A longitudinal study of Taiwanese sialidosis type 1: an insight into the concept of cherry-red spot myoclonus syndrome

Unique clinical and electrophysiological features in the peripheral nerve system in patients with sialidosis - a case series study

BACKGROUND

To investigate the peripheral nervous system involvement in S sialidosis with typical features of myoclonus, seizure, and giant waves in somatosensory evoked potentials suggesting hyperexcitability in the central nervous system.

METHODS

The clinical presentation of patients with genetically confirmed sialidosis was recorded. Neurophysiological studies, including nerve conduction studies (NCSs), F-wave studies, and needle electromyography (EMG), were performed on these patients.

RESULTS

Six patients (M/F: 2:4) were recruited. In addition to the classical presentation, intermittent painful paresthesia was noted in four patients, and three of whom reported it as the earliest symptom. In the NCSs, one patient had reduced compound muscle action potential amplitudes in the right ulnar nerve, while another patient had prolonged distal motor latency in the bilateral tibial and peroneal nerves. Prolonged F-wave latency (83.3%), repeater F-waves (50%), and neurogenic polyphasic waves in EMG (in 2 out of 3 examined patients) were also noted. Interestingly, a very late response was noted in the F-wave study of all patients, probably indicating lesions involving the proximal peripheral nerve or spinal cord.

CONCLUSION

In addition to the central nervous system, the peripheral nervous system is also involved in sialidosis, with corresponding clinical symptoms. Further study on these phenomena is indicated.

Gene therapy corrects the neurological deficits of mice with sialidosis

Patients with sialidosis (mucolipidosis type I) type I typically present with myoclonus, seizures, ataxia, cherry-red spots, and blindness because of mutations in the neuraminidase 1 (NEU1) gene. Currently, there is no treatment for sialidosis. In this study, we developed an adeno-associated virus (AAV)-mediated gene therapy for a Neu1 knockout (Neu1-/-) mouse model of sialidosis. The vector, AAV9-P3-NP, included the human NEU1 promoter, NEU1 cDNA, IRES, and CTSA cDNA. Untreated Neu1-/- mice showed astrogliosis and microglial LAMP1 accumulation in the nervous system, including brain, spinal cord, and dorsal root ganglion, together with impaired motor function. Coexpression of NEU1 and protective protein/cathepsin A (PPCA) in neonatal Neu1-/- mice by intracerebroventricular injection, and less effective by facial vein injection, decreased astrogliosis and LAMP1 accumulation in the nervous system and improved rotarod performance of the treated mice. Facial vein injection also improved the grip strength and survival of Neu1-/- mice. Therefore, cerebrospinal fluid delivery of AAV9-P3-NP, which corrects the neurological deficits of mice with sialidosis, could be a suitable treatment for patients with sialidosis type I. After intracerebroventricular or facial vein injection of AAV vectors, NEU1 and PPCA are expressed together. PPCA-protected NEU1 is then sent to lysosomes, where β-Gal binds to this complex to form a multienzyme complex in order to execute its function.

Sialidosis type 1 without cherry-red spots: a case report and literature review

Background

Sialidosis is a rare disorder caused by mutations in the NEU1 gene located on chromosome 6p21.3, constituting a group of autosomal recessive diseases. Enzyme activity analysis, electron microscopy examination and genetic testing are reliable methods for diagnosis. Despite previous reports on the disease, its rarity means that its clinical manifestations and prognosis still warrant attention due to the limited amount of information available.

Methods

We report a case of a 40-year-old woman who was admitted to our hospital for worsening dysarthria of 16 years duration and facial and limb twitching that had been present for 2 years. Genetic testing was undertaken.

Results

Genetic testing confirmed type I sialidosis, the first reported instance of this disease in the Hainan Free Trade Port in China. The patient did not have the typical cherry-red spot in the fundus. Despite aggressive treatment, she died of status epilepticus 2 months later. This result indicates that the disease has a poor prognosis.

Discussion

Cherry-red spots in the fundus are characteristic features of type I sialidosis and it has been referred to as the cherry-red spot myoclonus syndrome. We hypothesise that environmental factors may also play a significant role. Overemphasis on the presence of cherry-red spots may mislead clinicians and delay diagnosis. Furthermore, patients presenting with isolated myoclonus should undergo visual evoked potential and somatosensory evoked potential tests, as well as genetic testing to confirm or rule out sialidosis.

NEU1—A Unique Therapeutic Target for Alzheimer’s Disease

Neuraminidase 1 (NEU1) is considered to be the most abundant and ubiquitous mammalian enzyme, with a broad tissue distribution. It plays a crucial role in a variety of cellular mechanisms. The deficiency of NEU1 has been implicated in various pathological manifestations of sialidosis and neurodegeneration. Thus, it is a novel therapeutic target for neurodegenerative changes in the Alzheimer’s brain. However, to manipulate NEU1 as a therapeutic target, it is imperative to understand that, although NEU1 is commonly known for its lysosomal catabolic function, it is also involved in other pathways. NEU1 is involved in immune response modulation, elastic fiber assembly modulation, insulin signaling, and cell proliferation. In recent years, our knowledge of NEU1 has continued to grow, yet, at the present moment, current data is still limited. In addition, the unique biochemical properties of NEU1 make it challenging to target it as an effective therapeutic option for sialidosis, which is a rare disease but has an enormous patient burden. However, the fact that NEU1 has been linked to the pathology of Alzheimer’s disease, which is rapidly growing worldwide, makes it more relevant to be studied and explored. In the present study, the authors have discussed various cellular mechanisms involving NEU1 and how they are relevant to sialidosis and Alzheimer’s disease.

Neurophysiolgical implications in sialidosis type 1: a case report

Sialidosis is a rare autosomal recessive hereditary disease caused by NEU1 gene mutations. A 25-year-old woman developed generalized tonic-clonic seizures since teenage, followed by progressive visional decline and limb myoclonus. Her sister had similar presentations. Both patients were products of a consanguineous marriage. Electroencephalography (EEG) revealed extensive paroxysmal spiky beta brush. Somatosensory evoked potentials (SEP) after stimulation of median nerves demonstrated giant SEP and C-reflex support the cortical origin of myoclonus. Genetic tests confirmed that both sisters carried the known pathogenic homozygous mutation of c.544A > G in exon 3 of the NEU1 gene. The diagnosis of sialidosis type 1 was then made. This suggests that neurophysiological abnormalities, especially spiky beta brush on EEG, might facilitate the early diagnosis of sialidosis type 1.

Autosomal recessive adult onset ataxia

Autosomal recessive ataxias (ARCA) represent a complex group of diseases ranging from primary ataxias to rare and complex metabolic disorders in which ataxia is a part of the clinical picture. Small number of ARCA manifest exclusively in adulthood, while majority of typical childhood onset ARCA may also start later with atypical clinical presentation. We have systematically searched the literature for ARCA with adult onset, both in the group of primary ataxias including those that are less frequently described in isolated or in a small number of families, and also in the group of complex and metabolic diseases in which ataxia is only part of the clinical picture. We propose an algorithm that could be used when encountering a patient with adult onset sporadic or recessive ataxia in whom the acquired causes are excluded. ARCA are frequently neglected in the differential diagnosis of adult-onset ataxias. Rising awareness of their clinical significance is important, not only because some of these disorders may be potentially treatable, but also for prognostic implications and inclusion of patients to future clinical trials with disease modifying agents.

Compound heterozygous mutations in the neuraminidase 1 gene in type 1 sialidosis: A case report and review of literature

BACKGROUND

Type 1 sialidosis, also known as cherry-red spot-myoclonus syndrome, is a rare autosomal recessive lysosomal storage disorder presenting in the second decade of life. The most common symptoms are myoclonus, ataxia and seizure. It is rarely encountered in the Chinese mainland.

CASE SUMMARY

A 22-year-old male presented with complaints of progressive myoclonus, ataxia and slurred speech, without visual symptoms; the presenting symptoms began at the age of 15-year-old. Whole exome sequencing revealed two pathogenic heterozygous missense variants [c.239C>T (p.P80L) and c.544A>G (p.S182G) in the neuraminidase 1 (NEU1) gene], both of which have been identified previously in Asian patients with type 1 sialidosis. All three patients identified in Mainland China come from three unrelated families, but all three show the NEU1 mutations p.S182G and p.P80L pathogenic variants. Increasing sialidase activity through chaperones is a promising therapeutic target in sialidosis.

CONCLUSION

Through retrospective analysis and summarizing the clinical and genetic characteristics of type 1 sialidosis, we hope to raise awareness of lysosomal storage disorders among clinicians and minimize the delay in diagnosis.

Myoclonus-Ataxia Syndromes: A Diagnostic Approach

Background

A myriad of disorders combine myoclonus and ataxia. Most causes are genetic and an increasing number of genes are being associated with myoclonus-ataxia syndromes (MAS), due to recent advances in genetic techniques. A proper etiologic diagnosis of MAS is clinically relevant, given the consequences for genetic counseling, treatment, and prognosis.

Objectives

To review the causes of MAS and to propose a diagnostic algorithm.

Methods

A comprehensive and structured literature search following PRISMA criteria was conducted to identify those disorders that may combine myoclonus with ataxia.

Results

A total of 135 causes of combined myoclonus and ataxia were identified, of which 30 were charted as the main causes of MAS. These include four acquired entities: opsoclonus-myoclonus-ataxia syndrome, celiac disease, multiple system atrophy, and sporadic prion diseases. The distinction between progressive myoclonus epilepsy and progressive myoclonus ataxia poses one of the main diagnostic dilemmas.

Conclusions

Diagnostic algorithms for pediatric and adult patients, based on clinical manifestations including epilepsy, are proposed to guide the differential diagnosis and corresponding work-up of the most important and frequent causes of MAS. A list of genes associated with MAS to guide genetic testing strategies is provided. Priority should be given to diagnose or exclude acquired or treatable disorders.

Sialidosis Type I without a Cherry Red Spot- Is There a Genetic Basis?

Sialidosis is an inborn error of metabolism due to a defect in the NEU1 gene and manifests as two phenotypes: mild type I and severe type II. The cherry red spot (CRS) is a characteristic feature in both types of sialidosis; reports of sialidosis without a CRS are rare. We report two cases of genetically confirmed sialidosis type I with a typical presentation of progressive cortical myoclonus and ataxia but without the CRS. A previously reported homozygous pathogenic variant p.Arg294Cys was detected in the first case, and a novel homozygous pathogenic variant p.Arg305Pro was detected in the second case. Additionally, we reviewed the literature describing cases with similar mutations to find a genetic basis for the absence of a CRS. Milder mutation of both alleles detected in both patients may be the reason for the absence of a CRS.

Clinical and genetic characteristics of type I sialidosis patients in mainland China

Objective

Type I sialidosis (ST‐1) is a rare autosomal recessive inherited disorder. To date, there has been no study on ST‐1 patients in mainland China.

Methods

We reported in detail the cases of five Chinese ST‐1 patients from two centers, and summarized all worldwide cases. Then, we compared the differences between Chinese and foreign patients.

Results

A total of 77 genetically confirmed ST‐1 patients were identified: 12 from mainland China, 23 from Taiwan, 10 from other Asian regions, and 32 from European and American regions. The mean age of onset was 16.0 ± 6.7 years; the most common symptoms were myoclonus seizures (96.0%), followed by ataxia (94.3%), and blurred vision (67.2%). Compared to other groups, the onset age of patients from mainland China was much younger (10.8 ± 2.7 years). The incidence of visual impairment was lower in patients from other Asian regions than in patients from mainland China and Taiwan (28.6% vs. 81.8%–100%). Cherry‐red spots were less frequent in the Taiwanese patients than in patients from other regions (27.3% vs. 55.2%–90.0%). Furthermore, 48 different mutation types were identified. Chinese mainland and Taiwanese patients were more likely to carry the c.544A > G mutation (75% and 100%, respectively) than the patients from other regions (only 0%–10.0%). Approximately 50% of Chinese mainland patients carried the c.239C > T mutation, a much higher proportion than that found in the other populations. In addition, although the brain MRI of most patients was normal, ¹⁸F‐FDG‐PET analysis could reveal cerebellar and occipital lobe hypometabolism.

Interpretation

ST‐1 patients in different regions are likely to have different mutation types; environmental factors may influence clinical manifestations. Larger studies enrolling more patients are required.

Genetic and clinical characterization of mainland Chinese patients with sialidosis type 1

Background

Sialidosis type 1 is a rare inherited disorder with a high disability. No genetically confirmed mainland Chinese patient with sialidosis type 1 has been reported. This study evaluated the phenotypes and genotypes of mainland Chinese patients with sialidosis type 1.

Methods

It was a retrospective case series study. Four unrelated patients were enrolled. Comprehensive clinical evaluations and molecular genetic analysis of the NEU1 gene were performed.

Results

Three out of four patients presented progressive myoclonus epilepsy. The best‐corrected visual acuity ranged from 20/2000 to 20/25. Punctate cataracts were found in all of the patients. Distinct macular cherry red spots were observed in three patients by fundoscopy, and a relatively normal fundus was revealed in one patient. Optical coherence tomography (OCT) showed increased reflectivity of the nerve fiber and ganglion cell layers, and fundus autofluorescence (FAF) revealed hyperautofluorescent areas surrounding the fovea in all of the patients. Only superficial retinal vessels can be observed using OCT angiography; the deeper capillary plexus could not be observed. Visual evoked potential revealed varying degrees of decreased amplitude and/or prolonged latency of P100 or P2 waves. The most frequent sequence variant identified was c.544A>G (p.S182G) (NM_000434.3).

Conclusions

Our study first described the ophthalmic and neurologic characteristics of a small cohort of unrelated mainland Chinese patients with sialidosis type 1. We found that c.544A>G (p. S182G) might be a hotspot variant in Chinese patients. The accumulation of metabolic products in the nerve fiber and ganglion cell layers is a characteristic ocular finding that could be sensitively detected by OCT and FAF imaging.

Heterozygous structural variation mimicking homozygous missense mutations in NEU1 associated with presenting clinical signs in eyes alone

INTRODUCTION

Biallelic mutations in neuraminidase 1 (NEU1) are associated with cherry-red spots. Whole genome sequencing contributes to eliminating pseudo-homozygous mutations when large-scale deletion of one allele in NEU1 and other genes occurs.

PATIENTS AND METHODS

Bilateral cherry-red spots in the macula were the only detectable sign in an 11-year-old girl with reduced visual acuity over the last two years. Targeted exome sequencing of genes for inherited eye diseases identified a homozygous c.544A>G (p.Ser182Gly) variation in the NEU1 gene. This variant was also present in her mother in the heterozygous state but not in her father. Whole genome sequencing identified a heterozygous 27.5 kb deletion involving the whole coding exons of NEU1 in her father. Sanger sequencing disclosed the breakpoint of the deletion. This heterozygous deletion was also detected in the patient, so the c.544A>G mutation should be heterozygous in the patient.

CONCLUSION

The results of this case remind us of the limitations of routine exome sequencing and the need to perform segregation studies and deletion/duplication analysis or WGS if parental studies do not support exome findings. In addition, patients with sialidosis may present with ocular manifestations without systemic signs early in the disease course.

Type I sialidosis, a normosomatic lysosomal disease, in the differential diagnosis of late-onset ataxia and myoclonus: An overview

Lysosomal storage diseases (LSDs) are rare to extremely rare monogenic disorders. Their incidence, however, has probably been underestimated owing to their complex clinical manifestations. Sialidosis is a prototypical LSD inherited as an autosomal recessive trait and caused by mutations in the NEU1 gene that result in a deficiency of alpha-N-acetyl neuraminidase 1 (NEU1). Two basic forms of this disease, type I and type II, are known. The dysmorphic type II form features LSD symptoms including congenital hydrops, dysmorphogenetic traits, hepato-splenomegaly and severe intellectual disability. The diagnosis is more challenging in the normosomatic type I forms, whose clinical findings at onset include ocular defects, ataxia and generalized myoclonus. Here we report the clinical, biochemical and molecular analysis of five patients with sialidosis type I. Two patients presented novel NEU1 mutations. One of these patients was compound heterozygous for two novel NEU1 missense mutations: c.530A>T (p.Asp177Val) and c.1010A>G (p.His337Arg), whereas a second patient was compound heterozygous for a known mutation and a novel c.839G>A (p.Arg280Gln) mutation. We discuss the impact of these new mutations on the structural properties of NEU1. We also review available clinical reports of patients with sialidosis type I, with the aim of identifying the most frequent initial clinical manifestations and achieving more focused diagnoses.

Type 1 Sialidosis Patient With a Novel Deletion Mutation in the NEU1 Gene: Case Report and Literature Review

Recent advances in next-generation sequencing technologies have uncovered the genetic backgrounds of various diseases. Type 1 sialidosis (OMIM#256550) is a rare autosomal recessive lysosomal storage disease caused by a mutation in the NEU1 (OMIM * 608272) gene. In this study, we aimed to review the previous reports of type 1 sialidosis and compare those with the first case of type 1 sialidosis in Korea. A 36-year-old woman presented with progressive ataxia, myoclonus, and seizure since the age of 12. Whole-exome sequencing revealed a pathogenic missense variant c.928G > A (p.D310N) and novel c.15_16del (p.P6Qfs*21) of the NEU1 gene as final causal candidate as compound heterozygotes. We reviewed the literature and selected the clinical reports of genetically confirmed type 1 sialidosis patients. A total of 45 patients in 17 reports were identified. Cherry-red spot, myoclonus, ataxia, and seizure were reported in 51.2%, 100.0%, 87.8%, and 73.7% of patients, respectively. Abnormalities of cognitive function, EEG, and brain MRI and visual symptoms were reported in 22.2%, 40.7%, 66.7%, and 70.2% of patients, respectively. Overall, our patient showed similar clinical features to previous type 1 sialidosis patients, but she did not complain of visual symptoms despite having cherry-red spots. We summarize the clinical features of type 1 sialidosis and report the first case of type 1 sialidosis with novel deletion variant in the NEU1 gene in the Korean population. Our study suggests the importance of ophthalmologic examinations in patients with myoclonus, ataxia, and seizure who do not complain of visual symptoms.

The Classification of Autosomal Recessive Cerebellar Ataxias: a Consensus Statement from the Society for Research on the Cerebellum and Ataxias Task Force

There is currently no accepted classification of autosomal recessive cerebellar ataxias, a group of disorders characterized by important genetic heterogeneity and complex phenotypes. The objective of this task force was to build a consensus on the classification of autosomal recessive ataxias in order to develop a general approach to a patient presenting with ataxia, organize disorders according to clinical presentation, and define this field of research by identifying common pathogenic molecular mechanisms in these disorders. The work of this task force was based on a previously published systematic scoping review of the literature that identified autosomal recessive disorders characterized primarily by cerebellar motor dysfunction and cerebellar degeneration. The task force regrouped 12 international ataxia experts who decided on general orientation and specific issues. We identified 59 disorders that are classified as primary autosomal recessive cerebellar ataxias. For each of these disorders, we present geographical and ethnical specificities along with distinctive clinical and imagery features. These primary recessive ataxias were organized in a clinical and a pathophysiological classification, and we present a general clinical approach to the patient presenting with ataxia. We also identified a list of 48 complex multisystem disorders that are associated with ataxia and should be included in the differential diagnosis of autosomal recessive ataxias. This classification is the result of a consensus among a panel of international experts, and it promotes a unified understanding of autosomal recessive cerebellar disorders for clinicians and researchers.

Clinical and electrophysiological characteristics of a type 1 sialidosis patient with a novel deletion mutation in NEU1 gene

BACKGROUND/PURPOSE

Type 1 sialidosis is a rare autosomal recessive lysosomal storage disease caused by Neuraminidase 1 (NEU1) gene mutations. We report a type 1 sialidosis patient with a novel deletion mutation in NEU1 and compared the phenotypes within different ethnicities.

METHODS

Targeted next generation sequencing and segregation analysis were performed to identify the causative gene mutation of the index patient. The clinical and electrophysiological characteristics of the patient were compared to those reported in previous studies of type 1 sialidosis from 1996 to 2019.

RESULTS

A 16-year-old boy presented with progressive onset of seizure, myoclonus, and ataxia since 5 years of age. Targeted next generation sequencing revealed the pathogenic missense variant c.544A>G (p.Ser182Gly) and the novel c.314_352del (p.A106_G118del) deletion in NEU1 in a compound heterozygote state. The leukocyte neuraminidase activity was significantly decreased (0.0323 nmol/mg protein/hour, normal reference: 0.326 ± 0.095 nmol/mg protein/hour). A total of 46 patients were identified in 18 reports from the literature. The most common symptoms were myoclonus (100%), followed by ataxia (88.3%) and seizure (72.5%). Notably, impaired cognition (50.0% vs. 21.7%, P = 0.04) and cherry-red spots (61.1% vs. 40.7%, P = 0.02) were less frequently reported in Asian patients than in Caucasian patients. Abnormal somatosensory evoked potentials with giant cortical waves and prolonged visual evoked potential latency were found consistently in Asian and Caucasian patients, and could be a surrogate marker of early diagnosis.

CONCLUSION

Our findings suggest a distinct phenotype of infrequent cherry-red spots and abnormal evoked potentials in Asian patients with type 1 sialidosis.

Seizure remission and improvement of neurological function in sialidosis with perampanel therapy

A 15-year-old boy experienced myoclonic seizures for 3 years. He initially had occasional myoclonus, gradually progressive ataxia, tremors, and psychomotor and speech regression developed. Eventually, he exhibited nearly continuous myoclonus. He received treatment of sodium valproate, levetiracetam, clobazam, and phenobarbital, without efficacy. A ketogenic diet also proved ineffective. Adjunctive therapy with 4 mg/day of perampanel was started and was gradually titrated to 10 mg/day. The remission of myoclonic seizures was achieved within one month. The patient's neurological and cognitive functions improved to a certain degree during the following 20 months. Sialidosis was confirmed by the mutations of NEU1 gene.

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A case of sialidosis I with compound mutations of c.544A > G and c.619C > T in NEU1 gene presented with drug-resistant seizures.

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Seizures associated with sialidosis eventually resolved on adjunctive perampanel therapy titrated to 10 mg/day.

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Our patient with sialidosis was drug-resistant to anti-seizure medication before responding to perampanel.

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Perampanel might be a potentially effective treatment for sialidosis in patients with Progressive Myoclonus Epilepsy.

Cortical damage in the posterior visual pathway in patients with sialidosis type 1

In order to identify the cortical changes in patients with Sialidosis type 1, diffusion tensor imaging and resting state fMRI were acquired from 11 patients and 11 sex/age matched normal controls after clinical evaluations. The neuroimages from each participant were normalized and parcellated according to the Automatic Anatomical Labeling. Both the mean diffusivity and the corresponding functional connectivity were calculated from each cortical region. The white matter tract integrity was examined. The difference between patients and controls was examined using Student's t-test and between patients with either homozygous or heterozygous mutations by Mann-Whitney U test, both at a threshold of 0.05. Increased mean diffusivity throughout the brain can be noticed in the patients, together with a compromised white matter tracts integrity. The most severely affected cortical regions are in the occipital lobe. Decreased functional connectivity was from the temporal and occipital lobes to the hippocampus and parahippocampus. In contrast, connectivity from thalamus was enhanced. Diffused cortical atrophy with posterior focal lesions was noticed. We concluded that MRI observed functional changes in the posterior cortical pathways in the patients with Sialidosis. The observation might be related to the cortical blindness due to an altered neural network and a compromised visual pathway in the patients.

Optical coherence tomography features in a case of Type I sialidosis

A 15-year-old boy presented with progressive myoclonic epilepsy and unbalance gaits for 4 years. Slit lamp examination showed a punctate cataract and funduscopic examination revealed bilateral macular cherry-red spots. Macular scan of spectral domain optical coherence tomography (SD-OCT) showed hyperreflectivity of the inner retinal layer and apparent hyperreflectivity of the photoreceptor layers in the foveal region. The clinical presentations were consistent with a Type I sialidosis which led to genetic analysis and revealed NEU1 mutation in this patient. He was under regular follow-up by ophthalmologist and neurologist. Sialidosis is a rare lysosomal storage disease resulting from a deficiency of alpha-N-acetyl neuraminidase caused by a mutation in the NEU1 gene. This results in abnormal intracellular accumulation of sialyloligosaccharides in brain neurons and ganglion cells of the retina. SD-OCT is a useful tool in detecting macular cherry-red spot and has a role in evaluating the extent of ganglion cell damage. It can aid in the differential diagnosis and long-term follow-up of the neurological metabolic disorders.

Clinical aspects of neuropathic lysosomal storage disorders

The purpose of this review is to describe neurological phenotypes associated with lysosomal storage diseases (LSDs), focusing on features arising from primary neuronal involvement. Clinical presentation, progression and genetic data, are discussed in detail in Part 2, the electronic material. Main features are summarized in Part 1. Insights gained from several observational studies are discussed. Prospective studies of the natural history of most neuronopathic LSDs have been hampered by the rarity of these conditions and the short survival of affected patients. Increasingly, longitudinal observations relating to neurological manifestations are being reported. Better clinical studies are necessary, including repeated measurements of disease progression to facilitate the development of sensitive scoring systems and appropriate counseling of affected individuals and their families. Ideally, clinical studies should involve a large cohort. As treatment becomes available, knowledge of disease expression and factors that influence the phenotype may enable critical assessment of therapeutic outcomes. It is hoped that increased familiarity with the clinical expression of individual LSDs will allow early diagnosis, so families at risk are given options to consider during future pregnancies. Early diagnosis also permits the introduction of timely intervention, to favoring improved outcome in cases that are potentially treatable.