-frontotemporal dementia (FTD).

METHODS

We included nine patients with MND and four controls. Immunohistochemical studies and confocal microscopy were used to analyze the expression of APP, TDP-43, pho-TDP-43, Aβ, APP intracellular cytoplasmatic domain (AICD) peptide, Fe65 protein, and pho-TAU in the hippocampus of seven patients with ALS, two patients with ALS-FTD, and four controls. These findings were correlated with clinical data.

RESULTS

Patients displayed increased expression of APP and Aβ peptide. The latter was correlated with cytoplasmic pho-TDP-43 expression. We also found decreased Fe65 expression. A parallel increase in AICD expression was not found. Patients showed increased expression of pho-TAU in the hippocampus. Findings were similar in patients with ALS and those with ALS-FTD, though more marked in the latter group.

CONCLUSION

Post-mortem analyses showed that the amyloid cascade is activated in the hippocampus of patients with MND and correlated with cytoplasmic pho-TDP-43 expression. The number of intracellular or extracellular aggregates of Aβ peptides was not significant.

Tongue atrophy and fasciculations in transthyretin familial amyloid neuropathy: An ALS mimicker

Objective:

Macroglossia is a well-known feature of amyloidosis; however, tongue atrophy and fasciculations are rarely seen and can lead to the misdiagnosis of amyotrophic lateral sclerosis (ALS).

Methods:

We identified 2 unrelated patients with atypical features of tongue atrophy and fasciculations in the setting of a severe neuropathy.

Results:

Both patients were confirmed to have transthyretin-related familial amyloid polyneuropathy (TTR-FAP) by genetic testing.

Conclusions:

TTR-FAP should be considered as a possible mimicker of ALS when tongue atrophy and fasciculations are seen in the setting of a severely progressive polyneuropathy. Other atypical mimickers of ALS include polyglucosan body disease, hexosaminidase A deficiency, multisystem proteinopathy, and Allgrove syndrome.

A(a)LS: Ammonia-induced amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a dreadful, devastating and incurable motor neuron disease. Aetiologically, it is a multigenic, multifactorial and multiorgan disease. Despite intense research, ALS pathology remains unexplained. Following extensive literature review, this paper posits a new integrative explanation. This framework proposes that ammonia neurotoxicity is a main player in ALS pathogenesis. According to this explanation, a combination of impaired ammonia removal- mainly because of impaired hepatic urea cycle dysfunction-and increased ammoniagenesis- mainly because of impaired glycolytic metabolism in fast twitch skeletal muscle-causes chronic hyperammonia in ALS. In the absence of neuroprotective calcium binding proteins (calbindin, calreticulin and parvalbumin), elevated ammonia-a neurotoxin-damages motor neurons. Ammonia-induced motor neuron damage occurs through multiple mechanisms such as macroautophagy-endolysosomal impairment, endoplasmic reticulum (ER) stress, CDK5 activation, oxidative/nitrosative stress, neuronal hyperexcitability and neuroinflammation. Furthermore, the regional pattern of calcium binding proteins' loss, owing to either ER stress and/or impaired oxidative metabolism, determines clinical variability of ALS. Most importantly, this new framework can be generalised to explain other neurodegenerative disorders such as Huntington's disease and Parkinsonism.

Adult polyglucosan body disease: Natural History and Key Magnetic Resonance Imaging Findings

OBJECTIVE

Adult polyglucosan body disease (APBD) is an autosomal recessive leukodystrophy characterized by neurogenic bladder, progressive spastic gait, and peripheral neuropathy. Polyglucosan bodies accumulate in the central and peripheral nervous systems and are often associated with glycogen branching enzyme (GBE) deficiency. To improve clinical diagnosis and enable future evaluation of therapeutic strategies, we conducted a multinational study of the natural history and imaging features of APBD.

METHODS

We gathered clinical, biochemical, and molecular findings in 50 APBD patients with GBE deficiency from Israel, the United States, France, and the Netherlands. Brain and spine magnetic resonance images were reviewed in 44 patients.

RESULTS

The most common clinical findings were neurogenic bladder (100%), spastic paraplegia with vibration loss (90%), and axonal neuropathy (90%). The median age was 51 years for the onset of neurogenic bladder symptoms, 63 years for wheelchair dependence, and 70 years for death. As the disease progressed, mild cognitive decline may have affected up to half of the patients. Neuroimaging showed hyperintense white matter abnormalities on T2 and fluid attenuated inversion recovery sequences predominantly in the periventricular regions, the posterior limb of the internal capsule, the external capsule, and the pyramidal tracts and medial lemniscus of the pons and medulla. Atrophy of the medulla and spine was universal. p.Y329S was the most common GBE1 mutation, present as a single heterozygous (28%) or homozygous (48%) mutation.

INTERPRETATION

APBD with GBE deficiency, with occasional exceptions, is a clinically homogenous disorder that should be suspected in patients with adult onset leukodystrophy or spastic paraplegia with early onset of urinary symptoms and spinal atrophy.